A 20-year overview of fertility preservation in boys: new insights gained through a comprehensive international survey

STUDY QUESTION

Twenty years after the inception of the first fertility preservation programme for pre-pubertal boys, what are the current international practices with regard to cryopreservation of immature testicular tissue?

SUMMARY ANSWER

Worldwide, testicular tissue has been cryopreserved from over 3000 boys under the age of 18 years for a variety of malignant and non-malignant indications; there is variability in practices related to eligibility, clinical assessment, storage, and funding.

WHAT IS KNOWN ALREADY

For male patients receiving gonadotoxic treatment prior to puberty, testicular tissue cryopreservation may provide a method of fertility preservation. While this technique remains experimental, an increasing number of centres worldwide are cryopreserving immature testicular tissue and are approaching clinical application of methods to use this stored tissue to restore fertility. As such, standards for quality assurance and clinical care in preserving immature testicular tissue should be established.

STUDY DESIGN SIZE DURATION

A detailed survey was sent to 17 centres within the recently established ORCHID-NET consortium, which offer testicular tissue cryopreservation to patients under the age of 18 years. The study encompassed 60 questions and remained open from 1 July to 1 November 2022.

PARTICIPANTS/MATERIALS SETTING METHODS

Of the 17 invited centres, 16 completed the survey, with representation from Europe, Australia, and the USA. Collectively, these centres have cryopreserved testicular tissue from patients under the age of 18 years. Data are presented using descriptive analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Since the establishment of the first formal fertility preservation programme for pre-pubertal males in 2002, these 16 centres have cryopreserved tissue from 3118 patients under the age of 18 years, with both malignant (60.4%) and non-malignant (39.6%) diagnoses. All centres perform unilateral biopsies, while 6/16 sometimes perform bilateral biopsies. When cryopreserving tissue, 9/16 centres preserve fragments sized ≤5 mm3 with the remainder preserving fragments sized 6-20 mm3. Dimethylsulphoxide is commonly used as a cryoprotectant, with medium supplements varying across centres. There are variations in funding source, storage duration, and follow-up practice. Research, with consent, is conducted on stored tissue in 13/16 centres.

LIMITATIONS REASONS FOR CAUTION

While this is a multi-national study, it will not encompass every centre worldwide that is cryopreserving testicular tissue from males under 18 years of age. As such, it is likely that the actual number of patients is even higher than we report. Whilst the study is likely to reflect global practice overall, it will not provide a complete picture of practices in every centre.

WIDER IMPLICATIONS OF THE FINDINGS

Given the research advances, it is reasonable to suggest that cryopreserved immature testicular tissue will in the future be used clinically to restore fertility. The growing number of patients undergoing this procedure necessitates collaboration between centres to better harmonize clinical and research protocols evaluating tissue function and clinical outcomes in these patients.

STUDY FUNDING/COMPETING INTERESTS

K.D. is supported by a CRUK grant (C157/A25193). R.T.M. is supported by an UK Research and Innovation (UKRI) Future Leaders Fellowship (MR/S017151/1). The MRC Centre for Reproductive Health at the University of Edinburgh is supported by MRC (MR/N022556/1). C.L.M. is funded by Kika86 and ZonMW TAS 116003002. A.M.M.v.P. is supported by ZonMW TAS 116003002. E.G. was supported by the Research Program of the Research Foundation-Flanders (G.0109.18N), Kom op tegen Kanker, the Strategic Research Program (VUB_SRP89), and the Scientific Fund Willy Gepts. J.-B.S. is supported by the Swedish Childhood Cancer Foundation (TJ2020-0026). The work of NORDFERTIL is supported by the Swedish Childhood Cancer Foundation (PR2019-0123; PR2022-0115), the Swedish Research Council (2018-03094; 2021-02107), and the Birgitta and Carl-Axel Rydbeck's Research Grant for Paediatric Research (2020-00348; 2021-00073; 2022-00317; 2023-00353). C.E is supported by the Health Department of the Basque Government (Grants 2019111068 and 2022111067) and Inocente Inocente Foundation (FII22/001). M.P.R. is funded by a Medical Research Council Centre for Reproductive Health Grant No: MR/N022556/1. A.F. and N.R. received support from a French national research grant PHRC No. 2008/071/HP obtained by the French Institute of Cancer and the French Healthcare Organization. K.E.O. is funded by the University of Pittsburgh Medical Center and the US National Institutes of Health HD100197. V.B-L is supported by the French National Institute of Cancer (Grant Seq21-026). Y.J. is supported by the Royal Children's Hospital Foundation and a Medical Research Future Fund MRFAR000308. E.G., N.N., S.S., C.L.M., A.M.M.v.P., C.E., R.T.M., K.D., M.P.R. are members of COST Action CA20119 (ANDRONET) supported by COST (European Cooperation in Science and Technology). The Danish Child Cancer Foundation is also thanked for financial support (C.Y.A.). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Germline specific genes increase DNA double-strand break repair and radioresistance in lung adenocarcinoma cells

In principle, germline cells possess the capability to transmit a nearly unaltered set of genetic material to infinite future generations, whereas somatic cells are limited by strict growth constraints necessary to assure an organism's physical structure and eventual mortality. As the potential to replicate indefinitely is a key feature of cancer, we hypothesized that the activation of a "germline program" in somatic cells can contribute to oncogenesis. Our group recently described over one thousand germline specific genes that can be ectopically expressed in cancer, yet how germline specific processes contribute to the malignant properties of cancer is poorly understood. We here show that the expression of germ cell/cancer (GC) genes correlates with malignancy in lung adenocarcinoma (LUAD). We found that LUAD cells expressing more GC genes can repair DNA double strand breaks more rapidly, show higher rates of proliferation and are more resistant to ionizing radiation, compared to LUAD cells that express fewer GC genes. In particular, we identified the HORMA domain protein regulator TRIP13 to be predominantly responsible for this malignant phenotype, and that TRIP13 inhibition or expression levels affect the response to ionizing radiation and subsequent DNA repair. Our results demonstrate that GC genes are viable targets in oncology, as they induce increased radiation resistance and increased propagation in cancer cells. Because their expression is normally restricted to germline cells, we anticipate that GC gene directed therapeutic options will effectively target cancer, with limited side effects besides (temporary) infertility.

Favorable culture conditions for spermatogonial propagation in human and non-human primate primary testicular cell cultures: a systematic review and meta-analysis

Introduction: Autologous transplantation of spermatogonial stem cells (SSCs) isolated from cryopreserved testicular biopsies obtained before oncological treatment could restore fertility in male childhood cancer survivors. There is a clear necessity for in vitro propagation of the limited SSCs from the testicular biopsy prior to transplantation due to limited numbers of spermatogonia in a cryopreserved testicular biopsy. Still, there is no consensus regarding their optimal culture method. Methods: We performed a systematic review and meta-analysis of studies reporting primary testicular cell cultures of human and non-human primate origin through use of Pubmed, EMBASE, and Web of Science core collection databases. Of 760 records, we included 42 articles for qualitative and quantitative analysis. To quantify in vitro spermatogonial propagation, spermatogonial colony doubling time (CDT) was calculated, which measures the increase in the number of spermatogonial colonies over time. A generalized linear mixed model analysis was used to assess the statistical effect of various culture conditions on CDT. Results: Our analysis indicates decreased CDTs, indicating faster spermatogonial propagation in cultures with a low culture temperature (32°C); with use of non-cellular matrices; use of StemPro-34 medium instead of DMEM; use of Knockout Serum Replacement; and when omitting additional growth factors in the culture medium. Discussion: The use of various methods and markers to detect the presence of spermatogonia within the reported cultures could result in detection bias, thereby potentially influencing comparability between studies. However, through use of CDT in the quantitative analysis this bias was reduced. Our results provide insight into critical culture conditions to further optimize human spermatogonial propagation in vitro, and effectively propagate and utilize these cells in a future fertility restoration therapy and restore hope of biological fatherhood for childhood cancer survivors.

EP300 facilitates human trophoblast stem cell differentiation

Early placenta development involves cytotrophoblast differentiation into extravillous trophoblast (EVT) and syncytiotrophoblast (STB). Defective trophoblast development and function may result in severe pregnancy complications, including fetal growth restriction and pre-eclampsia. The incidence of these complications is increased in pregnancies of fetuses affected by Rubinstein-Taybi syndrome, a developmental disorder predominantly caused by heterozygous mutations in CREB-binding protein (CREBBP) or E1A-binding protein p300 (EP300). Although the acetyltransferases CREBBP and EP300 are paralogs with many overlapping functions, the increased incidence of pregnancy complications is specific for EP300 mutations. We hypothesized that these complications have their origin in early placentation and that EP300 is involved in that process. Therefore, we investigated the role of EP300 and CREBBP in trophoblast differentiation, using human trophoblast stem cells (TSCs) and trophoblast organoids. We found that pharmacological CREBBP/EP300 inhibition blocks differentiation of TSCs into both EVT and STB lineages, and results in an expansion of TSC-like cells under differentiation-inducing conditions. Specific targeting by RNA interference or CRISPR/Cas9-mediated mutagenesis demonstrated that knockdown of EP300 but not CREBBP, inhibits trophoblast differentiation, consistent with the complications seen in Rubinstein-Taybi syndrome pregnancies. By transcriptome sequencing, we identified transforming growth factor alpha (TGFA, encoding TGF-α) as being strongly upregulated upon EP300 knockdown. Moreover, supplementing differentiation medium with TGF-α, which is a ligand for the epidermal growth factor receptor (EGFR), likewise affected trophoblast differentiation and resulted in increased TSC-like cell proliferation. These findings suggest that EP300 facilitates trophoblast differentiation by interfering with at least EGFR signaling, pointing towards a crucial role for EP300 in early human placentation.

