Autonomous transposons tune their sequences to ensure somatic suppression

Transposable elements (TEs) are a major constituent of human genes, occupying approximately half of the intronic space. During pre-messenger RNA synthesis, intronic TEs are transcribed along with their host genes but rarely contribute to the final mRNA product because they are spliced out together with the intron and rapidly degraded. Paradoxically, TEs are an abundant source of RNA-processing signals through which they can create new introns1, and also functional2 or non-functional chimeric transcripts3. The rarity of these events implies the existence of a resilient splicing code that is able to suppress TE exonization without compromising host pre-mRNA processing. Here we show that SAFB proteins protect genome integrity by preventing retrotransposition of L1 elements while maintaining splicing integrity, via prevention of the exonization of previously integrated TEs. This unique dual role is possible because of L1's conserved adenosine-rich coding sequences that are bound by SAFB proteins. The suppressive activity of SAFB extends to tissue-specific, giant protein-coding cassette exons, nested genes and Tigger DNA transposons. Moreover, SAFB also suppresses LTR/ERV elements in species in which they are still active, such as mice and flies. A significant subset of splicing events suppressed by SAFB in somatic cells are activated in the testis, coinciding with low SAFB expression in postmeiotic spermatids. Reminiscent of the division of labour between innate and adaptive immune systems that fight external pathogens, our results uncover SAFB proteins as an RNA-based, pattern-guided, non-adaptive defence system against TEs in the soma, complementing the RNA-based, adaptive Piwi-interacting RNA pathway of the germline.

WDFY1, a WD40 repeat protein, is not essential for spermatogenesis and male fertility in mice

The mouse WD repeat and FYVE domain containing 1 (Wdfy1) gene is located in chromosome 1qC4 and spans over 73.7 kilobases. It encodes a protein of 410-amino acid protein that shares 97.8% amino acid sequence identity with the human WDFY1 protein. However, the expression pattern of WDFY1 in reproductive organs and its function in male fertility remain unknown. In this study, we generated transgenic mice expressing FLAG-Wdfy1-mCherry cDNA driven by the Wdfy1 promoter to clarify the expression of WDFY1. The results showed that WDFY1 is highly expressed in mouse testes and located in the cytoplasm of late pachytene spermatocytes to elongated spermatids. Interestingly, the global Wdfy1 knockout (KO) male mice displayed normal growth, development, and fertility. Further histological analysis of Wdfy1 knockout mouse testes revealed that all spermatogenic cells are present in Wdfy1 KO seminiferous tubules. Together, our data demonstrate that WDFY1 is dispensable for mouse spermatogenesis and male fertility.

Differential Effects of Low and High Radiation Dose Rates on Mouse Spermatogenesis

The adverse effects of radiation are proportional to the total dose and dose rate. We aimed to investigate the effects of radiation dose rate on different organs in mice. The mice were subjected to low dose rate (LDR, ~3.4 mGy/h) and high dose rate (HDR, ~51 Gy/h) radiation. LDR radiation caused severe tissue toxicity, as observed in the histological analysis of testis. It adversely influenced sperm production, including sperm count and motility, and induced greater sperm abnormalities. The expression of markers of early stage spermatogonial stem cells, such as Plzf, c-Kit, and Oct4, decreased significantly after LDR irradiation, compared to that following exposure of HDR radiation, in qPCR analysis. The compositional ratios of all stages of spermatogonia and meiotic cells, except round spermatid, were considerably reduced by LDR in FACS analysis. Therefore, LDR radiation caused more adverse testicular damage than that by HDR radiation, contrary to the response observed in other organs. Therefore, the dose rate of radiation may have differential effects, depending on the organ; it is necessary to evaluate the effect of radiation in terms of radiation dose, dose rate, organ type, and other conditions.

Direct reprogramming of human Sertoli cells into male germline stem cells with the self-renewal and differentiation potentials via overexpressing DAZL/DAZ2/BOULE genes

We propose a new concept that human somatic cells can be converted to become male germline stem cells by the defined factors. Here, we demonstrated that the overexpression of DAZL, DAZ2, and BOULE could directly reprogram human Sertoli cells into cells with the characteristics of human spermatogonial stem cells (SSCs), as shown by their similar transcriptomes and proteomics with human SSCs. Significantly, human SSCs derived from human Sertoli cells colonized and proliferated in vivo, and they could differentiate into spermatocytes and haploid spermatids in vitro. Human Sertoli cell-derived SSCs excluded Y chromosome microdeletions and assumed normal chromosomes. Collectively, human somatic cells could be converted directly to human SSCs with the self-renewal and differentiation potentials and high safety. This study is of unusual significance, because it provides an effective approach for reprogramming human somatic cells into male germ cells and offers invaluable male gametes for treating male infertility.

RNA-binding protein Maca is crucial for gigantic male fertility factor gene expression, spermatogenesis, and male fertility, in Drosophila

During spermatogenesis, the process in which sperm for fertilization are produced from germline cells, gene expression is spatiotemporally highly regulated. In Drosophila, successful expression of extremely large male fertility factor genes on Y-chromosome spanning some megabases due to their gigantic intron sizes is crucial for spermatogenesis. Expression of such extremely large genes must be challenging, but the molecular mechanism that allows it remains unknown. Here we report that a novel RNA-binding protein Maca, which contains two RNA-recognition motifs, is crucial for this process. maca null mutant male flies exhibited a failure in the spermatid individualization process during spermatogenesis, lacked mature sperm, and were completely sterile, while maca mutant female flies were fully fertile. Proteomics and transcriptome analyses revealed that both protein and mRNA abundance of the gigantic male fertility factor genes kl-2, kl-3, and kl-5 (kl genes) are significantly decreased, where the decreases of kl-2 are particularly dramatic, in maca mutant testes. Splicing of the kl-3 transcripts was also dysregulated in maca mutant testes. All these physiological and molecular phenotypes were rescued by a maca transgene in the maca mutant background. Furthermore, we found that in the control genetic background, Maca is exclusively expressed in spermatocytes in testes and enriched at Y-loop A/C in the nucleus, where the kl-5 primary transcripts are localized. Our data suggest that Maca increases transcription processivity, promotes successful splicing of gigantic introns, and/or protects transcripts from premature degradation, of the kl genes. Our study identified a novel RNA-binding protein Maca that is crucial for successful expression of the gigantic male fertility factor genes, spermatogenesis, and male fertility.

Meiosis-specific ZFP541 repressor complex promotes developmental progression of meiotic prophase towards completion during mouse spermatogenesis

During spermatogenesis, meiosis is accompanied by a robust alteration in gene expression and chromatin status. However, it remains elusive how the meiotic transcriptional program is established to ensure completion of meiotic prophase. Here, we identify a protein complex that consists of germ-cell-specific zinc-finger protein ZFP541 and its interactor KCTD19 as the key transcriptional regulators in mouse meiotic prophase progression. Our genetic study shows that ZFP541 and KCTD19 are co-expressed from pachytene onward and play an essential role in the completion of the meiotic prophase program in the testis. Furthermore, our ChIP-seq and transcriptome analyses identify that ZFP541 binds to and suppresses a broad range of genes whose function is associated with biological processes of transcriptional regulation and covalent chromatin modification. The present study demonstrates that a germ-cell specific complex that contains ZFP541 and KCTD19 promotes the progression of meiotic prophase towards completion in male mice, and triggers the reconstruction of the transcriptional network and chromatin organization leading to post-meiotic development.

HDAC3 controls male fertility through enzyme-independent transcriptional regulation at the meiotic exit of spermatogenesis

The transition from meiotic spermatocytes to postmeiotic haploid germ cells constitutes an essential step in spermatogenesis. The epigenomic regulatory mechanisms underlying this transition remain unclear. Here, we find a prominent transcriptomic switch from the late spermatocytes to the early round spermatids during the meiotic-to-postmeiotic transition, which is associated with robust histone acetylation changes across the genome. Among histone deacetylases (HDACs) and acetyltransferases, we find that HDAC3 is selectively expressed in the late meiotic and early haploid stages. Three independent mouse lines with the testis-specific knockout of HDAC3 show infertility and defects in meiotic exit with an arrest at the late stage of meiosis or early stage of round spermatids. Stage-specific RNA-seq and histone acetylation ChIP-seq analyses reveal that HDAC3 represses meiotic/spermatogonial genes and activates postmeiotic haploid gene programs during meiotic exit, with associated histone acetylation alterations. Unexpectedly, abolishing HDAC3 catalytic activity by missense mutations in the nuclear receptor corepressor (NCOR or SMRT) does not cause infertility, despite causing histone hyperacetylation as HDAC3 knockout, demonstrating that HDAC3 enzyme activity is not required for spermatogenesis. Motif analysis of the HDAC3 cistrome in the testes identified SOX30, which has a similar spatiotemporal expression pattern as HDAC3 during spermatogenesis. Depletion of SOX30 in the testes abolishes the genomic recruitment of the HDAC3 to the binding sites. Collectively, these results establish the SOX30/HDAC3 signaling as a key regulator of the transcriptional program in a deacetylase-independent manner during the meiotic-to-postmeiotic transition in spermatogenesis.

