In vitro production of haploid germ cells from fresh or frozen-thawed testicular cells of neonatal bulls

Use of assisted reproductive technologies (ARTs) to shorten the generational interval in ruminants: current status and perspectives

The challenges posed by climate change and increasing world population are stimulating renewed efforts for improving the sustainability of animal production. To meet such challenges, the contribution of genomic selection approaches, in combination with assisted reproductive technologies (ARTs), to spreading and preserving animal genetics is essential. The largest increase in genetic gain can be achieved by shortening the generation interval. This review provides an overview of the current status and progress of advanced ARTs that could be applied to reduce the generation time in both female and male of domestic ruminants. In females, the use of juvenile in vitro embryo transfer (JIVET) enables to generate offspring after the transfer of in vitro produced embryos derived from oocytes of prepubertal genetically superior donors reducing the generational interval and acceleration genetic gain. The current challenge is increasing in vitro embryo production (IVEP) from prepubertal derived oocytes which is still low and variable. The two main factors limiting IVEP success are the intrinsic quality of prepubertal oocytes and the culture systems for in vitro maturation (IVM). In males, advancements in ARTs are providing new strategies to in vitro propagate spermatogonia and differentiate them into mature sperm or even to recapitulate the whole process of spermatogenesis from embryonic stem cells. Moreover, the successful use of immature cells, such as round spermatids, for intracytoplasmic injection (ROSI) and IVEP could allow to complete the entire process in few months. However, these approaches have been successfully applied to human and mouse whereas only a few studies have been published in ruminants and results are still controversial. This is also dependent on the efficiency of ROSI that is limited by the current isolation and selection protocols of round spermatids. In conclusion, the current efforts for improving these reproductive methodologies could lead toward a significant reduction of the generational interval in livestock animals that could have a considerable impact on agriculture sustainability.

In vitro spermatogenesis in artificial testis: current knowledge and clinical implications for male infertility

Men's reproductive health exclusively depends on the appropriate maturation of certain germ cells known as sperm. Certain illnesses, such as Klinefelter syndrome, cryptorchidism, and syndrome of androgen insensitivity or absence of testis maturation in men, resulting in the loss of germ cells and the removal of essential genes on the Y chromosome, can cause non-obstructive azoospermia. According to laboratory research, preserving, proliferating, differentiating, and transplanting spermatogonial stem cells or testicular tissue could be future methods for preserving the fertility of children with cancer and men with azoospermia. Therefore, new advances in stem cell research may lead to promising therapies for treating male infertility. The rate of progression and breakthrough in the area of in vitro spermatogenesis is lower than that of SSC transplantation, but newer methods are also being developed. In this regard, tissue and cell culture, supplements, and 3D scaffolds have opened new horizons in the differentiation of stem cells in vitro, which could improve the outcomes of male infertility. Various 3D methods have been developed to produce cellular aggregates and mimic the organization and function of the testis. The production of an artificial reproductive organ that supports SSCs differentiation will certainly be a main step in male infertility treatment.

Tissue engineering studies in male infertility disorder

Infertility is an important issue among couples worldwide which is caused by a variety of complex diseases. Male infertility is a problem in 7% of all men. In vitro spermatogenesis (IVS) is the experimental approach that has been developed for mimicking seminiferous tubules-like functional structures in vitro. Currently, various researchers are interested in finding and developing a microenvironmental condition or a bioartificial testis applied for fertility restoration via gamete production in vitro. The tissue engineering (TE) has developed new approaches to treat male fertility preservation through development of functional male germ cells. This makes TE a possible future strategy for restoration of male fertility. Although 3D culture systems supply the perception of the effect of cellular interactions in the process of spermatogenesis, formation of a native gradient of autocrine/paracrine factors in 3D culture systems have not been considered. These results collectively suggest that maintaining the microenvironment of testicular cells even in the form of a 3D-culture system is crucial in achieving spermatogenesis ex vivo. It is also possible to engineer the testicular structures using biomaterials to provide a supporting scaffold for somatic and stem cells. The insemination of these cells with GFs is possible for temporally and spatially adjusted release to mimic the microenvironment of the in situ seminiferous epithelium. This review focuses on recent studies and advances in the application of TE strategies to cell-tissue culture on synthetic or natural scaffolds supplemented with growth factors.

Recent advances in endocrine organoids for therapeutic application

The endocrine system, consisting of the hypothalamus, pituitary, endocrine glands, and hormones, plays a critical role in hormone metabolic interactions. The complexity of the endocrine system is a significant obstacle to understanding and treating endocrine disorders. Notably, advances in endocrine organoid generation allow a deeper understanding of the endocrine system by providing better comprehension of molecular mechanisms of pathogenesis. Here, we highlight recent advances in endocrine organoids for a wide range of therapeutic applications, from cell transplantation therapy to drug toxicity screening, combined with development in stem cell differentiation and gene editing technologies. In particular, we provide insights into the transplantation of endocrine organoids to reverse endocrine dysfunctions and progress in developing strategies for better engraftments. We also discuss the gap between preclinical and clinical research. Finally, we provide future perspectives for research on endocrine organoids for the development of more effective treatments for endocrine disorders.

Biomaterials for Testicular Bioengineering: How far have we come and where do we have to go?

Traditional therapeutic interventions aim to restore male fertile potential or preserve sperm viability in severe cases, such as semen cryopreservation, testicular tissue, germ cell transplantation and testicular graft. However, these techniques demonstrate several methodological, clinical, and biological limitations, that impact in their results. In this scenario, reproductive medicine has sought biotechnological alternatives applied for infertility treatment, or to improve gamete preservation and thus increase reproductive rates in vitro and in vivo. One of the main approaches employed is the biomimetic testicular tissue reconstruction, which uses tissue-engineering principles and methodologies. This strategy pursues to mimic the testicular microenvironment, simulating physiological conditions. Such approach allows male gametes maintenance in culture or produce viable grafts that can be transplanted and restore reproductive functions. In this context, the application of several biomaterials have been proposed to be used in artificial biological systems. From synthetic polymers to decellularized matrixes, each biomaterial has advantages and disadvantages regarding its application in cell culture and tissue reconstruction. Therefore, the present review aims to list the progress that has been made and the continued challenges facing testicular regenerative medicine and the preservation of male reproductive capacity, based on the development of tissue bioengineering approaches for testicular tissue microenvironment reconstruction.

