Spermatogonial stem cell (SSC) transplantation is an alternative reproductive method to achieve conservation and production of elite animals in livestock production. Creating a recipient animal without endogenous germ cells is important for effective SSC transplantation. However, natural mutants with depletion of SSCs are difficult to obtain, and drug ablation of endogenous germ cells is arduous to perform for practical use. In this study, we used mouse models to study the preparation of recipients with congenital germ cell ablation. We knocked out (KO) Ets-variant gene 5 (Etv5) in mice using the CRISPR/Cas9 system. The testicular weight of Etv5−/− mice was significantly lower than that of wild-type (WT) mice. The germ cell layer of the seminiferous tubules gradually receded with age in Etv5−/− mice. At 12 weeks of age, the tubules of Etv5−/− mice lacked almost all spermatogenic cells with a Sertoli cell-only phenotype, and sperm were completely absent in the epididymis. We subsequently transplanted allogeneic SSCs with enhanced green fluorescent protein (EGFP) into 3- (immature) or 7-week-old (mature) Etv5−/− mice. Partially restoration of germ cell layers in the seminiferous tubules and spermatogenesis was observed in all immature testes but not in mature adult testes at 2 months post-transplantation. The presence of heterologous genes Etv5 and EGFP in recipient testicular tissue and epididymal sperm by PCR indicated that sperm originated from the transplanted donor cells. Our study demonstrates that, although Etv5−/− mice could accommodate and support foreign germ cell transplantation, this process occurs in a quite low efficiency to support a full spermatogenesis of transplanted SSCs. However, using Etv5−/− mice as a recipient model for SSC transplantation is feasible, and still needs further investigation to establish an optimized transplantation process.

ABSTRACT. In this study, we developed a model of sperm in vitro differentiation to study the mechanism of spermatogenesis. We isolated newborn male germ cells for in vitro differentiation. We found that after 4-5 weeks of culture, sperm-like cells were occasionally observed in cell co-culture and the feed-layer. After 1-2 weeks of culture followed by 4-5 weeks of co-culture, sperm-like cells were observed.

Spermatogonial stem cell transplantation (SSCT) can restore male fertility through transfer of germline between donor and recipient males. From an agricultural perspective, SSCT could be an important next-generation reproductive and breeding tool in livestock production. Current SSCT approaches in large animals remain inefficient and many technical details need further investigation. This paper reviews the current knowledge on SSCT in large animals, addressing (1) donor spermatogonial stem cell (SSC) preparation, (2) recipient male treatment, and (3) SSC injection, homing, and detection. The major studies showing unequivocal evidence of donor SSC-derived spermatogenesis in large animals (mainly in livestock for breeding purpose) are summarized to discuss the current status of the field and future directions.

Spermatogonial stem cells (SSCs) are the only adult stem cells capable of passing genetic information to offspring through their ability to both self‐renew and differentiate into mature spermatozoa. SSCs can be transplanted to establish donor‐derived spermatogenesis in recipient animals, thus offering a novel reproductive tool for multiplication of elite individual animals to benefit livestock production. An optimal SSC culture in vitro can benefit various SSC‐based studies and applications, such as mechanistic study of SSC biology, SSC transplantation process and SSC‐based transgenesis technique. However, except for some model rodent animals, SSC culture remains an inefficient and unstable process. We here studied a workflow to isolate, purify and in vitro culture porcine SSCs from neonatal pig testes. Pig testicular cells were dissociated by two‐step enzymatic digestion with collagenase type IV and trypsin. We enriched the spermatogonia from the testicular cell mix by differential plating for at least 3 times to remove firmly attached non‐SSCs. We then tested the optimal culture medium formula by supplementation of different growth factors to the basic medium (DMEM/F12 + 1% FBS) and found that a combination of 20 ng/ml GDNF, 10 ng/ml LIF, 20 ng/ml FGF2 and 20 ng/ml IGF1 had the best effect on SSC growth in our defined experimental system. In the presence of 4 growth factors without specific feeders, the purified SSCs can be cultured in poly‐L‐lysine‐ and laminin‐coated dishes for 28 days and remain preserving a continuous proliferation without losing the undifferentiated spermatogonial phenotype.

Spermatogonial stem cell (SSC) self-renewal is an indispensable part of spermatogenesis. Angiotensin I-converting enzyme (ACE) is a zinc dipeptidyl carboxypeptidase that plays a critical role in the regulation of the renin-angiotensin system. In this study, we used reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis to confirm that somatic ACE (sACE), but not testicular ACE (tACE), is expressed in mouse testis before postpartum day 7 and in cultured SSCs. Our results revealed that sACE is located on the membrane of SSCs. Treating cultured SSCs with the ACE competitive inhibitor captopril was found to inhibit sACE activity, and significantly reduced the proliferation rate of SSCs. Microarray analysis identified 651 genes with significant differential expression. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these differentially expressed genes are mainly involved in the mitogen-activated protein kinase (MAPK) signaling pathway. sACE was found to play an important role in SSC self-renewal through the regulation of MAPK-dependent cell proliferation.