Sperm DNA methylation is predominantly stable in mice offspring born after transplantation of long-term cultured spermatogonial stem cells

BACKGROUND

Spermatogonial stem cell transplantation (SSCT) is proposed as a fertility therapy for childhood cancer survivors. SSCT starts with cryopreserving a testicular biopsy prior to gonadotoxic treatments such as cancer treatments. When the childhood cancer survivor reaches adulthood and desires biological children, the biopsy is thawed and SSCs are propagated in vitro and subsequently auto-transplanted back into their testis. However, culturing stress during long-term propagation can result in epigenetic changes in the SSCs, such as DNA methylation alterations, and might be inherited by future generations born after SSCT. Therefore, SSCT requires a detailed preclinical epigenetic assessment of the derived offspring before this novel cell therapy is clinically implemented. With this aim, the DNA methylation status of sperm from SSCT-derived offspring, with in vitro propagated SSCs, was investigated in a multi-generational mouse model using reduced-representation bisulfite sequencing.

RESULTS

Although there were some methylation differences, they represent less than 0.5% of the total CpGs and methylated regions, in all generations. Unsupervised clustering of all samples showed no distinct grouping based on their pattern of methylation differences. After selecting the few single genes that are significantly altered in multiple generations of SSCT offspring compared to control, we validated the results with quantitative Bisulfite Sanger sequencing and RT-qPCRin various organs. Differential methylation was confirmed only for Tal2, being hypomethylated in sperm of SSCT offspring and presenting higher gene expression in ovaries of SSCT F1 offspring compared to control F1.

CONCLUSIONS

We found no major differences in DNA methylation between SSCT-derived offspring and control, both in F1 and F2 sperm. The reassuring outcomes from our study are a prerequisite for promising translation of SSCT to the human situation.

Childhood cancer and hematological disorders negatively affect spermatogonial quantity at diagnosis: a retrospective study of a male fertility preservation cohort

STUDY QUESTION

What is the impact of cancer or hematological disorders on germ cells in pediatric male patients?

SUMMARY ANSWER

Spermatogonial quantity is reduced in testes of prepubertal boys diagnosed with cancer or severe hematological disorder compared to healthy controls and this reduction is disease and age dependent: patients with central nervous system cancer (CNS tumors) and hematological disorders, as well as boys <7 years are the most affected.

WHAT IS KNOWN ALREADY

Fertility preservation in pediatric male patients is considered based on the gonadotoxicity of selected treatments. Although treatment effects on germ cells have been extensively investigated, limited data are available on the effect of the disease on the prepubertal male gonad. Of the few studies investigating the effects of cancer or hematologic disorders on testicular function and germ cell quantity in prepuberty, the results are inconsistent. However, recent studies suggested impairments before the initiation of known gonadotoxic therapy. Understanding which diseases and at what age affect the germ cell pool in pediatric patients before treatment is critical to optimize strategies and counseling for fertility preservation.

STUDY DESIGN, SIZE, DURATION

This multicenter retrospective cohort study included 101 boys aged <14 years with extra-cerebral cancer (solid tumors), CNS tumors, leukemia/lymphoma (blood cancer), or non-malignant hematological disorders, who were admitted for a fertility preservation programme between 2002 and 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In addition to clinical data, we analyzed measurements of testicular volume and performed histological staining on testicular biopsies obtained before treatment, at cryopreservation, to evaluate number of spermatogonia per tubular cross-section, tubular fertility index, and the most advanced germ cell type prior to chemo-/radiotherapy. The controls were data simulations with summary statistics from original studies reporting healthy prepubertal boys' testes characteristics.

MAIN RESULTS AND THE ROLE OF CHANCE

Prepubertal patients with childhood cancer or hematological disorders were more likely to have significantly reduced spermatogonial quantity compared to healthy controls (48.5% versus 31.0% prevalence, respectively). The prevalence of patients with reduced spermatogonial quantity was highest in the CNS tumor (56.7%) and the hematological disorder (55.6%) groups, including patients with hydroxyurea pre-treated sickle cell disease (58.3%) and patients not exposed to hydroxyurea (50%). Disease also adversely impacted spermatogonial distribution and differentiation. Irrespective of disease, we observed the highest spermatogonial quantity reduction in patients <7 years of age.

LIMITATIONS, REASONS FOR CAUTION

For ethical reasons, we could not collect spermatogonial quantity data in healthy prepubertal boys as controls and thus deployed statistical simulation on data from literature. Also, our results should be interpreted considering low patient numbers per (sub)group.

WIDER IMPLICATIONS OF THE FINDINGS

Cancers, especially CNS tumors, and severe hematological disorders can affect spermatogonial quantity in prepubertal boys before treatment. Consequently, these patients may have a higher risk of depleted spermatogonia following therapies, resulting in persistent infertility. Therefore, patient counseling prior to disease treatment and timing of fertility preservation should not only be based on treatment regimes, but also on diagnoses and age.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Marie Curie Initial Training Network (ITN) (EU-FP7-PEOPLE-2013-ITN) funded by European Commision grant no. 603568; ZonMW Translational Adult stem cell research (TAS) grant no. 116003002. No competing interests.

TRIAL REGISTRATION NUMBER

N/A.

How germline genes promote malignancy in cancer cells

Cancers often express hundreds of genes otherwise specific to germ cells, the germline/cancer (GC) genes. Here, we present and discuss the hypothesis that activation of a "germline program" promotes cancer cell malignancy. We do so by proposing four hallmark processes of the germline: meiosis, epigenetic plasticity, migration, and metabolic plasticity. Together, these hallmarks enable replicative immortality of germ cells as well as cancer cells. Especially meiotic genes are frequently expressed in cancer, implying that genes unique to meiosis may play a role in oncogenesis. Because GC genes are not expressed in healthy somatic tissues, they form an appealing source of specific treatment targets with limited side effects besides infertility. Although it is still unclear why germ cell specific genes are so abundantly expressed in cancer, from our hypothesis it follows that the germline's reproductive program is intrinsic to cancer development.

Transcriptional comparison of testicular adrenal rest tumors with fetal and adult tissues

BACKGROUND

Testicular adrenal rest tumors (TART) are a common complication of unknown cellular origin in patients with congenital adrenal hyperplasia (CAH). These benign tumors have both adrenal and testicular characteristics and are hypothesized to either derive from cells of adrenal origin from the fetal adrenogonadal primordium or by atypical differentiation of adult Leydig-progenitor cells.

OBJECTIVE

This study aims to unravel the identity and etiology of TART.

METHODS

Co-expression of adrenal-specific CYP11B1 and Leydig cell-specific HSD17B3 in TART was studied using immunohistochemistry. We studied the possibility of TART being derived from atypical differentiation of adult Leydig-progenitor cells by the quantification of adrenal-specific enzyme expression upon adrenocorticotrophic hormone (ACTH)-like stimulation of ex vivo cultured platelet-derived growth factor receptor alpha-positive cells. By comparing the transcriptome of TART (n = 16) with the transcriptome of fetal adrenal (n = 13), fetal testis (n = 5), adult adrenal (n = 11), and adult testis (n = 10) tissues, we explored the identity of TART.

RESULTS

We demonstrate co-expression of adrenal-specific CYP11B1 and testis-specific HSD17B3 in TART cells, indicating the existence of a distinct TART cell exhibiting both adrenal and testicular characteristics. Ex vivo cultured adult Leydig-progenitor cells did not express the ACTH-receptor MC2R but did express CYP11B1 upon stimulation. Unsupervised clustering of transcriptome data showed that TART was most similar to adult adrenal tissue, followed by adult testis tissue, and least similar to either fetal tissue.

CONCLUSION

Our data suggest that TART is induced - most likely via activation of a cAMP/protein kinase A-dependent receptor - from a progenitor cell into a unique mature adrenal-like cell type, sometimes exhibiting both adrenal and testicular features.

Spermatogonial Stem Cell-Based Therapies: Taking Preclinical Research to the Next Level

Fertility preservation via biobanking of testicular tissue retrieved from testicular biopsies is now generally recommended for boys who need to undergo gonadotoxic treatment prior to the onset of puberty, as a source of spermatogonial stem cells (SSCs). SSCs have the potential of forming spermatids and may be used for therapeutic fertility approaches later in life. Although in the past 30 years many milestones have been reached to work towards SSC-based fertility restoration therapies, including transplantation of SSCs, grafting of testicular tissue and various in vitro and ex vivo spermatogenesis approaches, unfortunately, all these fertility therapies are still in a preclinical phase and not yet available for patients who have become infertile because of their treatment during childhood. Therefore, it is now time to take the preclinical research towards SSC-based therapy to the next level to resolve major issues that impede clinical implementation. This review gives an outline of the state of the art of the effectiveness and safety of fertility preservation and SSC-based therapies and addresses the hurdles that need to be taken for optimal progression towards actual clinical implementation of safe and effective SSC-based fertility treatments in the near future.

In Vitro Meiosis of Male Germline Stem Cells

In vitro spermatogenesis has been achieved by culturing mouse embryonic stem cells (ESCs) together with a cell suspension of male juvenile gonad. However, for human fertility treatment or preservation, patient-specific ESCs or juvenile gonad is not available. We therefore aim to achieve in vitro spermatogenesis using male germline stem cells (GSCs) without the use of juvenile gonad. GSCs, when cultured on immortalized Sertoli cells, were able to enter meiosis, reach the meiotic metaphase stages, and sporadically form spermatid-like cells. However, the in vitro-formed pachytene-like spermatocytes did not display full chromosome synapsis and did not form meiotic crossovers. Despite this, the meiotic checkpoints that usually eliminate such cells to prevent genomic instabilities from being transmitted to the offspring were not activated, allowing the cells to proceed to the meiotic metaphase stages. In vitro-generated spermatid-like cells should thus be thoroughly investigated before being considered for clinical use.

Comparison of DNA methylation patterns of parentally imprinted genes in placenta derived from IVF conceptions in two different culture media

Study question

Is there a difference in DNA methylation status of imprinted genes in placentas derived from IVF conceptions where embryo culture was performed in human tubal fluid (HTF) versus G5 culture medium?

Summary answer

We found no statistically significant differences in the mean DNA methylation status of differentially methylated regions (DMRs) associated with parentally imprinted genes in placentas derived from IVF conceptions cultured in HTF versus G5 culture medium.