Mitochondrial fission factor (Mff) is required for organization of the mitochondrial sheath in spermatids

BACKGROUND

Mitochondrial fission counterbalances fusion to maintain organelle morphology, but its role during development remains poorly characterized. Mammalian spermatogenesis is a complex developmental process involving several drastic changes to mitochondrial shape and organization. Mitochondria are generally small and spherical in spermatogonia, elongate during meiosis, and fragment in haploid round spermatids. Near the end of spermatid maturation, small mitochondrial spheres line the axoneme, elongate, and tightly wrap around the midpiece to form the mitochondrial sheath, which is critical for fueling flagellar movements. It remains unclear how these changes in mitochondrial morphology are regulated and how they affect sperm development.

METHODS

We used genetic ablation of Mff (mitochondrial fission factor) in mice to investigate the role of mitochondrial fission during mammalian spermatogenesis.

RESULTS

Our analysis indicates that Mff is required for mitochondrial fragmentation in haploid round spermatids and for organizing mitochondria in the midpiece in elongating spermatids. In Mff mutant mice, round spermatids have aberrantly elongated mitochondria that often show central constrictions, suggestive of failed fission events. In elongating spermatids and spermatozoa, mitochondrial sheaths are disjointed, containing swollen mitochondria with large gaps between organelles. These mitochondrial abnormalities in Mff mutant sperm are associated with reduced respiratory chain Complex IV activity, aberrant sperm morphology and motility, and reduced fertility.

CONCLUSIONS

Mff is required for organization of the mitochondrial sheath in mouse sperm.

GENERAL SIGNIFICANCE

Mitochondrial fission plays an important role in regulating mitochondrial organization during a complex developmental process.

The tumor suppressor archipelago E3 ligase is required for spermatid differentiation in Drosophila testis

The human orthologue of the tumor suppressor protein FBW7 is encoded by the Drosophila archipelago (ago) gene. Ago is an F-box protein that gives substrate specificity to its SCF ubiquitin ligase complex. It has a central role in multiple biological processes in a tissue-specific manner such as cell proliferation, cellular differentiation, hypoxia-induced gene expression. Here we present a previously unknown tissue-specific role of Ago in spermatid differentiation. We identified a classical mutant of ago which is semi-lethal and male-sterile. During the characterization of ago function in testis, we found that ago plays role in spermatid development, following meiosis. We confirmed spermatogenesis defects by silencing ago by RNAi in testes. The ago mutants show multiple abnormalities in elongating and elongated spermatids, including aberration of the cyst morphology, malformed mitochondrial structures, and individualization defects. Additionally, we determined the subcellular localization of Ago protein with mCherry-Ago transgene in spermatids. Our findings highlight the potential roles of Ago in different cellular processes of spermatogenesis, like spermatid individualization, and regulation of mitochondrial morphology.

KIF15 supports spermatogenesis via its effects on Sertoli cell microtubule, actin, vimentin, and septin cytoskeletons

Throughout spermatogenesis, cellular cargoes including haploid spermatids are required to be transported across the seminiferous epithelium, either toward the microtubule (MT) plus (+) end near the basement membrane at stage V, or to the MT minus (-) end near the tubule lumen at stages VI to VIII of the epithelial cycle. Furthermore, preleptotene spermatocytes, differentiated from type B spermatogonia, are transported across the Sertoli cell blood-testis barrier (BTB) to enter the adluminal compartment. Few studies, however, have been conducted to explore the function of MT-dependent motor proteins to support spermatid transport during spermiogenesis. Herein, we examined the role of MT-dependent and microtubule plus (+) end-directed motor protein kinesin 15 (KIF15) in the testis. KIF15 displayed a stage-specific expression across the seminiferous epithelium, associated with MTs, and appeared as aggregates on the MT tracks that aligned perpendicular to the basement membrane and laid across the entire epithelium. KIF15 also tightly associated with apical ectoplasmic specialization, displaying strict stage-specific distribution, apparently to support spermatid transport across the epithelium. We used a loss-of-function approach by RNAi to examine the role of KIF15 in Sertoli cell epithelium in vitro to examine its role in cytoskeletal-dependent Sertoli cell function. It was noted that KIF15 knockdown by RNAi that reduced KIF15 expression by ~70% in Sertoli cells with an established functional tight junction barrier impeded the barrier function. This effect was mediated through remarkable changes in the cytoskeletal organization of MTs, but also actin-, vimentin-, and septin-based cytoskeletons, illustrating that KIF15 exerts its regulatory effects well beyond microtubules.

Isolation of Murine Spermatogenic Cells using a Violet-Excited Cell-Permeable DNA Binding Dye

Isolation of meiotic spermatocytes is essential to investigate molecular mechanisms underlying meiosis and spermatogenesis. Although there are established cell isolation protocols using Hoechst 33342 staining in combination with fluorescence-activated cell sorting, it requires cell sorters equipped with an ultraviolet laser. Here we describe a cell isolation protocol using the DyeCycle Violet (DCV) stain, a low cytotoxicity DNA binding dye structurally similar to Hoechst 33342. DCV can be excited by both ultraviolet and violet lasers, which improves the flexibility of equipment choice, including a cell sorter not equipped with an ultraviolet laser. Using this protocol, one can isolate three live-cell subpopulations in meiotic prophase I, including leptotene/zygotene, pachytene, and diplotene spermatocytes, as well as post-meiotic round spermatids. We also describe a protocol to prepare single-cell suspension from mouse testes. Overall, the procedure requires a short time to complete (4-5 hours depending on the number of needed cells), which facilitates many downstream applications.

Functionally non-redundant paralogs spe-47 and spe-50 encode FB-MO associated proteins and interact with him-8

The activation of C. elegans spermatids to crawling spermatozoa is affected by a number of genes including spe-47. Here, we investigate a paralog to spe-47: spe-50, which has a highly conserved sequence and expression, but which is not functionally redundant to spe-47. Phylogenetic analysis indicates that the duplication event that produced the paralogs occurred prior to the radiation of the Caenorhabditis species included in the analysis, allowing a long period for the paralogs to diverge in function. Furthermore, we observed that knockout mutations in both genes, either alone or together, have little effect on sperm function. However, hermaphrodites harboring both knockout mutations combined with a third mutation in the him-8 gene are nearly self-sterile due to a sperm defect, even though they have numerous apparently normal sperm within their spermathecae. We suggest that the sperm in these triple mutants are defective in fusing with oocytes, and that the effect of the him-8 mutation is unclear but likely due to its direct or indirect effect on local chromatin structure and function.

The conserved molting/circadian rhythm regulator NHR-23/NR1F1 serves as an essential co-regulator of C. elegans spermatogenesis

In sexually reproducing metazoans, spermatogenesis is the process by which uncommitted germ cells give rise to haploid sperm. Work in model systems has revealed mechanisms controlling commitment to the sperm fate, but how this fate is subsequently executed remains less clear. While studying the well-established role of the conserved nuclear hormone receptor transcription factor, NHR-23/NR1F1, in regulating C. elegans molting, we discovered that NHR-23/NR1F1 is also constitutively expressed in developing primary spermatocytes and is a critical regulator of spermatogenesis. In this novel role, NHR-23/NR1F1 functions downstream of the canonical sex-determination pathway. Degron-mediated depletion of NHR-23/NR1F1 within hermaphrodite or male germlines causes sterility due to an absence of functional sperm, as depleted animals produce arrested primary spermatocytes rather than haploid sperm. These spermatocytes arrest in prometaphase I and fail to either progress to anaphase or attempt spermatid-residual body partitioning. They make sperm-specific membranous organelles but fail to assemble their major sperm protein into fibrous bodies. NHR-23/NR1F1 appears to function independently of the known SPE-44 gene regulatory network, revealing the existence of an NHR-23/NR1F1-mediated module that regulates the spermatogenesis program.

DICER regulates the expression of major satellite repeat transcripts and meiotic chromosome segregation during spermatogenesis

Constitutive heterochromatin at the pericentric regions of chromosomes undergoes dynamic changes in its epigenetic and spatial organization during spermatogenesis. Accurate control of pericentric heterochromatin is required for meiotic cell divisions and production of fertile and epigenetically intact spermatozoa. In this study, we demonstrate that pericentric heterochromatin is expressed during mouse spermatogenesis to produce major satellite repeat (MSR) transcripts. We show that the endonuclease DICER localizes to the pericentric heterochromatin in the testis. Furthermore, DICER forms complexes with MSR transcripts, and their processing into small RNAs is compromised in Dicer1 knockout mice leading to an elevated level of MSR transcripts in meiotic cells. We also show that defective MSR forward transcript processing in Dicer1 cKO germ cells is accompanied with reduced recruitment of SUV39H2 and H3K9me3 to the pericentric heterochromatin and meiotic chromosome missegregation. Altogether, our results indicate that the physiological role of DICER in maintenance of male fertility extends to the regulation of pericentric heterochromatin through direct targeting of MSR transcripts.