Comparison of two methods for prolong storage of decellularized mouse whole testis for tissue engineering application: An experimental study

Background

Biological scaffolds are derived by the decellularization of tissues or organs. Various biological scaffolds, such as scaffolds for the liver, lung, esophagus, dermis, and human testicles, have been produced. Their application in tissue engineering has created the need for cryopreservation processes to store these scaffolds.

Objective

The aim was to compare the two methods for prolong storage testicular scaffolds.

Materials and Methods

In this experimental study, 20 male NMRI mice (8 wk) were sacrificed and their testes were removed and treated with 0.5% sodium dodecyl sulfate followed by Triton X-100 0.5%. The efficiency of decellularization was determined by histology and DNA quantification. Testicular scaffolds were stored in phosphate-buffered saline solution at 4°C or cryopreserved by programmed slow freezing followed by storage in liquid nitrogen. Masson's trichrome staining, Alcian blue staining and immunohistochemistry, collagen assay, and glycosaminoglycan assay were done prior to and after six months of storage under each condition.

Results

Hematoxylin-eosin staining showed no remnant cells after the completion of decellularization. DNA content analysis indicated that approximately 98% of the DNA was removed from the tissue (p = 0.02). Histological evaluation confirmed the preservation of extracellular matrix components in the fresh and frozen-thawed scaffolds. Extracellular matrix components were decreased by 4°C-stored scaffolds. Cytotoxicity tests with mouse embryonic fibroblast showed that the scaffolds were biocompatible and did not have a harmful effect on the proliferation of mouse embryonic fibroblast cells.

Conclusion

Our results demonstrated the superiority of the slow freezing method for prolong storage of testicular scaffolds.

Current progress, challenges, and future prospects of testis organoids†

Spermatogenic failure is believed to be a major cause of male infertility. The establishment of a testis organoid model would facilitate the study of such pathological mechanisms and open the possibility of male fertility preservation. Because of the complex structures and cellular events occurring within the testis, the establishment of a compartmentalized testis organoid with a complete spermatogenic cycle remains a challenge in all species. Since the late 20th century, a great variety of scaffold-based and scaffold-free testis cell culture systems have been established to recapitulate de novo testis organogenesis and in vitro spermatogenesis. The utilization of the hydrogel scaffolds provides a 3D microenvironment for testis cell growth and development, facilitating the reconstruction of de novo testis tissue-like structures and spermatogenic differentiation. Using a combination of different strategies, including the use of various scaffolding biomaterials, the incorporation of the living cells with high self-assembling capacity, and the integration of the advanced fabrication techniques, a scaffold-based testis organoid with a compartmentalized structure that supports in vitro spermatogenesis may be achieved. This article briefly reviews the current progress in the development of scaffold-based testis organoids while focusing on the scaffolding biomaterials (hydrogels), cell sources, and scaffolding approaches. Key challenges in current organoid studies are also discussed along with recommendations for future research.

Advanced bioengineering of male germ stem cells to preserve fertility

In modern life, several factors such as genetics, exposure to toxins, and aging have resulted in significant levels of male infertility, estimated to be approximately 18% worldwide. In response, substantial progress has been made to improve in vitro fertilization treatments (e.g. microsurgical testicular sperm extraction (m-TESE), intra-cytoplasmic sperm injection (ICSI), and round spermatid injection (ROSI)). Mimicking the structure of testicular natural extracellular matrices (ECM) outside of the body is one clear route toward complete in vitro spermatogenesis and male fertility preservation. Here, a new wave of technological innovations is underway applying regenerative medicine strategies to cell-tissue culture on natural or synthetic scaffolds supplemented with bioactive factors. The emergence of advanced bioengineered systems suggests new hope for male fertility preservation through development of functional male germ cells. To date, few studies aimed at in vitro spermatogenesis have resulted in relevant numbers of mature gametes. However, a substantial body of knowledge on conditions that are required to maintain and mature male germ cells in vitro is now in place. This review focuses on advanced bioengineering methods such as microfluidic systems, bio-fabricated scaffolds, and 3D organ culture applied to the germline for fertility preservation through in vitro spermatogenesis.

Stem cell-based therapies for fertility preservation in males: Current status and future prospects

With the decline in male fertility in recent years, strategies for male fertility preservation have received increasing attention. In this study, by reviewing current treatments and recent publications, we describe research progress in and the future directions of stem cell-based therapies for male fertility preservation, focusing on the use of spermatogonial stem cells (SSCs), SSC niches, SSC-based testicular organoids, other stem cell types such as mesenchymal stem cells, and stem cell-derived extracellular vesicles. In conclusion, a more comprehensive understanding of the germ cell microenvironment, stem cell-derived extracellular vesicles, and testicular organoids will play an important role in achieving male fertility preservation.

Effects of Different Biomaterials and Cellular Status on Testicular Cell Self-Organization

A multicellular organism's development is coupled with cellular self-organization, which is regulated by cell-cell interactions and cell-extracellular matrix (ECM) crosstalk. Testicular cells from different species such as mouse, rat, and porcine can self-organize into seminiferous tubules both in vitro and in vivo, but the understanding of the functional role of the ECM during this process is limited. Here, it is shown that mouse testicular cells encapsulated with the biomaterial Matrigel can self-organize into seminiferous tubules with blood-testis barrier (BTB) formation and Leydig cell differentiation. By varying the encapsulation method, a combination of sodium alginate and collagen is used to promote reorganization of seminiferous tubules, which resemble those in vivo. In addition, the self-organization ability of testicular cells declines with advanced cell age, and those germ cells play a pivotal role in this process. These findings will be helpful to understand the self-organization process of testicular cells and provide insights for the reconstruction of testes.

In Vitro Spermatogenesis by Three-dimensional Culture of Spermatogonial Stem Cells on Decellularized Testicular Matrix

Background

In the males, Spermatogonial Stem Cells (SSCs) contribute to the production of sex cells and fertility. In vitro SSCs culture can operate as an effective strategy for studies on spermatogenesis and male infertility treatment. Cell culture in a three-dimensional (3D) substrate, relative to a two-dimensional substrate (2D), creates better conditions for cell interaction and is closer to in vivo conditions. In the present study, in order to create a 3D matrix substrate, decellularized testicular matrix (DTM) was used to engender optimal conditions for SSCs culture and differentiation.