What is known already

Animal studies indicate that the embryo culture environment affects the DNA methylation status of the embryo. In humans, birthweight is known to be affected by the type of embryo culture medium used. The effect of embryo culture media on pregnancy, birth and child development may thus be mediated by differential methylation of parentally imprinted genes in the placenta.

Study design, size, duration

To identify differential DNA methylation of imprinted genes in human placenta derived from IVF conceptions exposed to HTF or G5 embryo culture medium, placenta samples (n = 43 for HTF, n = 54 for G5) were collected between 2010 and 2012 s as part of a multi-center randomized controlled trial in the Netherlands comparing these embryo culture media. Placenta samples from 69 naturally conceived (NC) live births were collected during 2008–2013 in the Netherlands as reference material.

Participants/materials, setting, methods

To identify differential DNA methylation of imprinted genes, we opted for an amplicon-based sequencing strategy on an Illumina MiSeq sequencing platform. DNA was isolated and 34 DMRs associated with well-defined parentally imprinted genes were amplified in a two-step PCR before sequencing using MiSeq technology. Sequencing data were analyzed in a multivariate fashion to eliminate possible confounding effects.

Main results and the role of chance

We found no statistically significant differences in the mean DNA methylation status of any of the imprinted DMRs in placentas derived from IVF conceptions cultured in HTF or G5 culture medium. We also did not observe any differences in the mean methylation status per amplicon nor in the variance in methylation per amplicon between the two culture medium

groups. A separate surrogate variable analysis also demonstrated that the IVF culture medium was not associated with the DNA methylation status of these DMRs. The mean methylation level and variance per CpG was equal between HTF and G5 placenta. Additional comparison of DNA methylation status of NC placenta samples revealed no statistically significant differences in mean amplicon and CpG methylation between G5, HTF and NC placenta; however, the number of placenta samples exhibiting outlier methylation levels was higher in IVF placenta compared to NC (P < 0.00001). Also, we were able to identify 37 CpG sites that uniquely displayed outlier methylation in G5 placentas and 32 CpG sites that uniquely displayed outlier methylation in HTF. In 8/37 (G5) and 4/32 (HTF) unique outliers CpGs, a medium-specific unique outlier could be directly correlated to outlier methylation of the entire amplicon.

Limitations, reasons for caution

Due to practical reasons, not all placentas were collected during the trial, and we collected the placentas from natural conceptions from a different cohort, potentially creating bias. We limited ourselves to the DNA methylation status of 34 imprinted DMRs, and we studied only the placenta and no other embryo-derived tissues.

Wider implications of the findings

It has often been postulated, but has yet to be rigorously tested, that imprinting mediates the effects of embryo culture conditions on pregnancy, birth and child development in humans. Since we did not detect any statistically significant effects of embryo culture conditions on methylation status of imprinted genes in the placenta, this suggests that other unexplored mechanisms may underlie these effects. The biological and clinical relevance of detected outliers with respect to methylation levels of CpGs and DMR require additional analysis in a larger sample size as well. Given the importance and the growing number of children born through IVF, research into these molecular mechanisms is urgently needed.

Study funding/competing interest(s)

This study was funded by the March of Dimes grant number #6-FY13-153. The authors have no conflicts of interest.

Trial registration number

Placental biopsies were obtained under Netherlands Trial Registry number 1979 and 1298.

Fertility preservation for male patients with childhood, adolescent, and young adult cancer: recommendations from the PanCareLIFE Consortium and the International Late Effects of Childhood Cancer Guideline Harmonization Group

Male patients with childhood, adolescent, and young adult cancer are at an increased risk for infertility if their treatment adversely affects reproductive organ function. Future fertility is a primary concern of patients and their families. Variations in clinical practice are barriers to the timely implementation of interventions that preserve fertility. As part of the PanCareLIFE Consortium, in collaboration with the International Late Effects of Childhood Cancer Guideline Harmonization Group, we reviewed the current literature and developed a clinical practice guideline for fertility preservation in male patients who are diagnosed with childhood, adolescent, and young adult cancer at age 25 years or younger, including guidance on risk assessment and available methods for fertility preservation. The Grading of Recommendations Assessment, Development and Evaluation methodology was used to grade the available evidence and to form the recommendations. Recognising the need for global consensus, this clinical practice guideline used existing evidence and international expertise to rigorously develop transparent recommendations that are easy to use to facilitate the care of male patients with childhood, adolescent, and young adult cancer who are at high risk of fertility impairment and to enhance their quality of life.

Meiotic Chromosome Synapsis and XY-Body Formation In Vitro

To achieve spermatogenesis in vitro, one of the most challenging processes to mimic is meiosis. Meiotic problems, like incomplete synapsis of the homologous chromosomes, or impaired homologous recombination, can cause failure of crossover formation and subsequent chromosome nondisjunction, eventually leading to aneuploid sperm. These meiotic events are therefore strictly monitored by meiotic checkpoints that initiate apoptosis of aberrant spermatocytes and lead to spermatogenic arrest. However, we recently found that, in vitro derived meiotic cells proceeded to the first meiotic division (MI) stage, despite displaying incomplete chromosome synapsis, no discernible XY-body and lack of crossover formation. We therefore optimized our in vitro culture system of meiosis from male germline stem cells (mGSCs) in order to achieve full chromosome synapsis, XY-body formation and meiotic crossovers. In comparison to previous culture system, the in vitro-generated spermatocytes were transferred after meiotic initiation to a second culture dish. This dish already contained a freshly plated monolayer of proliferatively inactivated immortalized Sertoli cells supporting undifferentiated mGSCs. In this way we aimed to simulate the multiple layers of germ cell types that support spermatogenesis in vivo in the testis. We found that in this optimized culture system, although independent of the undifferentiated mGSCs, meiotic chromosome synapsis was complete and XY body appeared normal. However, meiotic recombination still occurred insufficiently and only few meiotic crossovers were formed, leading to MI-spermatocytes displaying univalent chromosomes (paired sister chromatids). Therefore, considering that meiotic checkpoints are not necessarily fully functional in vitro, meiotic crossover formation should be closely monitored when mimicking gametogenesis in vitro to prevent generation of aneuploid gametes.

Tumors Widely Express Hundreds of Embryonic Germline Genes

We have recently described a class of 756 genes that are widely expressed in cancers, but are normally restricted to adult germ cells, referred to as germ cell cancer genes (GC genes). We hypothesized that carcinogenesis involves the reactivation of biomolecular processes and regulatory mechanisms that, under normal circumstances, are restricted to germline development. This would imply that cancer cells share gene expression profiles with primordial germ cells (PGCs). We therefore compared the transcriptomes of human PGCs (hPGCs) and PGC-like cells (PGCLCs) with 17,382 samples from 54 healthy somatic tissues (GTEx) and 11,003 samples from 33 tumor types (TCGA), and identified 672 GC genes, expanding the known GC gene pool by 387 genes (51%). We found that GC genes are expressed in clusters that are often expressed in multiple tumor types. Moreover, the amount of GC gene expression correlates with poor survival in patients with lung adenocarcinoma. As GC genes specific to the embryonic germline are not expressed in any adult tissue, targeting these in cancer treatment may result in fewer side effects than targeting conventional cancer/testis (CT) or GC genes and may preserve fertility. We anticipate that our extended GC dataset enables improved understanding of tumor development and may provide multiple novel targets for cancer treatment development.

ITGA6+ Human Testicular Cell Populations Acquire a Mesenchymal Rather than Germ Cell Transcriptional Signature during Long-Term Culture

Autologous spermatogonial stem cell transplantation is an experimental technique aimed at restoring fertility in infertile men. Although effective in animal models, in vitro propagation of human spermatogonia prior to transplantation has proven to be difficult. A major limiting factor is endogenous somatic testicular cell overgrowth during long-term culture. This makes the culture both inefficient and necessitates highly specific cell sorting strategies in order to enrich cultured germ cell fractions prior to transplantation. Here, we employed RNA-Seq to determine cell type composition in sorted integrin alpha-6 (ITGA6+) primary human testicular cells (n = 4 donors) cultured for up to two months, using differential gene expression and cell deconvolution analyses. Our data and analyses reveal that long-term cultured ITGA6+ testicular cells are composed mainly of cells expressing markers of peritubular myoid cells, (progenitor) Leydig cells, fibroblasts and mesenchymal stromal cells and only a limited percentage of spermatogonial cells as compared to their uncultured counterparts. These findings provide valuable insights into the cell type composition of cultured human ITGA6+ testicular cells during in vitro propagation and may serve as a basis for optimizing future cell sorting strategies as well as optimizing the current human testicular cell culture system for clinical use.

A comparative analysis of human adult testicular cells expressing stem Leydig cell markers in the interstitium, vasculature, and peritubular layer

Background

Origin of human adult Leydig cells (ALCs) is not well understood. This might be partly due to limited data available on the identification and location of human precursor and stem Leydig cells (SLCs) which hampers the study on the development of ALCs.

Objectives

The aim of the present study was to investigate whether described human (PDGFRα, NGFR) and rodent (NES, PDGFRα, THY1, NR2F2) SLC markers are expressed by a common cell population within human adult testicular interstitial cells in vivo and before and after in vitro propagation.

Materials and methods

Immunohistochemical analyses were used to identify localization of human adult testicular interstitial cells expressing described SLC markers. Next, interstitial cells were isolated and cultured. The percentage of cells expressing one or more SLC markers was determined before and after culture using flow cytometry.

Results

NR2F2 and PDGFRα were present in peritubular, perivascular, and Leydig cells, while THY1 was expressed in peritubular and perivascular cells. Although NES and NGFR were expressed in endothelial cells, co‐localization with PDGFRα was found for both in vitro, although for NGFR only after culture. All marker positive cells were able to undergo propagation in vitro.

Discussion

The partly overlap in localization and overlap in expression in human testicular cells indicate that PDGFRα, NR2F2, and THY1 are expressed within the same ALC developmental lineage from SLCs. Based on the in vitro results, this is also true for NES and after in vitro propagation for NGFR.

Conclusion

Our results that earlier described SLC markers are expressed in overlapping human interstitial cell population opens up further research strategies aiming for a better insight in the Leydig cell lineage and will be helpful for development of strategies to cure ALC dysfunction.