Role of GPER-Mediated Signaling in Testicular Functions and Tumorigenesis

Estrogen signaling plays important roles in testicular functions and tumorigenesis. Fifteen years ago, it was discovered that a member of the G protein-coupled receptor family, GPR30, which binds also with high affinity to estradiol and is responsible, in part, for the rapid non-genomic actions of estrogens. GPR30, renamed as GPER, was detected in several tissues including germ cells (spermatogonia, spermatocytes, spermatids) and somatic cells (Sertoli and Leydig cells). In our previous review published in 2014, we summarized studies that evidenced a role of GPER signaling in mediating estrogen action during spermatogenesis and testis development. In addition, we evidenced that GPER seems to be involved in modulating estrogen-dependent testicular cancer cell growth; however, the effects on cell survival and proliferation depend on specific cell type. In this review, we update the knowledge obtained in the last years on GPER roles in regulating physiological functions of testicular cells and its involvement in neoplastic transformation of both germ and somatic cells. In particular, we will focus our attention on crosstalk among GPER signaling, classical estrogen receptors and other nuclear receptors involved in testis physiology regulation.

Developmental origins of transgenerational sperm histone retention following ancestral exposures

Numerous environmental toxicants have been shown to induce the epigenetic transgenerational inheritance of disease and phenotypic variation. Alterations in the germline epigenome are necessary to transmit transgenerational phenotypes. In previous studies, the pesticide DDT (dichlorodiphenyltrichloroethane) and the agricultural fungicide vinclozolin were shown to promote the transgenerational inheritance of sperm differential DNA methylation regions, non-coding RNAs and histone retention, which are termed epimutations. These epimutations are able to mediate this epigenetic inheritance of disease and phenotypic variation. The current study was designed to investigate the developmental origins of the transgenerational differential histone retention sites (called DHRs) during gametogenesis of the sperm. Vinclozolin and DDT were independently used to promote the epigenetic transgenerational inheritance of these DHRs. Male control lineage, DDT lineage and vinclozolin lineage F3 generation rats were used to isolate round spermatids, caput epididymal spermatozoa, and caudal sperm. The DHRs distinguishing the control versus DDT lineage or vinclozolin lineage samples were determined at these three developmental stages. DHRs and a reproducible core of histone H3 retention sites were observed using an H3 chromatin immunoprecipitation-sequencing (ChIP-Seq) analysis in each of the germ cell populations. The chromosomal locations and genomic features of the DHRs were analyzed. A cascade of epigenetic histone retention site alterations was found to be initiated in the round spermatids and then further modified during epididymal sperm maturation. Observations show that in addition to alterations in sperm DNA methylation and ncRNA expression previously identified, the induction of differential histone retention sites (DHRs) in the later stages of spermatogenesis also occurs. This novel component of epigenetic programming during spermatogenesis can be environmentally altered and transmitted to subsequent generations through epigenetic transgenerational inheritance.

HIPK4 is essential for murine spermiogenesis

Mammalian spermiogenesis is a remarkable cellular transformation, during which round spermatids elongate into chromatin-condensed spermatozoa. The signaling pathways that coordinate this process are not well understood, and we demonstrate here that homeodomain-interacting protein kinase 4 (HIPK4) is essential for spermiogenesis and male fertility in mice. HIPK4 is predominantly expressed in round and early elongating spermatids, and Hipk4 knockout males are sterile, exhibiting phenotypes consistent with oligoasthenoteratozoospermia. Hipk4 mutant sperm have reduced oocyte binding and are incompetent for in vitro fertilization, but they can still produce viable offspring via intracytoplasmic sperm injection. Optical and electron microscopy of HIPK4-null male germ cells reveals defects in the filamentous actin (F-actin)-scaffolded acroplaxome during spermatid elongation and abnormal head morphologies in mature spermatozoa. We further observe that HIPK4 overexpression induces branched F-actin structures in cultured fibroblasts and that HIPK4 deficiency alters the subcellular distribution of an F-actin capping protein in the testis, supporting a role for this kinase in cytoskeleton remodeling. Our findings establish HIPK4 as an essential regulator of sperm head shaping and potential target for male contraception.

Revealing stage-specific expression patterns of long noncoding RNAs along mouse spermatogenesis

The discovery of a large number of long noncoding RNAs (lncRNAs), and the finding that they may play key roles in different biological processes, have started to provide a new perspective in the understanding of gene regulation. It has been shown that the testes express the highest amount of lncRNAs among different vertebrate tissues. However, although some studies have addressed the characterization of lncRNAs along spermatogenesis, an exhaustive analysis of the differential expression of lncRNAs at its different stages is still lacking. Here, we present the results for lncRNA transcriptome profiling along mouse spermatogenesis, employing highly pure flow sorted spermatogenic stage-specific cell populations, strand-specific RNAseq, and a combination of up-to-date bioinformatic pipelines for analysis. We found that the vast majority of testicular lncRNA genes are expressed at post-meiotic stages (i.e. spermiogenesis), which are characterized by extensive post-transcriptional regulation. LncRNAs at different spermatogenic stages shared common traits in terms of transcript length, exon number, and biotypes. Most lncRNAs were lincRNAs, followed by a high representation of antisense (AS) lncRNAs. Co-expression analyses showed a high correlation along the different spermatogenic stage transitions between the expression patterns of AS lncRNAs and their overlapping protein-coding genes, raising possible clues about lncRNA-related regulatory mechanisms. Interestingly, we observed the co-localization of an AS lncRNA and its host sense mRNA in the chromatoid body, a round spermatids-specific organelle that has been proposed as a reservoir of RNA-related regulatory machinery. An additional, intriguing observation is the almost complete lack of detectable expression for Y-linked testicular lncRNAs, despite that a high number of lncRNA genes are annotated for this chromosome.

[Expression of Dnajb13 and its involvement in the apoptosis of spermatogenic cells in the testis of the mouse with cryptorchidism]

OBJECTIVE

To study the mRNA and protein expressions of Dnajb13 and its localization in the testis of the mouse with cryptorchidism and its association with the apoptosis of spermatogenic cells.

METHODS

The localization of Dnajb13 in the spermatogenic cells of 8-week-old mice was detected by immunohistochemistry. The model of unilateral cryptorchidism was surgically established in the mice and verified by TUNEL, flow cytometry and morphological observation. The apoptosis of the spermatogenic cells was analyzed and the mRNA and protein expressions of Dnajb13 in both cryptorchid and healthy testes were determined by quantitative polymerase chain reaction (qPCR), Western blot and immunohistochemistry at 1, 2, 3, 4, 5, 6, 9 and 15 days after modeling.

RESULTS

Immunohistochemistry showed that Dnajb13 was localized in the elongated spermatids at steps 9－16 of spermiogenesis in the testis tissue of the healthy mice. TUNEL and flow cytometry manifested that the round spermatids at step 1 and primary spermatocytes in miosis were most sensitive to elevated temperature. After modeling, apoptosis was first observed in the round spermatids at steps 1－8, which were decreased from 17.09% to 6.52% (P < 0.05), then in the spermatids during metamorphosis at steps 9－16, and then in the primary spermatocytes. At 3 days after surgery, the expression of Dnajb13 mRNA in the cryptorchid testis was 1.6 times higher than that in the healthy one (P < 0.05) and decreased at 4 days, 1.2 times that of the normal. The expression of the Dnajb13 protein exhibited no significant change at 1－3 days, but a 0.68-fold reduction at 4 days (P < 0.05) and a 0.4-fold reduction at 9 days. Immunohistochemical staining revealed the expression of the Dnajb13 protein in the apoptotic multinucleated giant cells at 6 days.

CONCLUSIONS

Dnajb13 is localized in the spermatids during metamorphosis and in the tails of mature sperm in adult mice, involved in sperm metamorphosis and sperm flagellum formation, and expressed in apoptotic multinucleated giant cells in the cryptorchid testis, which may be associated with the apoptosis of round spermatids at stages Ⅵ－Ⅷ.

Tubulin-binding cofactor E-like (TBCEL), the protein product of the mulet gene, is required in the germline for the regulation of inter-flagellar microtubule dynamics during spermatid individualization

Individual sperm cells are resolved from a syncytium during late step of spermiogenesis known as individualization, which is accomplished by an Individualization Complex (IC) composed of 64 investment cones. mulet encodes Tubulin-binding cofactor E-like (TBCEL), suggesting a role for microtubule dynamics in individualization. Indeed, a population of ∼100 cytoplasmic microtubules fails to disappear in mulet mutant testes during spermatogenesis. This persistence, detected using epi-fluorescence and electron microscopy, suggests that removal of these microtubules by TBCEL is a prerequisite for individualization. Immunofluorescence reveals TBCEL expression in elongated spermatid cysts. In addition, testes from mulet mutant males were rescued to wild type using tubulin-Gal4 to drive TBCEL expression, indicating that the mutant phenotype is caused by the lack of TBCEL. Finally, RNAi driven by bam-GAL4 successfully phenocopied mulet, confirming that mulet is required in the germline for individualization. We propose a model in which the cytoplasmic microtubules serve as alternate tracks for investment cones in mulet mutant testes.This article has an associated First Person interview with the first author of the paper.