Materials and Methods

After, testicular cells enzymatic extraction from testes of brain-dead donors, the SSCs were proliferated in a specific culture medium for four weeks, and after confirming the identity of the colonies derived from the growth of these cells, they were cultured on a layer of DTM as well as in 2D condition with a differentiated culture medium. In the Sixth week since the initiation of the differentiation culture, the expression of pre meiotic (OCT4 & PLZF ), meiotic (SCP3 & BOULE) and post meiotic (CREM & Protamine-2) genes were measured in both groups.

Results

The results indicated that the expression of pre meiotic, meiotic and post meiotic genes was significantly higher in the cells cultured on DTM (P ≤ 0.001).

Conclusion

SSCs culture in DTM with the creation of ECM and similar conditions with in vivo can be regarded as a way of demonstrating spermatogenesis in vitro, which can be adopted as a treatment modality for male infertility.

Influence of temperature, serum, and gonadotropin supplementation in short- and long-term organotypic culture of human immature testicular tissue

OBJECTIVE

To study how temperature, serum, and gonadotropin supplementation affect the organotypic culture of human immature testicular tissue (ITT) in vitro.

DESIGN

Experimental basic science study.

SETTING

Reproductive biology laboratory.

PATIENT(S)

ITT from 4 boys with cancer that had testicular tissue cryopreserved as part of their fertility preservation treatment.

INTERVENTION(S)

In vitro organotypic culture of ITT, exposed to different temperatures (37°C vs. 34°C), serum (fetal bovine serum [FBS] vs. Knockout Serum Replacement [KOS]), and gonadotropin supplementation (with and without FSH and LH).

MAIN OUTCOME MEASURE(S)

Characterization of the tissue was performed at days 0, 14, and 70 with the use of reverse-transcription quantitative polymerase chain reaction, terminal deoxynucleotide transferase-mediated dUTP nick-end labeling, histologic analysis by means of hematoxylin-eosin staining, and immunohistochemical staining. Hormonal secretion was determined at days 3, 14, 28, and 70 by means of immunofluorescent assay.

RESULT(S)

The 37°C conditions showed an accelerated loss of tubular morphology and higher intratubular apoptosis. KOS supplementation triggered the up-regulation of STAR, SOX9, DAZL, DDX4, PLZF, and UTF1, the percentage of SOX9+/androgen receptor (AR)-positive mature Sertoli cells at day 14, and testosterone secretion. Gonadotropin supplementation increased the numbers of both undifferentiated UTF1+ spermatogonia and premeiotic VASA+/SYCP3+ spermatogonia at day 14, and the number of SOX9+ Sertoli cells at day 70. The low SOX9+/AR+ colocalization, the disorganized pattern of ZO-1, and the progressive decrease of antimüllerian hormone secretion indicated inefficient Sertoli cell maturation in vitro.

CONCLUSION(S)

The 34°C condition in KOS showed the best results for the survival of both spermatogonia and Sertoli cells. FSH/LH supplementation also improved long-term survival of Sertoli cells and the maturation of spermatogonia up to meiotic initiation in short-term culture.

Organ culture of seminiferous tubules using a modified soft agar culture system

BACKGROUND

In-vitro spermatogenesis in mammalian species is considered an important topic in reproductive biology. New strategies for achieving a complete version of spermatogenesis ex vivo have been conducted using an organ culture method or culture of testicular cells in a three-dimensional soft agar culture system (SACS). The aim of this study was to develop a new method that supports spermatogenesis to the meiotic phase and morphologically mature spermatozoa through the culture of testicular cells and seminiferous tubules (STs) in a modified SACS, respectively.

METHODS

First, enzymatically dissociated testicular cells and mechanically dissociated STs of neonatal mice were separately embedded in agarose and then placed on the flat surface of agarose gel half-soaked in the medium to continue culture with a gas-liquid interphase method.

RESULTS

Following 40 days of culture, the meiotic (Scp3) and post-meiotic (Acr) gene expression in aggregates and STs was confirmed by real-time polymerase chain reaction. These results were complemented by immunohistochemistry. The presence of morphologically mature spermatozoa in the frozen sections of STs was demonstrated with hematoxylin and eosin staining. We observed Plzf- or Integrin α6-positive spermatogonia in both cultures after 40 days, indicating the potency of the culture system for both self-renewal and differentiation.

CONCLUSIONS

This technique can be used as a valuable approach for performing research on spermatogenesis and translating it into the human clinical setting.

Differentiation of human male germ cells from Wharton's jelly-derived mesenchymal stem cells

Objective

Recapitulation of the spermatogenesis process in vitro is a tool for studying the biology of germ cells, and may lead to promising therapeutic strategies in the future. In this study, we attempted to transdifferentiate Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) into male germ cells using all-trans retinoic acid and Sertoli cell-conditioned medium.

Methods

Human WJ-MSCs were propagated by the explant culture method, and cells at the second passage were induced with differentiation medium containing all-trans retinoic acid for 2 weeks. Putative germ cells were cultured with Sertoli cell-conditioned medium at 36℃ for 3 more weeks.

Results

The gene expression profile was consistent with the stage-specific development of germ cells. The expression of Oct4 and Plzf (early germ cell markers) was diminished, while Stra8 (a premeiotic marker), Scp3 (a meiotic marker), and Acr and Prm1 (postmeiotic markers) were upregulated during the induction period. In morphological studies, approximately 5% of the cells were secondary spermatocytes that had completed two stages of acrosome formation (the Golgi phase and the cap phase). A few spermatid-like cells that had undergone the initial stage of tail formation were also noted.

Conclusion

Human WJ-MSCs can be transdifferentiated into more advanced stages of germ cells by a simple two-step induction protocol using retinoic acid and Sertoli cell-conditioned medium.