Infertility-Causing Haploinsufficiency Reveals TRIM28/KAP1 Requirement in Spermatogonia

Spermatogenesis relies on exquisite stem cell homeostasis, the carefully balanced self-renewal and differentiation of spermatogonial stem cells (SSCs). Disturbing this equilibrium will likely manifest through sub- or infertility, a global health issue with often idiopathic presentation. In this respect, disease phenotypes caused by haploinsufficiency of otherwise vital developmental genes are of particular interest. Here, we show that mice heterozygous for Trim28, an essential epigenetic regulator, suffer gradual testicular degeneration. Contrary to previous reports we detect Trim28 expression in spermatogonia, albeit at low levels. Further reduction through Trim28 heterozygosity increases the propensity of SSCs to differentiate at the cost of self-renewal.

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TRIM28/KAP1 haploinsufficiency causes testicular degeneration and infertility

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TRIM28/KAP1 is expressed in spermatogonia stem cell compartment

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Stem cell homeostasis in the testis is dependent on proper TRIM28/KAP1 levels

Comparing genome-scale DNA methylation and CNV marks between adult human cultured ITGA6+ testicular cells and seminomas to assess in vitro genomic stability

Autologous transplantation of spermatogonial stem cells is a promising new avenue to restore fertility in infertile recipients. Expansion of the initial spermatogonial stem cell pool through cell culturing is a necessary step to obtain enough cells for effective repopulation of the testis after transplantation. Since in vitro propagation can lead to (epi-)genetic mutations and possibly malignant transformation of the starting cell population, we set out to investigate genome-wide DNA methylation status in uncultured and cultured primary testicular ITGA6+ sorted cells and compare them with germ cell tumor samples of the seminoma subtype. Seminomas displayed a severely global hypomethylated profile, including loss of genomic imprinting, which we did not detect in cultured primary testicular ITGA6+ cells. Differential methylation analysis revealed altered regulation of gamete formation and meiotic processes in cultured primary testicular ITGA6+ cells but not in seminomas. The pivotal POU5F1 marker was hypomethylated in seminomas but not in uncultured or cultured primary testicular ITGA6+ cells, which is reflected in the POU5F1 mRNA expression levels. Lastly, seminomas displayed a number of characteristic copy number variations that were not detectable in primary testicular ITGA6+ cells, either before or after culture. Together, the data show a distinct DNA methylation patterns in cultured primary testicular ITGA6+ cells that does not resemble the pattern found in seminomas, but also highlight the need for more sensitive methods to fully exclude the presence of malignant cells after culture and to further study the epigenetic events that take place during in vitro culture.

Development and Disease-Dependent Dynamics of Spermatogonial Subpopulations in Human Testicular Tissues

Cancer therapy and conditioning treatments of non-malignant diseases affect spermatogonial function and may lead to male infertility. Data on the molecular properties of spermatogonia and the influence of disease and/or treatment on spermatogonial subpopulations remain limited. Here, we assessed if the density and percentage of spermatogonial subpopulation changes during development (n = 13) and due to disease and/or treatment (n = 18) in tissues stored in fertility preservation programs, using markers for spermatogonia (MAGEA4), undifferentiated spermatogonia (UTF1), proliferation (PCNA), and global DNA methylation (5mC). Throughout normal prepubertal testicular development, only the density of 5mC-positive spermatogonia significantly increased with age. In comparison, patients affected by disease and/or treatment showed a reduced density of UTF1-, PCNA- and 5mC-positive spermatogonia, whereas the percentage of spermatogonial subpopulations remained unchanged. As an exception, sickle cell disease patients treated with hydroxyurea displayed a reduction in both density and percentage of 5mC- positive spermatogonia. Our results demonstrate that, in general, a reduction in spermatogonial density does not alter the percentages of undifferentiated and proliferating spermatogonia, nor the establishment of global methylation. However, in sickle cell disease patients’, establishment of spermatogonial DNA methylation is impaired, which may be of importance for the potential use of this tissues in fertility preservation programs.

Human Testis Phosphoproteome Reveals Kinases as Potential Targets in Spermatogenesis and Testicular Cancer

Spermatogenesis is a complex cell differentiation process that includes marked genetic, cellular, functional and structural changes. It requires tight regulation, because disturbances in any of the spermatogenic processes would lead to fertility deficiencies as well as disorders in offspring. To increase our knowledge of signal transduction during sperm development, we carried out a large-scale identification of the phosphorylation events that occur in the human male gonad. Metal oxide affinity chromatography using TiO2 combined with LC-MS/MS was conducted to profile the phosphoproteome of adult human testes with full spermatogenesis. A total of 8187 phosphopeptides derived from 2661 proteins were identified, resulting in the most complete report of human testicular phosphoproteins to date. Phosphorylation events were enriched in proteins functionally related to spermatogenesis, as well as to highly active processes in the male gonad, such as transcriptional and translational regulation, cytoskeleton organization, DNA packaging, cell cycle and apoptosis. Moreover, 174 phosphorylated kinases were identified. The most active human protein kinases in the testis were predicted both by the number of phosphopeptide spectra identified and the phosphorylation status of the kinase activation loop. The potential function of cyclin-dependent kinase 12 (CDK12) and p21-activated kinase 4 (PAK4) has been explored by in silico, protein-protein interaction analysis, immunodetection in testicular tissue, and a functional assay in a human embryonal carcinoma cell line. The colocalization of CDK12 with Golgi markers suggests a potential crucial role of this protein kinase during sperm formation. PAK4 has been found expressed in human spermatogonia, and a role in embryonal carcinoma cell response to apoptosis has been observed. Together, our protein discovery analysis confirms that phosphoregulation by protein kinases is highly active in sperm differentiation and opens a window to detailed characterization and validation of potential targets for the development of drugs modulating male fertility and tumor behavior.

TorsinA Is Functionally Associated with Spermatogenesis

TorsinA is a member of the AAA+ superfamily of adenosine triphosphatases. These AAA+ proteins have numerous biological functions, including vesicle fusion, cytoskeleton dynamics, intracellular trafficking, protein folding, and degradation as well as organelle biogenesis. Of particular interest is torsinA, which is mainly located in the endoplasmic reticulum (ER) and nuclear envelope (NE). Interestingly, mutations in the TOR1A gene (the gene encoding torsinA) are associated with DYT1 dystonia and with the preferential localization of mutated torsinA at the NE, where it is associated with lamina-associated polypeptide 1. A bioinformatics study of the torsinA interactome revealed reproductive processes to be highly relevant, as proteins in this class were found to interact with the former. Interestingly, the torsin protein family had never been previously described to be associated with the mammalian spermatogenic process. Histological staining of torsinA in human testis tissue revealed a granular cytoplasmic localization in mid- and late spermatocytes. We further sought to understand this newly discovered expression of torsinA in the meiotic phase of human spermatogenesis by studying its specific subcellular distribution. TorsinA is not present in the ER as commonly described. The proposal that torsinA might relocate to the pro-acrosomal vesicles in the Golgi apparatus is discussed.

The risk of TESE-induced hypogonadism: a systematic review and meta-analysis

BACKGROUND

Testicular sperm extraction (TESE) is a surgical procedure to retrieve spermatozoa from the testes of men with azoospermia to help them achieve biological parenthood. Although effective, the surgical procedure is not without complications and haematoma, devascularization, inflammation and a decrease in testosterone levels have been described as such. The prevalence and duration of hypogonadism and associated symptoms after TESE have not been studied systematically.

OBJECTIVE AND RATIONALE

In this systematic review we addressed the following research questions: Are serum testosterone levels decreased after TESE and, if so, do these levels recover over time? What is the prevalence of symptoms and signs related to hypogonadism after TESE and are they related to testosterone levels?

SEARCH METHODS

We searched the databases Pubmed and Embase from 1 January 1993 to 26 June 2017. We combined subject headings with terms in title and/or abstract for participants, intervention and outcomes. We included all studies that reported on TESE, regardless of the specific technique used, that measured testosterone and/or LH, and/or had information on signs or symptoms related to hypogonadism as defined by hypogonadism guidelines. An additional inclusion criterion was that studies described these measurements both before and after TESE. The quality of the included studies was assessed using the Risk Of Bias In Non-randomized Studies-of Interventions tool.

OUTCOMES

We identified 15 studies reporting on total testosterone levels of which five studies also reported on testicular volume and one study on erectile dysfunction. Men with Klinefelter syndrome and men with non-obstructive azoospermia had the strongest decrease in total testosterone levels 6 months after TESE, with a mean decrease of 4.1 and 2.7 nmol/l, respectively, which recovered again to baseline levels 26 and 18 months after TESE, respectively. At 6 months after TESE, some studies reported serum total testosterone concentrations below a cut-off value of 12 nmol/l, where symptoms and signs related to hypogonadism may appear. Furthermore, an increased prevalence of erectile dysfunction related to decreased total testosterone levels 6 months after TESE was reported. Also, in some men a decrease in testicular volume was reported. However, it is not clear if this is related to low testosterone levels.

WIDER IMPLICATIONS

The transient, but statistically significant, decrease in total testosterone levels indicates that men are at risk of developing a temporary hypogonadism after TESE, but there is insufficient evidence for whether patients actually experience clinical symptoms in case of decreased serum testosterone levels. To be able to properly counsel TESE patients, more large-scale monitoring on signs and symptoms of hypogonadism, in combination with testosterone measurements, needs to be performed in men undergoing TESE.