Nuclear Export of Cyclin B Mediated by the Nup62 Complex Is Required for Meiotic Initiation in Drosophila Males

BACKGROUND

The central channel of the nuclear pore complex plays an important role in the selective transport of proteins between the nucleus and cytoplasm. Previous studies have demonstrated that the depletion of the Nup62 complex, constructing the nuclear pore channel in premeiotic Drosophila cells, resulted in the absence of meiotic cells. We attempted to understand the mechanism underlying the cell cycle arrest before meiosis.

METHODS

We induced dsRNAs against the nucleoporin mRNAs using the Gal4/UAS system in Drosophila.

RESULTS

The cell cycle of the Nup62-depleted cells was arrested before meiosis without CDK1 activation. The ectopic over-expression of CycB, but not constitutively active CDK1, resulted in partial rescue from the arrest. CycB continued to exist in the nuclei of Nup62-depleted cells and cells depleted of exportin encoded by emb. Protein complexes containing CycB, Emb, and Nup62 were observed in premeiotic spermatocytes. CycB, which had temporally entered the nucleus, was associated with Emb, and the complex was transported back to the cytoplasm through the central channel, interacting with the Nup62 complex. Conclusion: We proposed that CycB is exported with Emb through the channel interacting with the Nup62 complex before the onset of meiosis. The nuclear export ensures the modification and formation of sufficient CycB-CDK1 in the cytoplasm.

Ovol2, a zinc finger transcription factor, is dispensable for spermatogenesis in mice

Ovol2, a mouse homolog of Drosophila ovo, was identified as a zinc finger transcription factor predominantly expressed in testis. However, the function of Ovol2 in postnatal male germ cell development remains enigmatic. Here, we firstly examined the mRNA and protein levels of Ovol2 in developing mouse testes by RT-qPCR and western blot and found that both mRNA and protein of Ovol2 are continually expressed in postnatal developing testes from postnatal day 0 (P0) testes to adult testes (P56) and exhibits its higher level at adult testis. Further testicular immuno-staining revealed that OVOL2 is highly expressed in the spermatogonia, spermatocytes and round spermatids. Interestingly, our conditional ovol2 knockout mouse model show that loss of ovol2 in embryonic germ cells does not affect fecundity in mice. Our data also show that Ovol1 may have compensated for the loss of Ovol2 functions in germ cells. Overall, our data indicate that ovol2 is dispensable for germ cell development and spermatogenesis.

The effects of hexaconazole and epoxiconazole enantiomers on metabolic profile following exposure to zebrafish (Danio rerio) as well as the histopathological changes

Hexaconazole and epoxiconazole are the worldwidely used fungicides. However, limited information is known about the toxicological effects of their enantiomers on aquatic organisms. In this study, zebrafish were separately exposed to 100 and 1000 μgL^-1 hexaconazole and epoxiconazole enantiomers for 21 d ¹H NMR-based metabolomics analysis showed that the exposure of low and high dose of hexaconazole enantiomers altered energy metabolism, lipid metabolism and amino acid metabolism of zebrafish, with the different metabolic profiles resulted from the same dose of (+)-hexaconazole and (-)-hexaconazole. Similar to hexaconazole enantiomers, the metabolic profiles, including the changes related to energy metabolism, lipid metabolism and amino acid metabolism, were demonstrated in low and high dose epoxiconazole enantiomers treatment groups. There are differences in the metabolic profiles of zebrafish between exposed to (+)-epoxiconazole and (-)-epoxiconazole of the same dose. The results of histological examination revealed that the exposure of both enantiomers for hexaconazole and epoxiconazole resulted in the similar histopathological changes. The exposure of hexaconazole and epoxiconazole enantiomers at low and high dose resulted the vacuolization and swell in the liver of the female and male zebrafish. Compared to female zebrafish, more liver damage was found in male zebrafish in the hexaconazole enantiomers exposure groups. The reduction of spermatids was observed in hexaconazole and epoxiconazole enantiomers treatment groups of both doses. Hexaconazole enantiomers exposure of low and high dose resulted the increase in the number of mature eggs, while such effect was not observed in epoxiconazole enantiomers exposure groups. Hexaconazole and epoxiconazole enantiomers exposure resulted in no changes in brains of female and male zebrafish. As a result, both triazole-based chiral bactericides, hexaconazole and epoxiconazole, have similar toxicological effects but their mechanisms of action are not exactly the same. The above results will play an important part in making the differences in toxic effects of hexaconazole and epoxiconazole enantiomers clear. What's more, it is an indispensable part for an integrated environmental risk assessment.

Integrative Proteomic and Phosphoproteomic Profiling of Testis from Wip1 Phosphatase-Knockout Mice: Insights into Mechanisms of Reduced Fertility

Mice lacking wild-type p53-induced phosphatase 1 (Wip1) display male reproductive defects including smaller testes, subfertility and spermatogenesis defects at the round- and elongating-spermatid stages. However, the molecular mechanisms underlying these abnormalities remain unclear. Here we examined the proteome and phosphoproteome of testes from Wip1-knockout mice using a quantitative proteomic approach. From a total of 6872 proteins and 4280 phosphorylation sites identified, 58 proteins and 159 phosphorylation sites were found to be differentially regulated compared with wild type mice. Pathway enrichment analyses revealed that these regulated proteins and phosphosites were mainly involved in adherens/tight junctions, apoptosis, inflammatory response, spermatogenesis, sperm motility, and cytoskeletal assembly and depolymerization. Wip1-knockout mice showed decreased expression of junction-associated proteins (occludin, ZO-1, and N-cadherin) and impaired integrity of the blood-testis barrier. In addition, Wip1 deficiency was associated with elevated levels of cytokines and germ cell apoptosis in the testis. These results suggest that proinflammatory cytokines may impair the blood-testis barrier dynamics by decreasing the expression of junction-associated proteins, which could lead to subfertility and spermatogenesis defects. Collectively, these findings help to explain the low reproductive function caused by Wip1 deletion and provide novel insights into our understanding of causes of male infertility.

Germ cell arrest associated with aSETX mutation in ataxia oculomotor apraxia type 2

Ataxia with oculomotor apraxia type 2 (AOA2) is a rare autosomal recessive neurodegenerative disorder characterized by cerebellar atrophy, peripheral neuropathy and oculomotor apraxia. It is caused by mutations in the SETX gene that encodes senataxin, a ubiquitously expressed protein that mediates processes, including transcription, transcription termination, DNA repair, RNA processing, DNA-RNA hybrid (R-loop) elimination and telomere stability. In mice, senataxin is essential for male germ cell development and fertility through its role in meiotic recombination and sex chromosome inactivation. AOA2 is associated with hypogonadism in women, but there are no reports of hypogonadism or infertility in men. We describe the first case of human male infertility caused by germ cell arrest in a man with AOA2. Our patient has a homozygous mutation in the SETX gene (NC_000009.11:g.135158775dup), which results in a frameshift and premature protein termination (NM_015046.6:c.6422dup, p.[Ser2142Glufs*23]). In accordance with the murine phenotype, testis histology revealed disrupted seminiferous tubules with spermatogonia and primary spermatocytes, but absent spermatids. Collectively, these data support an essential role of senataxin in human spermatogenesis, and provide a compelling case that men with AOA2 should be counselled at diagnosis about the possibility of infertility.

Src family kinases (SFKs) and cell polarity in the testis

Non-receptor Src family kinases (SFKs), most notably c-Src and c-Yes, are recently shown to be expressed by Sertoli and/or germ cells in adult rat testes. Studies have shown that SFKs are involved in modulating the cell cytoskeletal function, and involved in endocytic vesicle-mediated protein endocytosis, transcytosis and/or recycling as well as intracellular protein degradation events. Furthermore, a knockdown to SFKs, in particular c-Yes, has shown to induce defects in spermatid polarity. These findings, coupled with emerging evidence in the field, thus prompt us to critically evaluate them to put forth a developing concept regarding the role of SFKs and cell polarity, which will become a basis to design experiments for future investigations.

Cell polarity and cytoskeletons-Lesson from the testis

Cell polarity in the adult mammalian testis refers to the polarized alignment of developing spermatids during spermiogenesis and the polarized organization of organelles (e.g., phagosomes, endocytic vesicles, Sertoli cell nuclei, Golgi apparatus) in Sertoli cells and germ cells to support spermatogenesis. Without these distinctive features of cell polarity in the seminiferous epithelium, it is not possible to support the daily production of millions of sperm in the limited space provided by the seminiferous tubules in either rodent or human males through the adulthood. In short, cell polarity provides a novel mean to align spermatids and the supporting organelles (e.g., phagosomes, Golgi apparatus, endocytic vesicles) in a highly organized fashion spatially in the seminiferous epithelium during the epithelial cycle of spermatogenesis. This is analogous to different assembling units in a manufacturing plant such that as developing spermatids move along the "assembly line" conferred by Sertoli cells, different structural/functional components can be added to (or removed from) the developing spermatids during spermiogenesis, so that functional spermatozoa are produced at the end of the assembly line. Herein, we briefly review findings regarding the regulation of cell polarity in the testis with specific emphasis on developing spermatids, supported by an intriguing network of regulatory proteins along a local functional axis. Emerging evidence has suggested that cell cytoskeletons provide the tracks which in turn confer the unique assembly lines in the seminiferous epithelium. We also provide some thought-provoking concepts based on which functional experiments can be designed in future studies.