Tissue Engineering to Improve Immature Testicular Tissue and Cell Transplantation Outcomes: One Step Closer to Fertility Restoration for Prepubertal Boys Exposed to Gonadotoxic Treatments

Despite their important contribution to the cure of both oncological and benign diseases, gonadotoxic therapies present the risk of a severe impairment of fertility. Sperm cryopreservation is not an option to preserve prepubertal boys’ reproductive potential, as their seminiferous tubules only contain spermatogonial stem cells (as diploid precursors of spermatozoa). Cryobanking of human immature testicular tissue (ITT) prior to gonadotoxic therapies is an accepted practice. Evaluation of cryopreserved ITT using xenotransplantation in nude mice showed the survival of a limited proportion of spermatogonia and their ability to proliferate and initiate differentiation. However, complete spermatogenesis could not be achieved in the mouse model. Loss of germ cells after ITT grafting points to the need to optimize the transplantation technique. Tissue engineering, a new branch of science that aims at improving cellular environment using scaffolds and molecules administration, might be an approach for further progress. In this review, after summarizing the lessons learned from human prepubertal testicular germ cells or tissue xenotransplantation experiments, we will focus on the benefits that might be gathered using bioengineering techniques to enhance transplantation outcomes by optimizing early tissue graft revascularization, protecting cells from toxic insults linked to ischemic injury and exploring strategies to promote cellular differentiation.

Testicular organoids: a new model to study the testicular microenvironment in vitro?

BACKGROUND

In recent decades, a broad range of strategies have been applied to model the testicular microenvironment in vitro. These models have been utilized to study testicular physiology and development. However, a system that allows investigations into testicular organogenesis and its impact in the spermatogonial stem-cell (SSC) niche in vitro has not been developed yet. Recently, the creation of tissue-specific organ-like structures called organoids has resurged, helping researchers to answer scientific questions that previous in vitro models could not help to elucidate. So far, a small number of publications have concerned the generation of testicular organoids and their application in the field of reproductive medicine and biology.

OBJECTIVE AND RATIONALE

Here, we aim to elucidate whether testicular organoids might be useful in answering current scientific questions about the regulation and function of the SSC niche as well as germ cell proliferation and differentiation, and whether or not the existing in vitro models are already sufficient to address them. Moreover, we would like to discuss how an organoid system can be a better solution to address these prominent scientific problems in our field, by the creation of a rationale parallel to those in other areas where organoid systems have been successfully utilized.

SEARCH METHODS

We comprehensively reviewed publications regarding testicular organoids and the methods that most closely led to the formation of these organ-like structures in vitro by searching for the following terms in both PubMed and the Web of Science database: testicular organoid, seminiferous tubule 3D culture, Sertoli cell 3D culture, testicular cord formation in vitro, testicular morphogenesis in vitro, germ cell 3D culture, in vitro spermatogenesis, testicular de novo morphogenesis, seminiferous tubule de novo morphogenesis, seminiferous tubule-like structures, testicular in vitro model and male germ cell niche in vitro, with no restrictions to any publishing year. The inclusion criteria were based on the relation with the main topic (i.e. testicular organoids, testicular- and seminiferous-like structures as in vitro models), methodology applied (i.e. in vitro culture, culture dimensions (2D, 3D), testicular cell suspension or fragments) and outcome of interest (i.e. organization in vitro). Publications about grafting of testicular tissue, germ-cell transplantation and female germ-cell culture were excluded.

OUTCOMES

The application of organoid systems is making its first steps in the field of reproductive medicine and biology. A restricted number of publications have reported and characterized testicular organoids and even fewer have denominated such structures by this method. However, we detected that a clear improvement in testicular cell reorganization is recognized when 3D culture conditions are utilized instead of 2D conditions. Depending on the scientific question, testicular organoids might offer a more appropriate in vitro model to investigate testicular development and physiology because of the easy manipulation of cell suspensions (inclusion or exclusion of a specific cell population), the fast reorganization of these structures and the controlled in vitro conditions, to the same extent as with other organoid strategies reported in other fields.

WIDER IMPLICATIONS

By way of appropriate research questions, we might use testicular organoids to deepen our basic understanding of testicular development and the SSC niche, leading to new methodologies for male infertility treatment.

Restoring Fertility with Cryopreserved Prepubertal Testicular Tissue: Perspectives with Hydrogel Encapsulation, Nanotechnology, and Bioengineered Scaffolds

New and improved oncological therapies are now able to cure more than 80% of cancer-affected children in Europe. However, such treatments are gonadotoxic and result in fertility issues, especially in boys who are not able to provide a sperm sample before starting chemo/radiotherapy because of their prepubertal state. For these boys, cryopreservation of immature testicular tissue (ITT) is the only available option, aiming to preserve spermatogonial stem cells (SSCs). Both slow-freezing and vitrification have been investigated to this end and are now applied in a clinical setting for SSC cryopreservation. Research now has to focus on methods that will allow fertility restoration. This review discusses different studies that have been conducted on ITT transplantation, including those using growth factor supplementation like free molecules, or tissue encapsulation with or without nanoparticles, as well as the possibility of developing a bioartificial testis that can be used for in vitro gamete production or in vivo transplantation.

Melatonin promotes development of haploid germ cells from early developing spermatogenic cells of Suffolk sheep under in vitro condition

Promotion of spermatogonial stem cell (SSC) differentiation into functional sperms under in vitro conditions is a great challenge for reproductive physiologists. In this study, we observed that melatonin (10(-7) M) supplementation significantly enhanced the cultured SSCs differentiation into haploid germ cells. This was confirmed by the expression of sperm special protein, acrosin. The rate of SSCs differentiation into sperm with melatonin supplementation was 11.85 ± 0.93% which was twofold higher than that in the control. The level of testosterone, the transcriptions of luteinizing hormone receptor (LHR), and the steroidogenic acute regulatory protein (StAR) were upregulated with melatonin treatment. At the early stage of SSCs culture, melatonin suppressed the level of cAMP, while at the later stage, it promoted cAMP production. The similar pattern was observed in testosterone content. Expressions for marker genes of meiosis anaphase, Dnmt3a, and Bcl-2 were upregulated by melatonin. In contrast, Bax expression was downregulated. Importantly, the in vitro-generated sperms were functional and they were capable to fertilize oocytes. These fertilized oocytes have successfully developed to the blastula stage.