A practical blueprint to systematically study life-long health consequences of novel medically assisted reproductive treatments

In medicine, safety and efficacy are the two pillars on which the implementation of novel treatments rest. To protect the patient from unnecessary or unsafe treatments, usually, a stringent path of (pre) clinical testing is followed before a treatment is introduced into routine patient care. However, in reproductive medicine several techniques have been clinically introduced without elaborate preclinical studies. Moreover, novel reproductive techniques may harbor safety risks not only for the patients undergoing treatment, but also for the offspring conceived through these techniques. If preclinical (animal) studies were performed, efficacy and functionality the upper hand. When a new medically assisted reproduction (MAR) treatment was proven effective (i.e. if it resulted in live birth) the treatment was often rapidly implemented in the clinic. For IVF, the first study on the long-term health of IVF children was published a decade after its clinical implementation. In more recent years, prospective follow-up studies have been conducted that provided the opportunity to study the health of large groups of children derived from different reproductive techniques. Although such studies have indicated differences between children conceived through MAR and children conceived naturally, results are often difficult to interpret due to the observational nature of these studies (and the associated risk of confounding factors, e.g. subfertility of the parents), differences in definitions of clinical outcome measures, lack of uniformity in assessment protocols and heterogeneity of the underlying reasons for fertility treatment. With more novel MARs waiting at the horizon, there is a need for a framework on how to assess safety of novel reproductive techniques in a preclinical (animal) setting before they are clinically implemented. In this article, we provide a blueprint for preclinical testing of safety and health of offspring generated by novel MARs using a mouse model involving an array of tests that comprise the entire lifespan. We urge scientists to perform the proposed extensive preclinical tests for novel reproductive techniques with the goal to acquire knowledge on efficacy and the possible health effects of to-be implemented reproductive techniques to safeguard quality of novel MARs.

What is the best protocol to cryopreserve immature mouse testicular cell suspensions?

RESEARCH QUESTION

From a clinical perspective, which parameters grant optimal cryopreservation of mouse testicular cell suspensions?

DESIGN

We studied the effect of different cryopreservation rates, the addition of sugars, different vessels and the addition of an apoptotic inhibitor on the efficiency of testicular cell suspension cryopreservation. After thawing and warming, testicular cell suspensions were transplanted to recipient mice for further functional assay. After selecting the optimal cryopreservation procedure, a second experiment compared the transplantation efficiency between the selected freezing protocol and fresh testicular cell suspensions.

RESULTS

Multiple- and single-step freezing did not differ significantly in terms of recovered viable cells (RVC) (33 ± 28% and 38 ± 25%). The addition of sucrose did not result in a higher RVC (33 ± 20%). Cells frozen in vials recovered better than those frozen in straws (52 ± 20% versus 33 ± 20%; P = 0.0049). The inclusion of an apoptosis inhibitor (z-VAD[Oe]-FMK) significantly increased the RVC after thawing (61 ± 18% versus 50 ± 17%; P = 0.0480). When comparing the optimal cryopreservation procedure with fresh testicular cell suspensions, a lower RVC (63 ± 11% versus 92 ± 4%; P < 0.0001) and number of donor-derived spermatogonial stem cell colonies per testis (34.04 ± 2.34 versus 16.78 ± 7.76; P = 0.0051) were observed.

CONCLUSION

Upon freeze-thawing or vitrification-warming, and assessment of donor-derived spermatogenesis after transplantation, Dulbecco's modified Eagle's medium supplemented with 1.5M dimethyl-sulphoxide, 10% fetal calf serum and 60 µM of Z-VAD-(OMe)-FMK in vials at a freezing rate of -1°C/min was optimal.

Distinct prophase arrest mechanisms in human male meiosis

To prevent chromosomal aberrations being transmitted to the offspring, strict meiotic checkpoints are in place to remove aberrant spermatocytes. However, in about 1% of males these checkpoints cause complete meiotic arrest leading to azoospermia and subsequent infertility. Here, we unravel two clearly distinct meiotic arrest mechanisms that occur during prophase of human male meiosis. Type I arrested spermatocytes display severe asynapsis of the homologous chromosomes, disturbed XY-body formation and increased expression of the Y chromosome-encoded gene ZFY and seem to activate a DNA damage pathway leading to induction of p63, possibly causing spermatocyte apoptosis. Type II arrested spermatocytes display normal chromosome synapsis, normal XY-body morphology and meiotic crossover formation but have a lowered expression of several cell cycle regulating genes and fail to silence the X chromosome-encoded gene ZFX. Discovery and understanding of these meiotic arrest mechanisms increases our knowledge of how genomic stability is guarded during human germ cell development.

Summary: Histological examination and transcriptomic analysis of human meiosis-arrested spermatocytes reveals two prophase arrest mechanisms, each associated with distinct gene expression profiles implicating the involvement of different biological processes.

Emi2 Is Essential for Mouse Spermatogenesis

The meiotic functions of Emi2, an inhibitor of the APC/C complex, have been best characterized in oocytes where it mediates metaphase II arrest as a component of the cytostatic factor. We generated knockout mice to determine the in vivo functions of Emi2-in particular, its functions in the testis, where Emi2 is expressed at high levels. Male and female Emi2 knockout mice are viable but sterile, indicating that Emi2 is essential for meiosis but dispensable for embryonic development and mitotic cell divisions. We found that, besides regulating cell-cycle arrest in mouse eggs, Emi2 is essential for meiosis I progression in spermatocytes. In the absence of Emi2, spermatocytes arrest in early diplotene of prophase I. This arrest is associated with decreased Cdk1 activity and was partially rescued by a knockin mouse model of elevated Cdk1 activity. Additionally, we detected expression of Emi2 in spermatids and sperm, suggesting potential post-meiotic functions for Emi2.

Long-term health in recipients of transplanted in vitro propagated spermatogonial stem cells

STUDY QUESTION

Is testicular transplantation of in vitro propagated spermatogonial stem cells associated with increased cancer incidence and decreased survival rates in recipient mice?

SUMMARY ANSWER

Cancer incidence was not increased and long-term survival rate was not altered after transplantation of in vitro propagated murine spermatogonial stem cells (SSCs) in busulfan-treated recipients as compared to non-transplanted busulfan-treated controls.

WHAT IS KNOWN ALREADY

Spermatogonial stem cell autotransplantation (SSCT) is a promising experimental reproductive technique currently under development to restore fertility in male childhood cancer survivors. Most preclinical studies have focused on the proof-of-principle of the functionality and efficiency of this technique. The long-term health of recipients of SSCT has not been studied systematically.

STUDY DESIGN, SIZE, DURATION

This study was designed as a murine equivalent of a clinical prospective study design. Long-term follow-up was performed for mice who received a busulfan treatment followed by either an intratesticular transplantation of in vitro propagated enhanced green fluorescent protein (eGFP) positive SSCs (cases, n = 34) or no transplantation (control, n = 37). Using a power calculation, we estimated that 36 animals per group would be sufficient to provide an 80% power and with a 5% level of significance to demonstrate a 25% increase in cancer incidence in the transplanted group. The survival rate and cancer incidence was investigated until the age of 18 months.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Neonatal male B6D2F1 actin-eGFP transgenic mouse testis were used to initiate eGFP positive germline stem (GS) cell culture, which harbor SSCs. Six-week old male C57BL/6 J mice received a single dose busulfan treatment to deplete the testis from endogenous spermatogenesis. Half of these mice received a testicular transplantation of cultured eGFP positive GS cells, while the remainder of mice served as a control group. Mice were followed up until the age of 18 months (497-517 days post-busulfan) or sacrificed earlier due to severe discomfort or illness. Survival data were collected. To evaluate cancer incidence a necropsy was performed and tissues were collected. eGFP signal in transplanted testis and in benign and malignant lesions was assessed by standard PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

We found 9% (95% CI: 2-25%) malignancies in the transplanted busulfan-treated animals compared to 26% (95% CI: 14-45%) in the busulfan-treated control group, indicating no statistically significant difference in incidence of malignant lesions in transplanted and control mice (OR: 0.3, 95% CI: 0.1-1.1). Furthermore, none of the malignancies that arose in the transplanted animals contained eGFP signal, suggesting that they are not derived from the in vitro propagated transplanted SSCs. Mean survival time after busulfan treatment was found to be equal, with a mean survival time for transplanted animals of 478 days and 437 days for control animals (P = 0.076).

LARGE SCALE DATA

NA.

LIMITATIONS, REASONS FOR CAUTION

Although we attempted to mimic the future clinical application of SSCT in humans as close as possible, the mouse model that we used might not reflect all aspects of the future clinical setting.

WIDER IMPLICATIONS OF THE FINDINGS

The absence of an increase in cancer incidence and a decrease in survival of mice that received a testicular transplantation of in vitro propagated SSCs is reassuring in light of the future clinical application of SSCT in humans.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by KiKa (Kika86) and ZonMw (TAS 116003002). The authors report no financial or other conflict of interest relevant to the subject of this article.

Unraveling transcriptome dynamics in human spermatogenesis

Spermatogenesis is a dynamic developmental process that includes stem cell proliferation and differentiation, meiotic cell divisions and extreme chromatin condensation. Although studied in mice, the molecular control of human spermatogenesis is largely unknown. Here, we developed a protocol that enables next-generation sequencing of RNA obtained from pools of 500 individually laser-capture microdissected cells of specific germ cell subtypes from fixed human testis samples. Transcriptomic analyses of these successive germ cell subtypes reveals dynamic transcription of over 4000 genes during human spermatogenesis. At the same time, many of the genes encoding for well-established meiotic and post-meiotic proteins are already present in the pre-meiotic phase. Furthermore, we found significant cell type-specific expression of post-transcriptional regulators, including expression of 110 RNA-binding proteins and 137 long non-coding RNAs, most of them previously not linked to spermatogenesis. Together, these data suggest that the transcriptome of precursor cells already contains the genes necessary for cellular differentiation and that timely translation controlled by post-transcriptional regulators is crucial for normal development. These established transcriptomes provide a reference catalog for further detailed studies on human spermatogenesis and spermatogenic failure.

Highlighted Article: Using laser capture microscopy, a comprehensive transcriptomic dataset of well-defined and distinct germ cell subtypes based on morphology and localization in the human testis is generated.