Actin nucleator Spire 1 is a regulator of ectoplasmic specialization in the testis

Germ cell differentiation during the epithelial cycle of spermatogenesis is accompanied by extensive remodeling at the Sertoli cell-cell and Sertoli cell-spermatid interface to accommodate the transport of preleptotene spermatocytes and developing spermatids across the blood-testis barrier (BTB) and the adluminal compartment of the seminiferous epithelium, respectively. The unique cell junction in the testis is the actin-rich ectoplasmic specialization (ES) designated basal ES at the Sertoli cell-cell interface, and the apical ES at the Sertoli-spermatid interface. Since ES dynamics (i.e., disassembly, reassembly and stabilization) are supported by actin microfilaments, which rapidly converts between their bundled and unbundled/branched configuration to confer plasticity to the ES, it is logical to speculate that actin nucleation proteins play a crucial role to ES dynamics. Herein, we reported findings that Spire 1, an actin nucleator known to polymerize actins into long stretches of linear microfilaments in cells, is an important regulator of ES dynamics. Its knockdown by RNAi in Sertoli cells cultured in vitro was found to impede the Sertoli cell tight junction (TJ)-permeability barrier through changes in the organization of F-actin across Sertoli cell cytosol. Unexpectedly, Spire 1 knockdown also perturbed microtubule (MT) organization in Sertoli cells cultured in vitro. Biochemical studies using cultured Sertoli cells and specific F-actin vs. MT polymerization assays supported the notion that a transient loss of Spire 1 by RNAi disrupted Sertoli cell actin and MT polymerization and bundling activities. These findings in vitro were reproduced in studies in vivo by RNAi using Spire 1-specific siRNA duplexes to transfect testes with Polyplus in vivo-jetPEI as a transfection medium with high transfection efficiency. Spire 1 knockdown in the testis led to gross disruption of F-actin and MT organization across the seminiferous epithelium, thereby impeding the transport of spermatids and phagosomes across the epithelium and perturbing spermatogenesis. In summary, Spire 1 is an ES regulator to support germ cell development during spermatogenesis.

Comparative expression profiling of testis-enriched genes regulated during the development of spermatogonial cells

The testis has been identified as the organ in which a large number of tissue-enriched genes are present. However, a large portion of transcripts related to each stage or cell type in the testis still remains unknown. In this study, databases combined with confirmatory measurements were used to investigate testis-enriched genes, localization in the testis, developmental regulation, gene expression profiles of testicular disease, and signaling pathways. Our comparative analysis of GEO DataSets showed that 24 genes are predominantly expressed in testis. Cellular locations of 15 testis-enriched proteins in human testis have been identified and most of them were located in spermatocytes and round spermatids. Real-time PCR revealed that expressions of these 15 genes are significantly increased during testis development. Also, an analysis of GEO DataSets indicated that expressions of these 15 genes were significantly decreased in teratozoospermic patients and polyubiquitin knockout mice, suggesting their involvement in normal testis development. Pathway analysis revealed that most of those 15 genes are implicated in various sperm-related cell processes and disease conditions. This approach provides effective strategies for discovering novel testis-enriched genes and their expression patterns, paving the way for future characterization of their functions regarding infertility and providing new biomarkers for specific stages of spematogenesis.

Arachidonic acid triggers [Ca2+]i increases in rat round spermatids by a likely GPR activation, ERK signalling and ER/acidic compartments Ca2+ release

Arachidonic acid (AA), a compound secreted by Sertoli cells (SC) in a FSH-dependent manner, is able to induce the release of Ca²⁺ from internal stores in round spermatids and pachytene spermatocytes. In this study, the possible site(s) of action of AA in round spermatids, the signalling pathways associated and the intracellular Ca²⁺ stores targeted by AA-induced signalling were pharmacologically characterized by measuring intracellular Ca²⁺ using fluorescent Ca²⁺ probes. Our results suggest that AA acts by interacting with a fatty acid G protein coupled receptor, initiating a G protein signalling cascade that may involve PLA2 and ERK activation, which in turn opens intracellular ryanodine-sensitive channels as well as NAADP-sensitive channels in acidic intracellular Ca²⁺ stores. The results presented here also suggest that AMPK and PKA modulate this AA-induced Ca²⁺ release from intracellular Ca²⁺ stores in round spermatids. We propose that unsaturated free fatty acid lipid signalling in the seminiferous tubule is a novel regulatory component of rat spermatogenesis.

Purification and Analysis of Male Germ Cells from Adult Mouse Testis

Isolation of pools of spermatogenic cells at specific developmental stages is essential for the investigations of molecular events controlling critical transitions during spermatogenesis. Large-scale cell purification techniques allow for combined proteomics, genomics, and transcriptomics studies. Herein, we describe a procedure for the purification of meiotic and post-meiotic male germ cells from adult mouse testes. We also describe how the fractionated cell populations could be used for further studies. In our laboratory, these protocols are routinely used to specifically investigate the molecular basis of histone acetylation/acylation-driven epigenetic programming.

Testis-Specific Bb8 Is Essential in the Development of Spermatid Mitochondria

Mitochondria are essential organelles of developing spermatids in Drosophila, which undergo dramatic changes in size and shape after meiotic division, where mitochondria localized in the cytoplasm, migrate near the nucleus, aggregate, fuse and create the Nebenkern. During spermatid elongation the two similar mitochondrial derivatives of the Nebenkern start to elongate parallel to the axoneme. One of the elongated mitochondrial derivatives starts to lose volume and becomes the minor mitochondrial derivative, while the other one accumulates paracrystalline and becomes the major mitochondrial derivative. Proteins and intracellular environment that are responsible for cyst elongation and paracrystalline formation in the major mitochondrial derivative need to be identified. In this work we investigate the function of the testis specific big bubble 8 (bb8) gene during spermatogenesis. We show that a Minos element insertion in bb8 gene, a predicted glutamate dehydrogenase, causes recessive male sterility. We demonstrate bb8 mRNA enrichment in spermatids and the mitochondrial localisation of Bb8 protein during spermatogenesis. We report that megamitochondria develop in the homozygous mutant testes, in elongating spermatids. Ultrastructural analysis of the cross section of elongated spermatids shows enlarged mitochondria and the production of paracrystalline in both major and minor mitochondrial derivatives. Our results suggest that the Bb8 protein and presumably glutamate metabolism has a crucial role in the normal development and establishment of the identity of the mitochondrial derivatives during spermatid elongation.

Differential roles of estrogen receptors, ESR1 and ESR2, in adult rat spermatogenesis

Estrogens, through their receptors, play an important role in regulation of spermatogenesis. However, the precise role of the estrogen receptors (ESR1 and ESR2) has been difficult to determine as in vivo estradiol treatment would signal through both the ESRs. Hence we had developed in vivo selective ESR agonist administration models in adult male rats to decipher the individual roles of the ESRs. Treatment with both ESR1 and ESR2 agonists decreased sperm counts after 60 days of treatment. The present study aimed to delineate the precise causes of decreased sperm counts following treatment with the two ESR agonists. Treatment with ESR1 agonist causes an arrest in differentiation of round spermatids into elongated spermatids, mainly due to down-regulation of genes involved in spermiogenesis. ESR2 agonist administration reduces sperm counts due to spermiation failure and spermatocyte apoptosis. Spermiation failure observed is due to defects in tubulobulbar complex formation because of decrease in expression of genes involved in actin remodelling. The increase in spermatocyte apoptosis could be due to increase in oxidative stress and decrease in transcripts of anti-apoptotic genes. Our results suggest that the two ESRs regulate distinct aspects of spermatogenesis. ESR1 is mainly involved with regulation of spermiogenesis, while ESR2 regulates spermatocyte apoptosis and spermiation. Activation of estrogen signaling through either of the receptors can affect their respective processes during spermatogenesis and lead to low sperm output. Since many environmental estrogens can bind to the two ESRs with different affinities, these observations can be useful in understanding their potential effects on spermatogenesis.

Successful xenogeneic germ cell transplantation from Jundia catfish (Rhamdia quelen) into adult Nile tilapia (Oreochromis niloticus) testes

Fish germ cell transplantation presents several important potential applications for aquaculture, including the preservation of germplasm from endangered fish species with high genetic and commercial values. Using this technique in studies developed in our laboratory with adult male Nile tilapias (Oreochromis niloticus), all the necessary procedures were successfully established, allowing the production of functional sperm and healthy progeny approximately 2months after allogeneic transplantation. In the present study, we evaluated the viability of the adult Nile tilapia testis to generate sperm after xenogeneic transplant of germ cells from sexually mature Jundia catfish (Rhamdia quelen) that belong to a different taxonomic order. Therefore, in order to investigate at different time-periods post-transplantation, the presence and development of donor PKH26 labeled catfish germ cells were followed in the tilapia seminiferous tubules. From 7 to 20days post-transplantation, only PKH26 labeled spermatogonia were observed, whereas spermatocytes at different stages of development were found at 70days. Germ cell transplantation success and progression of spermatogenesis were indicated by the presence of labeled PKH26 spermatids and sperm on days 90 and 120 post-transplantation, respectively. Confirming the presence of the catfish genetic material in the tilapia testis, all recipient tilapias evaluated (n=8) showed the genetic markers evaluated. Therefore, we demonstrated for the first time that the adult Nile tilapia testis offers the functional conditions for development of spermatogenesis with sperm production from a fish species belonging to a different order, which provides an important new venue for aquaculture advancement.