Models of in vitro spermatogenesis

Understanding the mechanisms that lead to the differentiation of male germ cells from their spermatogonial stem cells through meiosis to give rise to mature haploid spermatozoa has been a major quest for many decades. Unlike most other cell types this differentiation process is more or less completely dependent upon the cells being located within the strongly structured niche provided by mature Sertoli cells within an intact seminiferous epithelium. While much new information is currently being obtained through the application and description of relevant gene mutations, there is still a considerable need for in vitro models with which to explore the mechanisms involved. Not only are systems of in vitro spermatogenesis important for understanding the basic science, they have marked pragmatic value in offering ex vivo systems for the artificial maturation of immature germ cells from male infertility patients, as well as providing opportunities for the transgenic manipulation of male germ cells. In this review, we have summarized literature relating to simplistic culturing of germ cells, co-cultures of germ cells with other cell types, especially with Sertoli cells, cultures of seminiferous tubule fragments, and briefly mention the opportunities of xenografting larger testicular pieces. The majority of methods are successful in allowing the differentiation of small steps in the progress of spermatogonia to spermatozoa; few tolerate the chromosomal reduction division through meiosis, and even fewer seem able to complete the complex morphogenesis which results in freely swimming spermatozoa. However, recent progress with complex culture environments, such as 3-d matrices, suggest that possibly success is now not too far away.

Fact or fiction: In vitro spermatogenesis

Many previous studies have aimed at spermatogenesis of male murine germ cells in vitro, but no efficient system has been established yet that covers the entire process of mammalian spermatogenesis in a culture dish permanently. In this review, we report on the requirements of spermatogenesis and the current state of different culture methods using testicular tissue fragments, single cell suspensions or three-dimensional culture environments.

Three-step method for proliferation and differentiation of human embryonic stem cell (hESC)-derived male germ cells

The low efficiency of differentiation into male germ cell (GC)-like cells and haploid germ cells from human embryonic stem cells (hESCs) reflects the culture method employed in the two-dimensional (2D)-microenvironment. In this study, we applied a three-step media and calcium alginate-based 3D-culture system for enhancing the differentiation of hESCs into male germ stem cell (GSC)-like cells and haploid germ cells. In the first step, embryoid bodies (EBs) were derived from hESCs cultured in EB medium for 3 days and re-cultured for 4 additional days in EB medium with BMP4 and RA to specify GSC-like cells. In the second step, the resultant cells were cultured in GC-proliferation medium for 7 days. The GSC-like cells were then propagated after selection using GFR-α1 and were further cultured in GC-proliferation medium for 3 weeks. In the final step, a 3D-co-culture system using calcium alginate encapsulation and testicular somatic cells was applied to induce differentiation into haploid germ cells, and a culture containing approximately 3% male haploid germ cells was obtained after 2 weeks of culture. These results demonstrated that this culture system could be used to efficiently induce GSC-like cells in an EB population and to promote the differentiation of ESCs into haploid male germ cells.

Application of testis germ cell transplantation in breeding systems of food producing species: a review

A major benefit of advanced reproduction technologies (ART) in animal breeding is the ability to produce more progeny per individual parent. This is particularly useful with animals of high genetic merit. Testis germ cell transplantation (TGCT) is emerging as a novel reproductive technology with application in animal breeding systems, including the potential for use as an alternative to artificial insemination (AI), an alternative to transgenesis, part of an approach to reducing generation intervals, or an approach toward development of interspecies hybrids. There is one major difference in TGCT between rodents and some other species associated with immunotolerance in heterologous transplantation. In particular, livestock and aquatic species do not require an immunesuppression procedure to allow donor cell survival in recipient testis. Testicular stem cells from a genetically elite individual transplanted into others can develop and produce a surrogate male-an animal that produces the functional sperm of the original individual. Spermatozoa produced from testis stem cells are the only cells in the body of males that can transmit genetic information to the offspring. The isolation and genetic manipulation of testis stem cells prior to transplantation has been shown to create transgenic animals. However, the current success rate of the transplantation procedure in livestock and aquatic species is low, with a corresponding small proportion of donor spermatozoa in the recipient's semen. The propagation of donor cells in culture and preparation of recipient animals are the two main factors that limit the commercial application of this technique. The current paper reviews and compares recent progress and examines the difficulties of TGCT in both livestock and aquatic species, thereby providing new insights into the application of TGCT in food producing animals.

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.

Concise review: Spermatogenesis in an artificial three-dimensional system

Culture of spermatogonial stem cells has been performed under a variety of conditions. Most featured two-dimensional systems, with different types of sera, conditioned media, feeder layers, and growth factors. Some have used three-dimensional (3D) matrices produced from gelatin, collagen, or other material. In spite of their increasingly sophisticated composition, however, complete spermatogenesis in vitro has not yet been achieved. In the seminiferous tubules, spermatogenesis occurs in an environment where cells are embedded in a 3D structure with specific niches regulating each stage of germ cell maturation mediated by hormones and paracrine/autocrine factors. We have recently reported achievement of complete in vitro spermatogenesis of mouse testicular germ cells in a 3D culture system featuring a soft agar matrix. This review discusses the advantages of the 3D culture system for studying the spermatogenic process in its entirety. Also discussed are the steps necessary to expand the applicability of the 3D culture system to human germ cell development and determine the functionality of culture-produced spermatozoa for generating offspring.

Spermatogonial stem cell preservation and transplantation: from research to clinic

STUDY QUESTION

What issues remain to be solved before fertility preservation and transplantation can be offered to prepubertal boys?

SUMMARY ANSWER

The main issues that need further investigation are malignant cell decontamination, improvement of in vivo fertility restoration and in vitro maturation.

WHAT IS KNOWN ALREADY

Prepubertal boys who need gonadotoxic treatment might render sterile for the rest of their life. As these boys do not yet produce sperm cells, they cannot benefit from sperm banking. Spermatogonial stem cell (SSC) banking followed by autologous transplantation has been proposed as a fertility preservation strategy. But before this technique can be applied in the clinic, some important issues have to be resolved.

STUDY DESIGN, SIZE DURATION

Original articles as well as review articles published in English were included in a search of the literature.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Relevant studies were selected by an extensive Medline search. Search terms were fertility preservation, cryopreservation, prepubertal, SSC, testis tissue, transplantation, grafting and in vitro spermatogenesis. The final number of studies selected for this review was 102.

MAIN RESULTS AND THE ROLE OF CHANCE

Cryopreservation protocols for testicular tissue have been developed and are already being used in the clinic. Since the efficiency and safety of SSC transplantation have been reported in mice, transplantation methods are now being adapted to the human testes. Very recently, a few publications reported on in vitro spermatogenesis in mice, but this technique is still far from being applied in a clinical setting.