Descriptive Analysis of LAP1 Distribution and That of Associated Proteins throughout Spermatogenesis

Spermatogenesis comprises highly complex differentiation processes. Nuclear envelope (NE) proteins have been associated with these processes, including lamins, lamina-associated polypeptide (LAP) 2 and the lamin B-receptor. LAP1 is an important NE protein whose function has not been fully elucidated, but several binding partners allow predicting putative LAP1 functions. To date, LAP1 had not been associated with spermatogenesis. In this study, LAP1 expression and cellular/subcellular localization during spermatogenesis in human and mouse testes is established for the first time. The fact that LAP1 is expressed during nuclear elongation in spermiogenesis and is located at the spermatids' centriolar pole is singularly important. LAP1 binds to members of the protein phosphatase 1 (PP1) family. Similar localization of LAP1 and PP1γ2, a testis-specific PP1 isoform, suggests a shared function for both proteins during spermiogenesis. Furthermore, this study suggests an involvement of LAP1 in manchette development and chromatin regulation possibly via interaction with acetylated α-tubulin and lamins, respectively. Taken together, the present results indicate that, by moving to the posterior pole in spermatids, LAP1 can contribute to the achievement of non-random, sperm-specific chromatin distribution, as well as modulate cellular remodeling during spermiogenesis. In addition, LAP1 seems to be associated with dynamic microtubule changes related to manchette formation and flagella development.

Spermatogonial stem cell autotransplantation and germline genomic editing: a future cure for spermatogenic failure and prevention of transmission of genomic diseases

BACKGROUND

Subfertility affects approximately 15% of all couples, and a severe male factor is identified in 17% of these couples. While the etiology of a severe male factor remains largely unknown, prior gonadotoxic treatment and genomic aberrations have been associated with this type of subfertility. Couples with a severe male factor can resort to ICSI, with either ejaculated spermatozoa (in case of oligozoospermia) or surgically retrieved testicular spermatozoa (in case of azoospermia) to generate their own biological children. Currently there is no direct treatment for azoospermia or oligozoospermia. Spermatogonial stem cell (SSC) autotransplantation (SSCT) is a promising novel clinical application currently under development to restore fertility in sterile childhood cancer survivors. Meanwhile, recent advances in genomic editing, especially the clustered regulatory interspaced short palindromic repeats-associated protein 9 (CRISPR-Cas9) system, are likely to enable genomic rectification of human SSCs in the near future.

OBJECTIVE AND RATIONALE

The objective of this review is to provide insights into the prospects of the potential clinical application of SSCT with or without genomic editing to cure spermatogenic failure and to prevent transmission of genetic diseases.

SEARCH METHODS

We performed a narrative review using the literature available on PubMed not restricted to any publishing year on topics of subfertility, fertility treatments, (molecular regulation of) spermatogenesis and SSCT, inherited (genetic) disorders, prenatal screening methods, genomic editing and germline editing. For germline editing, we focussed on the novel CRISPR-Cas9 system. We included papers written in English only.

OUTCOMES

Current techniques allow propagation of human SSCs in vitro, which is indispensable to successful transplantation. This technique is currently being developed in a preclinical setting for childhood cancer survivors who have stored a testis biopsy prior to cancer treatment. Similarly, SSCT could be used to restore fertility in sterile adult cancer survivors. In vitro propagation of SSCs might also be employed to enhance spermatogenesis in oligozoospermic men and in azoospermic men who still have functional SSCs albeit in insufficient numbers. The combination of SSCT with genomic editing techniques could potentially rectify defects in spermatogenesis caused by genomic mutations or, more broadly, prevent transmission of genomic diseases to the offspring. In spite of the promising prospects, SSCT and germline genomic editing are not yet clinically applicable and both techniques require optimization at various levels.

WIDER IMPLICATIONS

SSCT with or without genomic editing could potentially be used to restore fertility in cancer survivors to treat couples with a severe male factor and to prevent the paternal transmission of diseases. This will potentially allow these couples to have their own biological children. Technical development is progressing rapidly, and ethical reflection and societal debate on the use of SSCT with or without genomic editing is pressing.

A European perspective on testicular tissue cryopreservation for fertility preservation in prepubertal and adolescent boys

STUDY QUESTION

What clinical practices, patient management strategies and experimental methods are currently being used to preserve and restore the fertility of prepubertal boys and adolescent males?

SUMMARY ANSWER

Based on a review of the clinical literature and research evidence for sperm freezing and testicular tissue cryopreservation, and after consideration of the relevant ethical and legal challenges, an algorithm for the cryopreservation of sperm and testicular tissue is proposed for prepubertal boys and adolescent males at high risk of fertility loss.

WHAT IS KNOWN ALREADY

A known late effect of the chemotherapy agents and radiation exposure regimes used to treat childhood cancers and other non-malignant conditions in males is the damage and/or loss of the proliferating spermatogonial stem cells in the testis. Cryopreservation of spermatozoa is the first line treatment for fertility preservation in adolescent males. Where sperm retrieval is impossible, such as in prepubertal boys, or it is unfeasible in adolescents prior to the onset of ablative therapies, alternative experimental treatments such as testicular tissue cryopreservation and the harvesting and banking of isolated spermatogonial stem cells can now be proposed as viable means of preserving fertility.

STUDY DESIGN, SIZE, DURATION

Advances in clinical treatments, patient management strategies and the research methods used to preserve sperm and testicular tissue for prepubertal boys and adolescents were reviewed. A snapshot of the up-take of testis cryopreservation as a means to preserve the fertility of young males prior to December 2012 was provided using a questionnaire.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A comprehensive literature review was conducted. In addition, survey results of testis freezing practices in young patients were collated from 24 European centres and Israeli University Hospitals.

MAIN RESULTS AND THE ROLE OF CHANCE

There is increasing evidence of the use of testicular tissue cryopreservation as a means to preserve the fertility of pre- and peri-pubertal boys of up to 16 year-old. The survey results indicate that of the 14 respondents, half of the centres were actively offering testis tissue cryobanking as a means of safeguarding the future fertility of boys and adolescents as more than 260 young patients (age range less than 1 year old to 16 years of age), had already undergone testicular tissue retrieval and storage for fertility preservation. The remaining centres were considering the implementation of a tissue-based fertility preservation programme for boys undergoing oncological treatments.

LIMITATIONS, REASONS FOR CAUTION

The data collected were limited by the scope of the questionnaire, the geographical range of the survey area, and the small number of respondents.

WIDER IMPLICATIONS OF THE FINDINGS

The clinical and research questions identified and the ethical and legal issues raised are highly relevant to the multi-disciplinary teams developing treatment strategies to preserve the fertility of prepubertal and adolescent boys who have a high risk of fertility loss due to ablative interventions, trauma or genetic pre-disposition.

Prenatal undernutrition and leukocyte telomere length in late adulthood: the Dutch famine birth cohort study

BACKGROUND

Energy restriction in prenatal life has detrimental effects on later life health and longevity. Studies in rats have shown that the shortening of telomeres in key tissues plays an important role in this association.

OBJECTIVE

The aim of the current study was to investigate leukocyte telomere length in relation to prenatal famine exposure.

DESIGN

The Dutch famine birth cohort consists of 2414 term singleton men and women who were born between 1943 and 1947 in Amsterdam around the time of the famine. At a mean age of 68 y, telomere length and the percentage of short telomeres was assessed in a subsample of 131 cohort members, of whom 45 were born before the famine (control), 41 were exposed to famine during early gestation, and 45 were conceived after the famine (control). Median telomere length was determined in peripheral blood leukocytes by a high-throughput quantitative fluorescent in situ hybridization-based technology.

RESULTS

Leukocyte telomere length and the percentage of short telomeres did not differ between those exposed to famine during early gestation and those unexposed during gestation. A lower socioeconomic status at birth, frequent consumption of alcohol (specifically consumption of spirits), a history of cancer, and a lower self-reported health status were significantly associated with shorter leukocyte telomere length (all P ≤ 0.03). Currently having a job was significantly associated with a smaller percentage of short telomeres (P = 0.04).

CONCLUSION

The results of the current study suggest that prenatal exposure to famine is not associated with the shortening of telomeres in peripheral blood leukocytes at age 68 y.

Spatial and temporal expression of immunoglobulin superfamily member 1 in the rat

Loss-of-function mutations in the immunoglobulin superfamily member 1 (IGSF1) gene cause an X-linked syndrome of central hypothyroidism, macroorchidism, variable prolactin and GH deficiency, delayed pubertal testosterone rise, and obesity. To understand the pathophysiology of this syndrome, knowledge on IGSF1's place in normal development is imperative. Therefore, we investigated spatial and temporal protein and mRNA expression of IGSF1 in rats using immunohistochemistry, real-time quantitative PCR (qPCR), and in situ hybridization. We observed high levels of IGSF1 expression in the brain, specifically the embryonic and adult choroid plexus and hypothalamus (principally in glial cells), and in the pituitary gland (PIT1-lineage of GH, TSH, and PRL-producing cells). IGSF1 is also expressed in the embryonic and adult zona glomerulosa of the adrenal gland, islets of Langerhans of the pancreas, and costameres of the heart and skeletal muscle. IGSF1 is highly expressed in fetal liver, but is absent shortly after birth. In the adult testis, IGSF1 is present in Sertoli cells (epithelial stages XIII-VI), and elongating spermatids (stages X-XII). Specificity of protein expression was corroborated with Igsf1 mRNA expression in all tissues. The expression patterns of IGSF1 in the pituitary gland and testis are consistent with the pituitary hormone deficiencies and macroorchidism observed in patients with IGSF1 deficiency. The expression in the brain, adrenal gland, pancreas, liver, and muscle suggest IGSF1's function in endocrine physiology might be more extensive than previously considered.

Cryopreservation of testicular tissue before long-term testicular cell culture does not alter in vitro cell dynamics

OBJECTIVE

To assess whether testicular cell dynamics are altered during long-term culture after testicular tissue cryopreservation.

DESIGN

Experimental basic science study.

SETTING

Reproductive biology laboratory.

PATIENT(S)

Testicular tissue with normal spermatogenesis was obtained from six donors.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Detection and comparison of testicular cells from fresh and frozen tissues during long-term culture.