Planar Cell Polarity (PCP) Protein Vangl2 Regulates Ectoplasmic Specialization Dynamics via Its Effects on Actin Microfilaments in the Testes of Male Rats

Planar cell polarity (PCP) proteins confer polarization of a field of cells (eg, elongating/elongated spermatids) within the plane of an epithelium such as the seminiferous epithelium of the tubule during spermatogenesis. In adult rat testes, Sertoli and germ cells were found to express PCP core proteins (eg, Van Gogh-like 2 [Vangl2]), effectors, ligands, and signaling proteins. Vangl2 expressed predominantly by Sertoli cells was localized at the testis-specific, actin-rich ectoplasmic specialization (ES) at the Sertoli-spermatid interface in the adluminal compartment and also Sertoli-Sertoli interface at the blood-testis barrier (BTB) and structurally interacted with actin, N-cadherin, and another PCP/polarity protein Scribble. Vangl2 knockdown (KD) by RNA interference in Sertoli cells cultured in vitro with an established tight junction-permeability barrier led to BTB tightening, whereas its overexpression using a full-length cDNA construct perturbed the barrier function. These changes were mediated through an alteration on the organization actin microfilaments at the ES in Sertoli cells, involving actin-regulatory proteins, epidermal growth factor receptor pathway substrate 8, actin-related protein 3, and Scribble, which in turn affected the function of adhesion protein complexes at the ES during the epithelial cycle of spermatogenesis. Using Polyplus in vivo-jetPEI reagent as a transfection medium to silence Vangl2 in the testis in vivo by RNA interference with high efficacy, Vangl2 KD led to changes in F-actin organization at the ES in the epithelium, impeding spermatid and phagosome transport and spermatid polarity, meiosis, and BTB dynamics. For instance, step 19 spermatids remained embedded in the epithelium alongside with step 9 and 10 spermatids in stages IX-X tubules. In summary, the PCP protein Vangl2 is an ES regulator through its effects on actin microfilaments in the testis.

Coordination of Actin- and Microtubule-Based Cytoskeletons Supports Transport of Spermatids and Residual Bodies/Phagosomes During Spermatogenesis in the Rat Testis

Germ cell transport across the seminiferous epithelium during spermatogenesis requires the intricate coordination of cell junctions, signaling proteins, and both actin- and microtubule (MT)-based cytoskeletons. Although the involvement of cytoskeletons in germ cell transport has been suggested, the precise mechanism(s) remains elusive. Based on growing evidence that actin and MT interactions underlie fundamental cellular processes, such as cell motility, it is unlikely that actin- and MT-based cytoskeletons work independently to regulate germ cell transport in the testis. Using rats treated with adjudin, a potential male contraceptive that disrupts spermatid adhesion and transport in the testis, as a study model, we show herein that actin- and MT-based cytoskeletons are both necessary for transport of spermatids and residual bodies/phagosomes across the seminiferous epithelium in adult rat testes. Analysis of intratubular expression of F-actin and tubulin revealed disruption of both actin and MT networks, concomitant with misdirected spermatids and phagosomes in rats treated with adjudin. Actin regulatory proteins, epidermal growth factor receptor pathway substrate 8 and actin-related protein 3, were mislocalized and down-regulated at the actin-rich anchoring junction between germ and Sertoli cells (apical ectoplasmic specialization) after adjudin treatment. Nonreceptor tyrosine kinase p-FAK-Tyr(407), known to regulate F-actin nucleation via actin-related protein 3, was also mislocalized and down-regulated at the apical ectoplasmic specialization, corroborating the observation of actin cytoskeleton disruption. Additionally, spatiotemporal expression of MT regulatory protein end-binding protein 1, shown to be involved in MT-actin cross talk herein, was also disrupted after adjudin treatment. In summary, spermatid/phagosome transport across the epithelium during spermatogenesis requires the coordination between actin- and MT-based cytoskeletons.

Complete Meiosis from Embryonic Stem Cell-Derived Germ Cells In Vitro

In vitro generation of functional gametes is a promising approach for treating infertility, although faithful replication of meiosis has proven to be a substantial obstacle to deriving haploid gamete cells in culture. Here we report complete in vitro meiosis from embryonic stem cell (ESC)-derived primordial germ cells (PGCLCs). Co-culture of PGCLCs with neonatal testicular somatic cells and sequential exposure to morphogens and sex hormones reproduced key hallmarks of meiosis, including erasure of genetic imprinting, chromosomal synapsis and recombination, and correct nuclear DNA and chromosomal content in the resulting haploid cells. Intracytoplasmic injection of the resulting spermatid-like cells into oocytes produced viable and fertile offspring, showing that this robust stepwise approach can functionally recapitulate male gametogenesis in vitro. These findings provide a platform for investigating meiotic mechanisms and the potential generation of human haploid spermatids in vitro.

The Src non-receptor tyrosine kinase paradigm: New insights into mammalian Sertoli cell biology

Src kinases are non-receptor tyrosine kinases that phosphorylate diverse substrates, which control processes such as cell proliferation, differentiation and survival; cell adhesion; and cell motility. c-Src, the prototypical member of this protein family, is widely expressed by several organs that include the testis. In the seminiferous epithelium of the adult rat testis, c-Src is highest at the tubule lumen during the release of mature spermatids. Other studies show that testosterone regulates spermatid adhesion to Sertoli cells via c-Src, indicating Src phosphorylates key substrates that prompt the disassembly of Sertoli cell-spermatid junctions. A more recent in vitro study reveals that c-Src participates in the internalization of proteins that constitute the blood-testis barrier, which is present between Sertoli cells, suggesting a similar mechanism of junction disassembly is at play during spermiation. In this review, we discuss recent findings on c-Src, with an emphasis on its role in spermatogenesis in the mammalian testis.

Testis Morphology and Dichotomic Spermatogenesis in the Sugarcane Borer Diatraea saccharalis (F.) (Lepidoptera: Crambidae)

In the present study, we describe the testis morphology and spermatogenesis of the sugarcane borer, one of the most destructive pests of sugarcane, using light, transmission, and scanning electron microscopies. Diatraea saccharalis (F.) larvae have paired, kidney-shaped testes that are limited externally and divided into four follicles by tunica cells. The adults have two fused whitish and spherical testes that are divided into eight follicles and are composed of spermatogonia, spermatocyte, spermatid, and sperm bundles. The spermatogonia and spermatocyte cysts are located at the apical extremity of the follicle, while the spermatid cysts and sperm bundles are located at the basal extremity of the follicle. Inside of the cysts, which are formed by the somatic cells, the germ line cells develop synchronously and are interconnected by cytoplasmic bridges. Each cyst contains only apyrene or eupyrene, and none of the cysts contain both of the cells. The inner part of the apyrene cyst consists of an electron-dense cap as opposed to a nucleus. The eupyrene sperm contains a nucleus, acrosome, and reticular and lacinate appendages. Both of the sperm types have a "9 + 9 + 2" axoneme and two mitochondrial derivatives at the tail region. The spermatogenesis process and spermatozoa morphology are similar to that of other Lepidoptera.

The development of cat testicular sperm cryopreservation protocols: Effects of tissue fragments or sperm cell suspension

In endangered animals that have been found dead or sterilized for medical reasons, testis is the ultimate source of haploid DNA or sperm. Thus, preservation of testicular sperm may be performed to rescue their genetics. The aim of this study was to evaluate protocols for testicular sperm freezing: as tissue fragments or cell suspension in domestic cats as a model. A pair of testes from each cat (n = 9) were cut into eight equal pieces. Four randomly selected pieces were cryopreserved as: (1) tissue pieces using two-step freezing; (2) tissue pieces using a slow passive cooling device (CoolCell); (3) sperm suspension after single-layer centrifugation (SLC) through colloids; and (4) sperm suspension without being processed through SLC. A testicular piece from each cat served as fresh control. Testicular sperm membrane and DNA integrity were evaluated before, and after, the cryopreservation process. In addition, spermatogenic cell types (testicular sperm, spermatogonia, spermatocyte, and spermatid) present in the suspension samples were counted before and after SLC. The results found that testicular sperm membrane integrity in the suspension after SLC process was higher than that in the fragment form neither using the two-step nor CoolCell freezing, both before and after freezing (before freezing: 92.3 ± 3.4 vs. 81 ± 4.5 and 80.0 ± 7.0; after freezing: 84.5 ± 4.6 vs. 71.2 ± 12 and 76.2 ± 4.6; P ≤ 0.05). Testicular sperm DNA integrity was, however, not different among groups. Furthermore, the samples processed through the SLC had higher ration of sperm cells: other spermatogenic cells than those were not processed through the SLC (88.9 ± 3.8 vs. 30 ± 7.9; P ≤ 0.05). In summary, testicular sperm cryopreserved as a minced suspension is considered suitable in terms of preventing sperm membrane integrity, and SLC is considered a selection tool for enriching haploid sperm cells from castrated or postmortem cats.