LIMITATIONS, REASONS FOR CAUTION

Using tissue from cancer patients holds a potential risk for contamination of the collected testicular tissue. Therefore, it is of immense importance to separate malignant cells from the cell suspension before transplantation. Because biopsies obtained from young boys are small and contain only few SSCs, propagation of these cells in vitro will be necessary.

WIDER IMPLICATIONS OF THE FINDINGS

The ultimate use of the banked tissue will depend on the patient's disease. If the patient was suffering from a non-malignant disease, tissue grafting might be offered. In cancer patients, decontaminated cell suspensions will be injected in the testis. For patients with Klinefelter syndrome, the only option would be in vitro spermatogenesis. However, at present, restoring fertility in cancer and Klinefelter patients is not yet possible.

STUDY FUNDING/COMPETING INTEREST(S)

Research Foundation, Flanders (G.0385.08 to H.T.), the Institute for the Agency for Innovation, Belgium (IWT/SB/111245 to E.G.), the Flemish League against Cancer (to E.G.), Kom op tegen kanker (G.0547.11 to H.T.) and the Fund Willy Gepts (to HT). E.G. is a Postdoctoral Fellow of the FWO, Research Foundation, Flanders. There are no conflicts of interest.

Retinol (vitamin A) maintains self-renewal of pluripotent male germline stem cells (mGSCs) from adult mouse testis

Studies have shown that male germline stem cells (mGSCs), which are responsible for maintaining spermatogenesis in the male, could be obtained from mouse and human testis. However, the traditional cultural methods were mostly dependent on serum and feeder, and the initial mGSCs were either obtained from neonatal mice or the detailed description of its potency and origin was not provided. Here we reported a novel (retinol (RE) serum-free and feeder-free) system for the successful culture of adult germline stem cells from adult Kunming mice (8-24 weeks) testis. The isolated mGSCs cultured in RE serum-free and feeder-free medium maintained the typical morphology of undifferentiated embryonic stem cells (ESCs), and they proliferated well in RE medium analyzed by proliferation assay, RT-PCR, microarray, and Western blotting. These cells also showed typical properties of ESCs (alkaline phosphatase (AP) positive, expressions of Oct4, Sox2, Nanog, and SSEA1, with the capacity to form teratomas and differentiate into various types of cells within three germ layers). Taken together, we conclude that RE promotes the self-renewal of mGSCs and maintains the pluripotency of mGSCs, the RE serum-free and feeder-free system may be useful for the culture of pluripotent stem cell lines from adult testis tissues, which provides a new resource for tissue engineering and therapy for infertility.

Long-term proliferation and characterization of human spermatogonial stem cells obtained from obstructive and non-obstructive azoospermia under exogenous feeder-free culture conditions

OBJECTIVES

The aim of the present study was to improve efficiency of isolation and to optimize proliferative potential of human spermatogonial stem cells (SSCs) obtained from obstructive azoospermic (OA) and non-obstructive azoospermic (NOA) patients, and further, to characterize these cells for potential use in infertility treatment or study of reproductive biology.

MATERIALS AND METHODS

We have applied a cell-sorting method, using collagen and magnetic activated cell separation to overcome obstacles, developing a collection system, and simple long-term proliferation system, that yields large numbers of high-purity SSCs from obstructive OA and NOA patients.

RESULTS

SSCs derived from OA and NOA patients proliferated and maintained their characteristics for more than 12 passages (>6 months) in vitro. Moreover, the population of cells positive for the SSC-specific markers GFRalpha-1 and integrin alpha6, increased to more than 80% at passage 8.

CONCLUSION

These finding may support the idea that in vitro propagation of SSCs could be a useful tool for infertility treatment and study of reproductive biology.

In vitro culture and differentiation of buffalo (Bubalus bubalis) spermatogonia

The objective of this study was to develop a culture system which could support buffalo spermatogonia differentiation into spermatids in vitro. Testes from 3- to 5-month-old buffaloes were decapsulated and seminiferous tubules were enzymatically dissociated to recover spermatogonia and sertoli cells. The cells were cultured in modified Dulbecco modified Eagle medium supplemented with different concentrations of foetal bovine serum, retinol, testosterone for 2 months at 37 degrees C. Spermatogonia and sertoli cells were identified with an antibody against c-kit or GATA4, respectively. The viability of spermatogonia in the media supplemented with different concentrations of serum was all significantly higher (p < 0.05) compared with that in the medium without serum. A-paired or A-aligned spermatogonia and spermatogonial colonies (AP-positive) were observed after 7-10 days of culture and spermatid-like cells with a flagellum (6-8 microm) appeared after 30 days of culture. For cultured conditions, retinol could not significantly promote the formation of spermatid-like cells (p > 0.05), whereas supplementation of testosterone could significantly promote (p < 0.05) the formation of spermatid-like cells after 41 days of culture. The expression of the spermatid-specific marker gene (PRM2) was identified after 30 days of culture by RT-PCR. Yet, the transition protein 1 (TP1, a haploid makers) was not detected. Meanwhile, spermatids developed in vitro were also confirmed by Raman spectroscopy. These results suggest that buffalo spermatogonia could differentiate into spermatids in vitro based on the analysis of their morphology, PRM2 expression and Raman spectroscopy. Yet, the normality of the spermatid-like cells was not supported by TP1 expression.

Identification, localization, and sequencing of fetal bovine VASA homolog

The vasa gene, first described in Drosophila, is purported to be important in germ cell development. Vasa is present across several invertebrate and vertebrate taxa, including frogs, fish, chickens, and humans. Vasa, a DEAD (asparagine-glutamine-alanine-asparagine) box protein shown to function as an RNA helicase in vitro, has not been investigated previously in fetal stage cattle. Total RNA was extracted from bovine fetal gonads obtained at 35-55 days, 55-80 days, and 80-120 days of gestation to amplify a 296 bp reverse transcription polymerase chain reaction (RT-PCR) product using primers for human vasa. The complete coding sequence of bovine vasa was cloned with 5' and 3' random amplification of cDNA ends polymerase chain reaction (RACE-PCR) and subsequently identified as bovine vasa homolog (BVH). Northern blot analysis revealed that among the tissues examined (gonad, liver, heart, brain, and femur), the vasa gene was expressed in the gonad. This localization, the conserved pattern of gene expression, and the gene sequence suggests that BVH plays a role in bovine germ cell development as proposed for other mammalian species.