RESULT(S)

Human testicular cells derived from fresh (n = 3) and cryopreserved (n = 3) tissues were cultured for 2 months and analyzed with quantitative reverse-transcription polymerase chain reaction and immunofluorescence. Spermatogonia including spermatogonial stem cells (SSCs) were reliably detected by combining VASA, a germ cell marker, with UCHL1, a marker expressed by spermatogonia. The established markers STAR, ACTA2, and SOX9 were used to analyze the presence of Leydig cells, peritubular myoid cells, and Sertoli cells, respectively. No obvious differences were found between the cultures initiated from fresh or cryopreserved tissues. Single or small groups of SSCs (VASA(+)/UCHL1(+)) were detected in considerable amounts up to 1 month of culture, but infrequently after 2 months. SSCs were found attached to the feeder monolayer, which expressed markers for Sertoli cells, Leydig cells, and peritubular myoid cells. In addition, VASA(-)/UCHL1(+) cells, most likely originating from the interstitium, also contributed to this monolayer. Apart from Sertoli cells, all somatic cell types could be detected throughout the culture period.

CONCLUSION(S)

Testicular tissue can be cryopreserved before long-term culture without modifying its outcome, which encourages implementation of testicular tissue banking for fertility preservation. However, because of the limited numbers of SSCs available after 2 months, further exploration and optimization of the culture system is needed.

Genetic and epigenetic stability of human spermatogonial stem cells during long-term culture

OBJECTIVE

To determine the genetic and epigenetic stability of human spermatogonial stem cells (SSCs) during long-term culture.

DESIGN

Experimental basic science study.

SETTING

Reproductive biology laboratory.

PATIENT(S)

Cryopreserved human testicular tissue from two prostate cancer patients with normal spermatogenesis.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Testicular cells before and 50 days after culturing were subjected to ITGA6 magnetic-activated cell sorting to enrich for SSCs. Individual spermatogonia were analyzed for aneuploidies with the use of single-cell 24-chromosome screening. Furthermore, the DNA methylation statuses of the paternally imprinted genes H19, H19-DMR (differentially methylated region), and MEG3 and the maternally imprinted genes KCNQ1OT1 and PEG3 were identified by means of bisulfite sequencing.

RESULTS(S)

Aneuploidy screening showed euploidy with no chromosomal abnormalities in all cultured and most noncultured spermatogonia from both patients. The methylation assays demonstrated demethylation of the paternally imprinted genes H19, H19-DMR, and MEG3 of 11%-28%, 43%-68%, and 18%-26%, respectively, and increased methylation of the maternally imprinted genes PEG 3 and KCNQ1OT of 13%-50% and 30%-38%, respectively, during culture.

CONCLUSION(S)

In the current culture system for human SSCs propagation, genomic stability is preserved, which is important for future clinical use. Whether the observed changes in methylation status have consequences on functionality of SSCs or health of offspring derived from transplanted SSCs requires further investigation.

Enrichment of spermatogonial stem cells from long-term cultured human testicular cells

OBJECTIVE

To evaluate the degree of enrichment of spermatogonial stem cells (SSCs) from human testicular cell cultures by ITGA6+, HLA-/ITGA6+, GPR125+, and HLA-/GPR125+ magnetic-assisted cell sorting (MACS).

DESIGN

Experimental basic science study.

SETTING

Reproductive biology laboratory.

PATIENT(S)

Multiple samples of cryopreserved human testicular cells from two prostate cancer patients with normal spermatogenesis.

INTERVENTION(S)

Cultured human testicular cells subjected to four sorting strategies based on MACS and xenotransplanted to the testes of mice to determine the enrichment for SSCs.

MAIN OUTCOME MEASURE(S)

Enrichment for human spermatogonia and SSCs tested by expression analysis of spermatogonial markers ITGA6, GPR125, ZBTB16, UCHL1, and ID4 using quantitative real-time polymerase chain reaction (qPCR) and by xenotransplantation into the testes of mice, respectively.

RESULT(S)

Compared with the nonsorted cultured testicular cells, only the ITGA6+ and HLA-/GPR125+ sorted cells showed enrichment for ID4. No difference in expression of ZBTB16 and UCHL1 was observed. Xenotransplantation of the sorted cell fractions showed a 7.1-fold enrichment of SSCs with ITGA6+.

CONCLUSION(S)

Magnetic-assisted cell sorting of cultured human testicular cells using ITGA6 allows for enrichment of SSCs, which aids in further molecular characterization of cultured human SSCs and enhances testicular colonization upon transplantation in future clinical settings.

Eliminating acute lymphoblastic leukemia cells from human testicular cell cultures: a pilot study

OBJECTIVE

To study whether acute lymphoblastic leukemia (ALL) cells survive in a human testicular cell culture system.

DESIGN

Experimental laboratory study.

SETTING

Reproductive biology laboratory, academic medical center.

PATIENT(S)

Acute lymphoblastic leukemia cells from three patients and testicular cells from three other patients.

INTERVENTION(S)

Acute lymphoblastic leukemia cells were cultured alone or in combination with testicular cells, at various concentrations, in a system that has recently been developed to propagate human spermatogonial stem cells.

MAIN OUTCOME MEASURE(S)

Viability of ALL and testicular cells during culture was evaluated by flow cytometry using markers for live/dead cells. Furthermore, the presence of ALL cells among testicular cells was determined by highly sensitive (1:10,000 to 1:100,000 cells) patient-specific antigen-receptor minimal residual disease polymerase chain reaction. The presence of spermatogonia at the end of culture was determined by reverse transcription-polymerase chain reaction for ZBTB16, UCHL1, and GPR125.

RESULT(S)

The ALL cells cultured separately did not survive beyond 14 days of culture. When cultured together with testicular cells, even at extremely high initial concentrations (40% ALL cells), ALL cells were undetectable beyond 26 days of culture. Reverse transcription-polymerase chain reaction confirmed the presence of spermatogonia at the end of the culture period.

CONCLUSION(S)

Our pilot study shows that the described testicular cell culture system not only allows for efficient propagation of spermatogonial stem cells but also eliminates contaminating ALL cells.

Assuring safety without animal testing: the case for the human testis in vitro

From 15 to 17 June 2011, a dedicated workshop was held on the subject of in vitro models for mammalian spermatogenesis and their applications in toxicological hazard and risk assessment. The workshop was sponsored by the Dutch ASAT initiative (Assuring Safety without Animal Testing), which aims at promoting innovative approaches toward toxicological hazard and risk assessment on the basis of human and in vitro data, and replacement of animal studies. Participants addressed the state of the art regarding human and animal evidence for compound mediated testicular toxicity, reviewed existing alternative assay models, and brainstormed about future approaches, specifically considering tissue engineering. The workshop recognized the specific complexity of testicular function exemplified by dedicated cell types with distinct functionalities, as well as different cell compartments in terms of microenvironment and extracellular matrix components. This complexity hampers quick results in the realm of alternative models. Nevertheless, progress has been achieved in recent years, and innovative approaches in tissue engineering may open new avenues for mimicking testicular function in vitro. Although feasible, significant investment is deemed essential to be able to bring new ideas into practice in the laboratory. For the advancement of in vitro testicular toxicity testing, one of the most sensitive end points in regulatory reproductive toxicity testing, such an investment is highly desirable.

Studying nonobstructive azoospermia in cystinosis: histologic examination of testes and epididymis and sperm analysis in a Ctns⁻/⁻ mouse model

OBJECTIVE

To study the pathogenesis of male infertility in cystinosis due to nonobstructive azoospermia, using a Ctns(-/-) mouse model.

DESIGN

Observational case-control study.

SETTING

Academic research laboratory.

ANIMAL(S)

Male C57BL/6 Ctns(-/-) mice were compared with C57BL/6 wild-type (wt) mice.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Fertility was studied using litter size (n = 3 vs. n = 2). After animals were sacrificed, testes, epididymis, and vas deferens were removed for testicular cystine measurements (n = 5 vs. n = 6), histologic studies (n = 3 vs. n = 3), and sperm analysis (n = 3 vs. n = 3).

RESULT(S)

Mean testicular cystine content was significantly higher in Ctns(-/-) mice compared with wt mice (26.6 ± 1.22 vs. 0.1 ± 0.01 nmol cystine/mg protein). Testes of Ctns(-/-) mice had lower weight compared with wt mice (0.096 ± 0.009 g vs. 0.112 ± 0.004 g), but mice fertility was similar (litter size 6.6 ± 1.4 vs. 6.3 ± 2.6 pups). Neither histologic nor sperm abnormalities were found.

CONCLUSION(S)

The Ctns(-/-) mouse model generated on C57BL/6 background is not suitable for clarifying the pathogenesis of male infertility in cystinosis. The etiology of nonobstructive azoospermia in these patients remains unclear.

Molecular control of rodent spermatogenesis

Spermatogenesis is a complex developmental process that ultimately generates mature spermatozoa. This process involves a phase of proliferative expansion, meiosis, and cytodifferentiation. Mouse models have been widely used to study spermatogenesis and have revealed many genes and molecular mechanisms that are crucial in this process. Although meiosis is generally considered as the most crucial phase of spermatogenesis, mouse models have shown that pre-meiotic and post-meiotic phases are equally important. Using knowledge generated from mouse models and in vitro studies, the current review provides an overview of the molecular control of rodent spermatogenesis. Finally, we briefly relate this knowledge to fertility problems in humans and discuss implications for future research. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Gene copy number reduction in the azoospermia factor c (AZFc) region and its effect on total motile sperm count

The azoospermia factor c (AZFc) region harbors multi-copy genes that are expressed in the testis. Deletions of the AZFc region lead to reduced copy numbers of these genes. Four (partial) AZFc deletions have been described of which the b2/b4 and gr/gr deletions affect semen quality. In most studies, (partial) AZFc deletions are identified and characterized using plus/minus sequence site tag (STS) polymerase chain reaction (PCR). However, secondary duplications increase the gene copy number without re-introducing the STS boundary marker. Consequently, the actual copy number of AZFc genes cannot be determined via STS PCR. In the current study, we first set out to determine by quantitative real-time PCR the actual copy number of all AZFc genes in men with (partial) AZFc deletions based on STS PCR. We then analyzed whether reduced gene copy numbers of each AZFc gene family were associated with reduced total motile sperm count (TMC), regardless of the type of deletion. We screened 840 men and identified 31 unrelated men with (partial) deletions of AZFc based on STS PCR. Of these 31 men, 6 men (19%) had one or more secondary duplications. For all AZFc genes, we found an association between a reduction in the copy number of each individual AZFc gene and reduced TMC. In gr/gr-deleted men, restoration of reduced gene copy numbers restored their TMC to normal values. Our findings suggest that the gene content of the AZFc region has been preserved throughout evolution through a dosage effect of the AZFc genes on TMC safeguarding male fertility.