RFX2 Is a Major Transcriptional Regulator of Spermiogenesis

Spermatogenesis consists broadly of three phases: proliferation of diploid germ cells, meiosis, and finally extensive differentiation of the haploid cells into effective delivery vehicles for the paternal genome. Despite detailed characterization of many haploid developmental steps leading to sperm, only fragmentary information exists on the control of gene expression underlying these processes. Here we report that the RFX2 transcription factor is a master regulator of genes required for the haploid phase. A targeted mutation of Rfx2 was created in mice. Rfx2^-/- mice are perfectly viable but show complete male sterility. Spermatogenesis appears to progress unperturbed through meiosis. However, haploid cells undergo a complete arrest in spermatid development just prior to spermatid elongation. Arrested cells show altered Golgi apparatus organization, leading to a deficit in the generation of a spreading acrosomal cap from proacrosomal vesicles. Arrested cells ultimately merge to form giant multinucleated cells released to the epididymis. Spermatids also completely fail to form the flagellar axoneme. RNA-Seq analysis and ChIP-Seq analysis identified 139 genes directly controlled by RFX2 during spermiogenesis. Gene ontology analysis revealed that genes required for cilium function are specifically enriched in down- and upregulated genes showing that RFX2 allows precise temporal expression of ciliary genes. Several genes required for cell adhesion and cytoskeleton remodeling are also downregulated. Comparison of RFX2-regulated genes with those controlled by other major transcriptional regulators of spermiogenesis showed that each controls independent gene sets. Altogether, these observations show that RFX2 plays a major and specific function in spermiogenesis.

Failure of spermatogenesis, which is presumed to often result from genetic defects, is a common cause of male sterility. Although numerous genes associated with defects in male spermatogenesis have been identified, numerous cases of genetic male infertility remain unelucidated. We report here that the transcription factor RFX2 is a master regulator of gene expression programs required for progression through the haploid phase of spermatogenesis. Male RFX2-deficient mice are completely sterile. Spermatogenesis progresses through meiosis, but haploid cells undergo a complete block in development just prior to spermatid elongation. Gene expression profiling and ChIP-Seq analysis revealed that RFX2 controls key pathways implicated in cilium/flagellum formation, as well as genes implicated in microtubule and vesicle associated transport. The set of genes activated by RFX2 in spermatids exhibits virtually no overlap with those controlled by other known transcriptional regulators of spermiogenesis, establishing RFX2 as an essential new player in this developmental process. RFX2-deficient mice should therefore represent a valuable new model for deciphering the regulatory networks that direct sperm formation, and thereby contribute to the identification of causes of human male infertility.

Disruption of Th2a and Th2b genes causes defects in spermatogenesis

The variant histones TH2A and TH2B are abundant in the testis, but their roles in spermatogenesis remain elusive. Here, we show that male mutant mice lacking both Th2a and Th2b genes were sterile, with few sperm in the epididymis. In the mutant testis, the lack of TH2B was compensated for by overexpression of H2B, whereas overexpression of H2A was not observed, indicating a decrease in the total histone level. Mutant mice exhibited two defects: incomplete release of cohesin at interkinesis after meiosis I and histone replacement during spermiogenesis. In the mutant testis, secondary spermatocytes at interkinesis accumulated and cohesin was not released normally, suggesting that the retained cohesion of sister chromatids delayed the subsequent entry into meiosis II. In addition, impaired chromatin incorporation of TNP2 and degenerated spermatids were observed in the mutant testis. These results suggest that a loss of TH2A and TH2B function in chromatin dynamics or a decrease in the total histone levels causes defects in both cohesin release and histone replacement during spermatogenesis.

Dynamics of Sun5 localization during spermatogenesis in wild type and Dpy19l2 knock-out mice indicates that Sun5 is not involved in acrosome attachment to the nuclear envelope

The acrosome is an organelle that is central to sperm physiology and a defective acrosome biogenesis leads to globozoospermia, a severe male infertility. The identification of the actors involved in acrosome biogenesis is therefore particularly important to decipher the molecular pathogeny of globozoospermia. We recently showed that a defect in the DPY19L2 gene is present in more than 70% of globozoospermic men and demonstrated that Dpy19l2, located in the inner nuclear membrane, is the first protein involved in the attachment of the acrosome to the nuclear envelope (NE). SUN proteins serve to link the nuclear envelope to the cytoskeleton and are therefore good candidates to participate in acrosome-nucleus attachment, potentially by interacting with DPY19L2. In order to characterize new actors of acrosomal attachment, we focused on Sun5 (also called Spag4l), which is highly expressed in male germ cells, and investigated its localization during spermatogenesis. Using immunohistochemistry and Western blot experiments in mice, we showed that Sun5 transits through different cellular compartments during meiosis. In pachytene spermatocytes, it is located in a membranous compartment different to the reticulum. In round spermatids, it progresses to the Golgi and the NE before to be located to the tail/head junction in epididymal sperm. Interestingly, we demonstrate that Sun5 is not, as initially reported, facing the acrosome but is in fact excluded from this zone. Moreover, we show that in Dpy19l2 KO spermatids, upon the detachment of the acrosome, Sun5 relocalizes to the totality of the NE suggesting that the acrosome attachment excludes Sun5 from the NE facing the acrosome. Finally, Western-blot experiments demonstrate that Sun5 is glycosylated. Overall, our work, associated with other publications, strongly suggests that the attachment of the acrosome to the nucleus does not likely depend on the formation of SUN complexes.

Fascin 1 is an actin filament-bundling protein that regulates ectoplasmic specialization dynamics in the rat testis

In the testis, spermatids are polarized cells, with their heads pointing toward the basement membrane during maturation. This polarity is crucial to pack the maximal number of spermatids in the seminiferous epithelium so that millions of sperms can be produced daily. A loss of spermatid polarity is detected after rodents are exposed to toxicants (e.g., cadmium) or nonhormonal male contraceptives (e.g., adjudin), which is associated with a disruption on the expression and/or localization of polarity proteins. In the rat testis, fascin 1, an actin-bundling protein found in mammalian cells, was expressed by Sertoli and germ cells. Fascin 1 was a component of the ectoplasmic specialization (ES), a testis-specific anchoring junction known to confer spermatid adhesion and polarity. Its expression in the seminiferous epithelium was stage specific. Fascin 1 was localized to the basal ES at the Sertoli cell-cell interface of the blood-testis barrier in all stages of the epithelial cycle, except it diminished considerably at late stage VIII. Fascin 1 was highly expressed at the apical ES at stage VII-early stage VIII and restricted to the step 19 spermatids. Its knockdown by RNAi that silenced fascin 1 by ~70% in Sertoli cells cultured in vitro was found to perturb the tight junction-permeability barrier via a disruption of F-actin organization. Knockdown of fascin 1 in vivo by ~60-70% induced defects in spermatid polarity, which was mediated by a mislocalization and/or downregulation of actin-bundling proteins Eps8 and palladin, thereby impeding F-actin organization and disrupting spermatid polarity. In summary, these findings provide insightful information on spermatid polarity regulation.

Spermatid cyst polarization in Drosophila depends upon apkc and the CPEB family translational regulator orb2

Mature Drosophila sperm are highly polarized cells—on one side is a nearly 2 mm long flagellar tail that comprises most of the cell, while on the other is the sperm head, which carries the gamete's genetic information. The polarization of the sperm cells commences after meiosis is complete and the 64-cell spermatid cyst begins the process of differentiation. The spermatid nuclei cluster to one side of the cyst, while the flagellar axonemes grows from the other. The elongating spermatid bundles are also polarized with respect to the main axis of the testis; the sperm heads are always oriented basally, while the growing tails extend apically. This orientation within the testes is important for transferring the mature sperm into the seminal vesicles. We show here that orienting cyst polarization with respect to the main axis of the testis depends upon atypical Protein Kinase C (aPKC), a factor implicated in polarity decisions in many different biological contexts. When apkc activity is compromised in the male germline, the direction of cyst polarization within this organ is randomized. Significantly, the mechanisms used to spatially restrict apkc activity to the apical side of the spermatid cyst are different from the canonical cross-regulatory interactions between this kinase and other cell polarity proteins that normally orchestrate polarization. We show that the asymmetric accumulation of aPKC protein in the cyst depends on an mRNA localization pathway that is regulated by the Drosophila CPEB protein Orb2. orb2 is required to properly localize and activate the translation of apkc mRNAs in polarizing spermatid cysts. We also show that orb2 functions not only in orienting cyst polarization with respect to the apical-basal axis of the testis, but also in the process of polarization itself. One of the orb2 targets in this process is its own mRNA. Moreover, the proper execution of this orb2 autoregulatory pathway depends upon apkc.