Spermatogenesis in immature mammals

Mammalian spermatogenesis has been studied extensively as a prime theme of male reproductive biology, especially for germ cell production, fertilization and development. Investigation of spermatogenesis has provided us with the opportunity to both study the male germ line stem cells and generate the transgenic animals. Spermatogenesis is conducted in the seminiferous tubules, which end in the rete testis. The organization of spermatogenesis means that the spermatogonia are uniformly distributed around the seminiferous tubules. The pubertal establishment and mature maintenance of spermatogenesis requires precursor cells. In bull testes at 4 weeks postnatal, gonocyte migration occurs and differentiated spermatogonia are recognized after 8 weeks. Within the period of 4-8 weeks of age, spermatogonial stem cell conversion and niche formation must occur. Spermatogonial stem cells are the only cells that can undergo self-renewal in spermatogenesis. Spermatogonial stem cell transplantation can potentially contribute to studies of gene expression during spermatogenesis and provide genetic progress in domestic animals. Bull spermatogonial stem cells have been demonstrated to be capable of colonizing recipient mouse seminiferous tubules. (Reprod Med Biol 2007; 6: 139-149).

In vitro differentiation of germ cells from nonobstructive azoospermic patients using three-dimensional culture in a collagen gel matrix

OBJECTIVE

To assess the effectiveness of the three-dimensional culture of spermatogenic cells in a collagen gel matrix from nonobstructive azoospermic patients and examine the relation between the success rate of in vitro spermatogenesis and serum FSH level as a diagnostic prediction.

DESIGN

Prospective study using radioimmunoassay, immunocytochemistry, and flow cytometry with primary cultured cells.

SETTING

Gynecologic clinics and human reproduction research laboratory.

PATIENT(S)

Primary culture of spermatogenic cells established from 18 nonobstructive azoospermic patients who underwent histologic diagnoses.

INTERVENTION(S)

Primary culture of spermatogenic cells in a collagen-based gel matrix, subjected to immunological and flow cytometric analyses.

MAIN OUTCOME MEASURE(S)

In vitro culture of spermatogenic cells was established in an extracellular milieu that more closely resembled the in vivo condition. The number of chromosomes in newly generated cells during culture was determined by fluorescence-activated cell sorter (FACS) and immunocytochemical analysis. Effects of FSH on the differentiation of the spermatogenic cells were measured.

RESULT(S)

Results of histologic studies indicated that 8 of 18 patients showed the spermatocyte arrest. Immunocytochemical and FACS analysis indicated that after 12 days in culture, haploid cells comprised 11%-37% of the cultured cell population with a characteristic expression of a cellular marker for spermatids. The serum level of FSH appeared to be closely correlated with an increase in the number of haploid cells in culture.

CONCLUSION(S)

The present three-dimensional culture in a collagen gel matrix provides a suitable means by which spermatocytes could be induced to differentiate into presumptive spermatids in vitro. In addition, the plasma FSH level could be a good indicator for the success of differentiation of cultured spermatogenic cells obtained from patients with spermatogenic arrest.

Evolution of DNA strand-breaks in cultured spermatocytes: The Comet Assay reveals differences in normal and γ-irradiated germ cells

In reproductive toxicity assessment, in vitro systems can be used to determine mechanisms of action of toxicants. However, they generally investigate the immediate effects of toxicants, on isolated germ cells or spermatozoa. We report here the usefulness of in vitro cultures of rat spermatocytes and Sertoli cells, in conjunction with the Comet Assay to analyze the evolution of DNA strand-breaks and thus to determine DNA damage in germ cells. We compared cultures of normal and gamma-irradiated germ cells. In non-irradiated spermatocytes, the Comet Assay revealed the presence of DNA strand-breaks, which numbers decreased with the duration of the culture, suggesting the involvement of DNA repair mechanisms related to the meiotic recombination. In irradiated cells, the evolution of DNA strand-breaks was strongly modified. Thus our model is able to detect genotoxic lesions and/or DNA repair impairment in cultured spermatocytes. We propose this model as an in vitro tool for the study of genotoxic injuries on spermatocytes.

Establishment of ovarian reconstruction system in culture for functional genomic analysis

In a previous study, we reported a list of genes expressed differentially in primordial and primary follicles [Park et al., Fertil. Steril., 83, 410-418 (2005)]. An innovative experimental system is required to evaluate the functions of these genes in folliculogenesis, particularly primordial-primary follicle transition. In this study, ovarian tissues were dissociated, and isolated cells were transfected using small interfering RNAs (siRNAs) for disrupting a specific gene, followed by ovarian reconstruction via calcium alginate encapsulation. The effects of RNA interference (RNAi) on follicular development were evaluated by a histological observation of the reconstructed ovarian tissue. Interestingly, follicular formation and development showed differences between control and experimental groups. Thus, even though this system includes some problems that need to be solved, ovarian reconstruction following the modification of gene expression of individual ovarian component cells could lead the way to methods of studying molecular mechanisms of primordial-primary follicle transition.

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.

Successful long term culture of immature porcine sertoli cells in the reconstructed testicular cell cord

The ultimate goal of this study was to establish an in vitro system to produce sperms. To pursue this goal, immature porcine testicular cells were cultured in stereostructural form and cultured testicular cord was investigated morphologically. At 4 weeks of age, the seminiferous tubules of the porcine testes consisted of undifferentiated germ cells (gonocytes and undifferentiated spermatogonia) and immature Sertoli cells. The interstitial tissue was largely occupied by Leydig cells. The testes were enzymatically digested, and the dispersed cells were encapsulated with alginate either immediately or after freeze-thawing. The resulting testicular cell cords were cultured for up to 10 weeks. After 2 weeks of culture, Sertoli cells, which were identified by their inhibin-positive reaction in immunohistochemistry, and Leydig cells, which were identified by their morphological characteristics, were observed in the cords. Neither undifferentiated nor differentiated types of germ cells were detected. The number of cells in the cords progressively decreased during the culture period. In order to discover the fate of the Sertoli cells, the level of inhibin in the spent media was determined. Inhibin in the media was at a detectable level after 2 days of culture. The levels increased and peaked at 2 weeks. When frozen-thawed testicular cells were applied to the culture, the peak level was maintained for over 8 weeks, in contrast to the gradual decrease of inhibin level when fresh cells were cultured. These results indicate that the culture conditions can sustain the survival of Sertoli cells. Further improvement is required for proliferation and differentiation of germ cells.