A distinct expression pattern in mammalian testes indicates a conserved role for NANOG in spermatogenesis

BACKGROUND

NANOG is a key player in pluripotency and its expression is restricted to pluripotent cells of the inner cell mass, the epiblast and to primordial germ cells. Spermatogenesis is closely associated with pluripotency, because through this process highly specialized sperm cells are produced that contribute to the formation of totipotent zygotes. Nevertheless, it is unknown if NANOG plays a role in this process.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study, NANOG expression was examined in testes of various mammals, including mouse and human. Nanog mRNA and NANOG protein were detected by RT-PCR, immunohistochemistry, and western blotting. Furthermore, eGFP expression was detected in the testis of a transgenic Nanog eGFP-reporter mouse. Surprisingly, although NANOG expression has previously been associated with undifferentiated cells with stem cell potential, expression in the testis was observed in pachytene spermatocytes and in the first steps of haploid germ cell maturation (spermiogenesis). Weak expression in type A spermatogonia was also observed.

CONCLUSIONS

The findings of the current study strongly suggest a conserved role for NANOG in meiotic and post-meiotic stages of male germ cell development.

Propagation of human spermatogonial stem cells in vitro

CONTEXT

Young boys treated with high-dose chemotherapy are often confronted with infertility once they reach adulthood. Cryopreserving testicular tissue before chemotherapy and autotransplantation of spermatogonial stem cells at a later stage could theoretically allow for restoration of fertility.

OBJECTIVE

To establish in vitro propagation of human spermatogonial stem cells from small testicular biopsies to obtain an adequate number of cells for successful transplantation.

DESIGN, SETTING, AND PARTICIPANTS

Study performed from April 2007 to July 2009 using testis material donated by 6 adult men who underwent orchidectomy as part of prostate cancer treatment. Testicular cells were isolated and cultured in supplemented StemPro medium; germline stem cell clusters that arose were subcultured on human placental laminin-coated dishes in the same medium. Presence of spermatogonia was determined by reverse transcriptase polymerase chain reaction and immunofluorescence for spermatogonial markers. To test for the presence of functional spermatogonial stem cells in culture, xenotransplantation to testes of immunodeficient mice was performed, and migrated human spermatogonial stem cells after transplantation were detected by COT-1 fluorescence in situ hybridization. The number of colonized spermatogonial stem cells transplanted at early and later points during culture were counted to determine propagation.

MAIN OUTCOME MEASURES

Propagation of spermatogonial stem cells over time.

RESULTS

Testicular cells could be cultured and propagated up to 15 weeks. Germline stem cell clusters arose in the testicular cell cultures from all 6 men and could be subcultured and propagated up to 28 weeks. Expression of spermatogonial markers on both the RNA and protein level was maintained throughout the entire culture period. In 4 of 6 men, xenotransplantation to mice demonstrated the presence of functional spermatogonial stem cells, even after prolonged in vitro culture. Spermatogonial stem cell numbers increased 53-fold within 19 days in the testicular cell culture and increased 18,450-fold within 64 days in the germline stem cell subculture.

CONCLUSION

Long-term culture and propagation of human spermatogonial stem cells in vitro is achievable.

Y chromosome TSPY copy numbers and semen quality

OBJECTIVE

To determine whether variation in testis-specific protein Y-encoded (TSPY) gene copy number affects semen quality.

DESIGN

Nested case-control study.

SETTING

University hospital.

PATIENT(S)

From a consecutive cohort of 1,016 male partners of subfertile couples, unselected for sperm counts, we selected as cases 100 men with the lowest total number of progressively motile sperm (TMC) and as controls, 100 men with the highest total number of progressively motile sperm.

INTERVENTION(S)

Quantitative real-time polymerase chain reaction (PCR) and Southern blot to determine TSPY copy number.

MAIN OUTCOME MEASURE(S)

TSPY copy number.

RESULT(S)

The quantitative PCR method showed excellent agreement with the Southern blot analysis. Cases had a median TSPY copy number of 35 (range 20-73), whereas controls had a median TSPY copy number of 34 (range 26-76). This difference was not statistically significant.

CONCLUSION(S)

We found no association between TSPY copy numbers and severe spermatogenic failure. The observed variation in TSPY copy number therefore appears to have no functional consequences for semen quality.

Stra8 and its inducer, retinoic acid, regulate meiotic initiation in both spermatogenesis and oogenesis in mice

In eukaryotes, diploid cells give rise to haploid cells via meiosis, a program of two cell divisions preceded by one round of DNA replication. Although key molecular components of the meiotic apparatus are highly conserved among eukaryotes, the mechanisms responsible for initiating the meiotic program have diverged substantially among eukaryotes. This raises a related question in animals with two distinct sexes: Within a given species, are similar or different mechanisms of meiotic initiation used in the male and female germ lines? In mammals, this question is underscored by dramatic differences in the timing of meiotic initiation in males and females. Stra8 is a vertebrate-specific, cytoplasmic factor expressed by germ cells in response to retinoic acid. We previously demonstrated that Stra8 gene function is required for meiotic initiation in mouse embryonic ovaries. Here we report that, on an inbred C57BL/6 genetic background, the same factor is also required for meiotic initiation in germ cells of juvenile mouse testes. In juvenile C57BL/6 males lacking Stra8 gene function, the early mitotic development of germ cells appears to be undisturbed. However, these cells then fail to undergo the morphological changes that define meiotic prophase, and they do not display the molecular hallmarks of meiotic chromosome cohesion, synapsis and recombination. We conclude that, in mice, Stra8 regulates meiotic initiation in both spermatogenesis and oogenesis. Taken together with previous observations, our present findings indicate that, in both the male and female germ lines, meiosis is initiated through retinoic acid induction of Stra8.

Expression of the pluripotency marker UTF1 is restricted to a subpopulation of early A spermatogonia in rat testis

The population of early A spermatogonia includes stem cells that possess spermatogonial stem cell properties. Recent reports suggest that these cells have the ability to regain pluripotent properties. Here, we show that expression of the pluripotency marker undifferentiated embryonic cell transcription factor 1 (UTF1) is restricted to distinct germ cells within the testis. In embryonic and neonatal testes, all gonocytes were found to strongly express UTF1. During further testicular development, expression of UTF1 was restricted to a subset of A spermatogonia and with the increase in age the number of cells expressing UTF1 decreased even more. Ultimately, in the adult rat testis, only a small subset of the A spermatogonia expressed UTF1. Remarkably, even in testes of vitamin A-deficient rats, in which the early A spermatogonia (A(s), A(pr), and A(al)) are the only type of spermatogonia, only a subset of the spermatogonia expressed UTF1. In the adult rat testis, expression of UTF1 is restricted to a subpopulation of the ZBTB16 (PLZF)-positive early A spermatogonia. Furthermore, the observed distribution pattern of UTF1-expressing cells over the different stages of the cycle of the seminiferous epithelium suggests that the expression of UTF1 is restricted to those A(s), A(pr), and short chains of A(al) spermatogonia that are in the undifferentiated state and therefore maintain the ability to differentiate into A1 spermatogonia in the next round of the epithelial cycle or possibly even in other directions when they are taken out of their testicular niche.

Spermatogonial stem cells: characteristics and experimental possibilities

The continuation of the spermatogenic process throughout life relies on a proper regulation of self-renewal and differentiation of the spermatogonial stem cells. These are single cells situated on the basal membrane of the seminiferous epithelium. Only 0.03% of all germ cells are spermatogonial stem cells. They are the only cell type that can repopulate and restore fertility to congenitally infertile recipient mice following transplantation. Although numerous expression markers have been helpful in isolating and enriching spermatogonial stem cells, such as expression of THY-1 and GFRalpha-1 and absence of c-kit, no specific marker for this cell type has yet been identified. Much effort has been put into developing a protocol for the maintenance of spermatogonial cells in vitro. Recently, coculture systems of testicular cells on various feeder cells have made it possible to culture spermatogonial stem cells for a long period of time, as was demonstrated by the transplantation assay. Even expansion of testicular cells, including the spermatogonial stem cells, has been achieved. In these culture systems, hormones and growth factors are investigated for their role in the process of proliferation of spermatogonial stem cells. At the moment the best culture system known still consists of a mixture of testicular cells with about 1.33% spermatogonial stem cells. Recently pure SV40 large T immortalized spermatogonial stem cell lines have been established. These c-kit-negative cell lines did not show any differentiation in vitro or in vivo. A telomerase immortalized c-kit-positive spermatogonial cell line has been established that was able to differentiate in vitro. Spermatocytes and even spermatids were formed. However, spermatogonial stem cell activity by means of the transplantation assay was not tested for this cell line. Both the primary long-term cultures and immortalized cell lines have represented a major step forward in investigating the regulation of spermatogonial self-renewal and differentiation, and will be useful for identifying specific molecular markers.

LY6A/E (SCA-1) expression in the mouse testis

Recently, it was found by two research groups that LY6A, known widely in the stem cell community as stem cell antigen-1 or SCA-1, is expressed on testicular side population (SP) cells. Whether these SP cells are spermatogonial stem cells is a point of disagreement and, therefore, the identity of the LY6A-positive cells as well. We studied the expression pattern of LY6A in testis by immunohistochemistry and found it to be expressed in the interstitial tissue on peritubular myoid, endothelial, and spherical-shaped peritubular mesenchymal cells. To address the question whether LY6A has a function in spermatogenesis or testis development, we studied the testis of Ly6a(-/-) mice (allele Ly6a(tm1Pmf)). We found no morphological abnormalities or differences in numbers of spermatogonia, spermatocytes, Leydig cells, or macrophages in relation to the number of Sertoli cells. Therefore, we conclude that LY6A expression does not influence testis development or spermatogenesis and that spermatogonial stem cells are LY6A negative.