After completion of meiosis, the 64 cells in the spermatid cyst begin differentiating into sperm. Sperm are highly polarized cells and a critical step in their differentiation is spermatid cyst polarization. Spermatids are also polarized within the testis, with the heads of the elongating spermatids located basally, while the tails extend apically. We show that aPKC accumulates preferentially on the apical side of the cyst during polarization and is required to correctly orient cyst polarization with respect to the apical-basal axis of the testis. Unexpectedly, aPKC activity is spatially restricted by a mechanism that depends upon the CPEB family translational regulator orb2. orb2 is required to asymmetrically localize and activate the translation of apkc mRNAs during spermatid differentiation. In addition to correctly orienting the direction of cyst polarization, orb2 is required for the process of polarization itself. One of the orb2 regulatory targets in this process is its own mRNA, and this autoregulatory activity depends, in turn, upon apkc.

Characterization of the role of tumor necrosis factor apoptosis inducing ligand (TRAIL) in spermatogenesis through the evaluation of trail gene-deficient mice

TRAIL (TNFSF10/Apo2L) is a member of the tumor necrosis factor (TNF) superfamily of proteins and is expressed in human and rodent testis. Although the functional role of TRAIL in spermatogenesis is not known, TRAIL is recognized to induce apoptosis via binding to its cognate receptors; DR4 (TRAIL-R1/TNFRSF10A) and DR5 (TRAIL-R2/TNFRSF10B). Here, we utilize Trail gene-deficient (Trail-/-) mice to evaluate the role of TRAIL in spermatogenesis by measuring testis weight, germ cell apoptosis, and spermatid head count at postnatal day (PND) 28 (pubertal) and PND 56 (adult). Trail-/- mice have significantly reduced testis to body weight ratios as compared to wild-type C57BL/6J at both ages. Also, Trail-/- mice (PND 28) show a dramatic increase in basal germ cell apoptotic index (AI, 16.77) as compared to C57BL/6J (3.5). In the testis of adult C57BL/6J mice, the AI was lower than in PND 28 C57BL/6J mice (2.2). However, in adult Trail-/- mice, the AI was still higher than that of controls (9.0); indicating a relative high incidence of germ cell apoptosis. Expression of cleaved caspase-8 (CC8) and cleaved caspase-9 (CC9) (markers of the extrinsic and intrinsic apoptotic pathway, respectively) revealed a two-fold increase in the activity of both pathways in adult Trail-/- mice compared to C57BL/6J. Spermatid head counts in adult Trail-/- mice were dramatically reduced by 54% compared to C57BL/6J, indicating these animals suffer a marked decline in the production of mature spermatozoa. Taken together, these findings indicate that TRAIL is an important signaling molecule for maintaining germ cell homeostasis and functional spermatogenesis in the testis.

Sertolin mediates blood-testis barrier restructuring

Two important events that occur during mammalian spermatogenesis are the release of elongated spermatids at late stage VIII of the seminiferous epithelial cycle and the restructuring of the blood-testis barrier (BTB) during stages VIII-XI. Still, it is not completely understood how these cellular events are accomplished within the seminiferous epithelium. In the present study, we investigate how sertolin, a protein that was initially identified, cloned, and partially characterized by our laboratory, functions in these critical events. Sertolin was found at the BTB, as well as at the apical ectoplasmic specialization and apical tubulobulbar complex, where it colocalized with epidermal growth factor receptor kinase substrate 8 and actin-related protein 3, two actin-regulatory proteins. Knockdown of sertolin by RNA interference showed Sertoli cell barrier function to be enhanced when assessed by transepithelial electrical resistance measurements and immunolocalization experiments. By contrast, the integrity of the BTB was disrupted when sertolin was overexpressed in vitro and in vivo. Sertolin overexpression also prompted germ cell loss from the seminiferous epithelium. Taken collectively, these results suggest that sertolin may be involved in coordinating spermatid release and BTB restructuring during spermatogenesis in the rat.

A comprehensive system for generation and evaluation of induced pluripotent stem cells using piggyBac transposition

The most stringent criterion for evaluating pluripotency is generation of chimeric animals with germline transmission ability. Because the quality of induced pluripotent stem cell (iPSC) lines is heterogeneous, an easy and accurate system to evaluate these abilities would be useful. In this study, we describe a simple but comprehensive system for generating and evaluating iPSCs by single transfection of multiple piggyBac (PB) plasmid vectors encoding Tet-inducible polycistronic reprogramming factors, a pluripotent-cell–specific reporter, a constitutively active reporter, and a sperm-specific reporter. Using this system, we reprogrammed 129 and NOD mouse embryonic fibroblasts into iPSCs, and then evaluated the molecular and functional properties of the resultant iPSCs by quantitative RT-PCR analysis and chimera formation assays. The iPSCs contributed extensively to chimeras, as indicated by the constitutively active TagRFP reporter, and also differentiated into sperm, as indicated by the late-spermatogenesis–specific Acr (acrosin)-EGFP reporter. Next, we established secondary MEFs from E13.5 chimeric embryos and efficiently generated secondary iPSCs by simple addition of doxycycline. Finally, we applied this system to establishment and evaluation of rat iPSCs and production of rat sperm in mouse–rat interspecific chimeras. By monitoring the fluorescence of Acr-EGFP reporter, we could easily detect seminiferous tubules containing rat iPSC–derived spermatids and sperm. And, we succeeded to obtain viable offspring by intracytoplasmic sperm injection (ICSI) using these haploid male germ cells. We propose that this system will enable robust strategies for induction and evaluation of iPSCs, not only in rodents but also in other mammals. Such strategies will be especially valuable in non-rodent species, in which verification of germline transmission by mating is inefficient and time-consuming.

Differential permeability of the blood-testis barrier during reinitiation of spermatogenesis in adult male rats

The blood-testis barrier (BTB) sequesters meiotic spermatocytes and differentiating spermatids away from the vascular environment. We aimed to assess whether meiosis and postmeiotic differentiation could occur when the BTB is permeable. Using a model of meiotic suppression and reinitiation, BTB function was assessed using permeability tracers of small, medium, and large (0.6-, 70-, and 150-kDa) sizes to emulate blood- and lymphatic-borne factors that could cross the BTB. Adult rats (n = 9/group) received the GnRH antagonist acyline (10 wk) to suppress gonadotropins, followed by testosterone (24cm Silastic implant), for 2, 4, 7, 10, 15, and 35 days. In acyline-suppressed testes, all tracers permeated the seminiferous epithelium. As spermatocytes up to diplotene stage XIII reappeared, both the 0.6- and 70-kDa tracers, but not 150 kDa, permeated around these cells. Intriguingly, the 0.6- and 70-kDa tracers were excluded from pachytene spermatocytes at stages VII and VIII but not in subsequent stages. The BTB became progressively impermeable to the 0.6- and 70-kDa tracers as stages IV-VII round spermatids reappeared in the epithelium. This coincided with the appearance of the tight junction protein, claudin-12, in Sertoli cells and at the BTB. We conclude that meiosis can occur when the BTB is permeable to factors up to 70 kDa during the reinitiation of spermatogenesis. Moreover, BTB closure corresponds with the presence of particular pachytene spermatocytes and round spermatids. This research has implications for understanding the effects of BTB dynamics in normal spermatogenesis and also potentially in states where spermatogenesis is suppressed, such as male hormonal contraception or infertility.

[Application of chemical activation to in vitro fertilization by round spermatid injection in mice]

OBJECTIVE

To search for an optimal activation protocol by comparing the chemical activation effects of single-activator and combined activation protocols on mouse oocytes following injection of round spermatids (ROSI) from spermatogenic cells cultured in vitro.

METHODS

Using different concentrations of ethanol, ionomycin (Ion), calcium ionophore A23187 (CIA), strontium chloride (SrCl2), cycloheximide (CHX), and 6-dimethylaminopurine (6-DMAP) , we activated post-ROSI oocytes for different times, and activated them by combined protocols at optimal concentrations and action times according to different activation channels. We compared the activation effects of single-activator and combined activation protocols by comparing the rates of fertilization, cleavages, and morulas and blastocysts.

RESULTS

With a single activator, the optimal protocols of different activators were as follows: 7% ethanol for 6 min, 5 micromol/L CIA for 5 min, 5 micromol/L Ion for 5 min, 2 mmol/L 6-DMAP for 2 h, 10 mmol/L SrCl2 for 1.5 h, and 10 microg/ml CHX for 1.5 h, among which 10 mmol/L SrCl2 for 1.5 h achieved the highest rate of morulas and blastocysts, significantly better than CHX (P < 0.05) but with no remarkable difference from other activators. The ethanol + 6-DMAP group showed a significantly higher rate of morulas and blastocysts (29.63%) than all other combined activation groups and single-activator groups except SrCl2 (P < 0.05), and it also exhibited higher rates of normal fertilization, cleavages and morula than the SrCl2 group, but with no significant difference.

CONCLUSION

The single-activator 10 mmol/L SrCl2 for 1.5 h and the combined activation of 7% ethanol for 6 min + 2 mmol/L 6-DMAP for 2 h are the optimal protocols for chemical activation of mouse oocytes following ROSI, and the combined activation of ethanol + 6-DMAP is even superior to the single-activator protocol.