β-nerve growth factor participates in an auto/paracrine pathway of regulation of the meiotic differentiation of rat spermatocytes

NGF appears to be involved in spermatogenesis. However, mice lacking NGF or TrkA genes do not survive more than a few days whereas p75(NTR) knockout mice are viable and fertile. Therefore, we addressed the effect of betaNGF on spermatogenesis by using the systems of rat germ cell culture we established previously. betaNGF did not modify the number of Sertoli cells, pachytene spermatocytes, secondary spermatocytes nor the half-life of round spermatids, but increased the number of secondary meiotic metaphases and decreased the number of round spermatids formed in vitro. These effects of betaNGF were reversible and maximal at about 4 x 10(-11) M. Conversely, K252a, a Trk-specific kinase inhibitor, enhanced the number of round spermatids above that of control cultures. The presence of betaNGF and its receptors TrkA and p75(NTR) was investigated in testis sections, in Sertoli cell and germ cell fractions, and in germ cell and Sertoli cell co-cultures. betaNGF was detected only in germ cells from pachytene spermatocytes of stages VII up to spermatids of stages IX-X. TrkA and p75(NTR) were detected in Sertoli cells and in these germ cells. Taken together, these results indicate that betaNGF should participate in an auto/paracrine pathway of regulation of the second meiotic division of rat spermatocytes in vivo.

Spermatogonial stem cell transplantation and testicular function

Spermatogonial stem cells (SSCs) are responsible for the continual production of spermatozoa throughout adult life. Interactions between SSCs and the surrounding cells in the seminiferous tubules regulate the biological activity of these cells. Factors involved in the regulation of SSCs are beginning to be defined by animal models and the culture of SSCs in defined media. A critical development in the characterization of SSCs has been the development of the germ cell transplantation technique, which provides the only assay for the presence of SSCs in a population of cells, and which allows the determination of whether SSCs are proliferating or differentiating in culture. This approach has accelerated SSC-focused research and promises to provide a better understanding of the factors and mechanisms that regulate these cells. The knowledge provided by this work is also critical to an appraisal of the components of the SSC niche in the seminiferous epithelium. Thus, many aspects of testicular function can be defined by the investigation of SSCs and the factors, cells, and environment that regulate SSCs, thereby leading to a more comprehensive understanding of spermatogenesis.

Isolation of male germ stem cell-like cells from testicular tissue of non-obstructive azoospermic patients and differentiation into haploid male germ cells in vitro

BACKGROUND

The purpose of this study was to establish the culture conditions required to isolate, identify and expand male germ stem cell-like cells (GSC-LC) from the testicular tissue of patients with non-obstructive azoospermia (NOA).

METHODS AND RESULTS

Testicular tissues obtained from patients (two with maturation arrest (MA, n = 2) and Sertoli cell-only syndrome (SCOS, n = 11) were dissociated and plated into gelatin-coated dishes. After 2-4 weeks, cultures from both MA patients (100%) and four SCOS patients (36.3%) exhibited multicellular colonies, which proliferated successfully until passage 10. GSC-LC in the colonies displayed alkaline phosphatase activity, as well as Oct-4 and integrin b1 expression after every passage. After the fifth passage, GSC-LC were differentiated by encapsulation in calcium alginate and further cultivation. At 2 and 6 weeks, cells expressed c-Kit, Scp3, testis-specific histone protein 2B (TH2B), and transition protein (TP)-1. Fluorescence in situ hybridization additionally disclosed a few tetraploid and haploid cells at 6 weeks. Human oocytes were activated in the absence of artificial activation and cleaved after the injection of presumptive spermatids.

CONCLUSIONS

Our novel culture system may be useful for diagnosing the existence of germ cells and facilitating the treatment of NOA patients.

Isolation and viability of presumptive spermatids collected from bull testes by Percoll density gradient

The objective of the present study was to develop a procedure for isolating pure populations of round spermatid(s) (RS) by Percoll density gradient from bull testes. Bull testes were de-capsulated and testicular tissues were dissociated enzymatically to recover RS. After being filtered through a 20 microm nylon mesh, the cells were centrifuged at 650 x g for 25 min through the discontinuous Percoll density gradients (20, 35, 40, 45 and 90% Percoll solution). Isolated cells were analyzed by microscopic observation for survivability and apoptosis. In Experiment 1, both microscopic observation and DNA analysis by flow cytometry showed that approximately 40% of cells collected from 35% Percoll gradient were presumptive RS, whereas in 40% Percoll gradient, mostly primary spermatocytes were observed. Experiment 2 compared the effect of 35% Percoll density isolation on the incidence of apoptosis and necrosis in fresh and frozen-thawed cells to those of untreated cells. The percentage (mean+/-S.E.M.) of necrosis in cells collected from 35% Percoll gradient was less (P<0.05) than in untreated and frozen-thawed cells from 35% Percoll gradient (11.7+/-3.1% compared with 26.3+/-2.0% and 53.5+/-1.3%, respectively), but the rate of apoptosis did not differ (1.2+/-0.49% compared with 2.5+/-0.8% and 0.9+/-0.04%, respectively). The proportional data (mean+/-S.E.M.) of live cells in Percoll treated group were greater (P<0.05) than in untreated and frozen-thawed cells from the 35% Percoll gradient (86.7+/-3.26% compared with 70.8+/-2.73% and 41.9+/-1.69%, respectively). Experiment 3 compared the development rates of embryos injected with RS isolated from fresh and frozen-thawed cells collected with the 35% Percoll gradient to those of untreated cells, and parthenotes as control. There were no significant (P>0.05) differences in the rates of cleavage and blastocyst development between untreated fresh cells and fresh cells collected from the 35% Percoll gradient (75.4 and 10.5% compared with 82.4 and 12.8%). However, there were lesser (P<0.05) cleavage and blastocyst rates in frozen-thawed cells from the 35% Percoll gradient (51.6 and 6.3%) and parthenotes (60.7 and 4.1%) were observed. These results suggest that isolation of presumptive RS by 35% Percoll density gradient is effective in eliminating apoptotic and early necrotic cells. However, the use of RS in improving the developmental potential of embryos merits further studies.