Loss of Etv5 Decreases Proliferation and RET Levels in Neonatal Mouse Testicular Germ Cells and Causes an Abnormal First Wave of Spermatogenesis1

Abstract

Mice that are ets variant gene 5 (ETV5) null (Etv5(-/-)) undergo the first wave of spermatogenesis but lose all spermatogonial stem cells (SSCs) during this time. The SSC loss in Etv5(-/-) mice begins during the neonatal period, suggesting a role for ETV5 in SSC self-renewal during this period. Herein, we show that Etv5 mRNA was present in perinatal mouse testis and that ETV5 was expressed in fetal Sertoli cells and by germ cells and Sertoli cells during the neonatal period. Transplantation of Etv5(-/-) germ cells failed to establish spermatogenesis in W/W(v) mice testes, indicating that germ cell ETV5 has a key role in establishment or self-renewal of transplanted SSCs. The SSC self-renewal is stimulated by glial cell-derived neurotrophic factor (GDNF) acting through the RET/GDNF family receptor alpha 1 (GFRA1) receptor complex in SSCs. Immunohistochemistry, quantitative PCR, and laser capture microdissection revealed decreased RET mRNA and protein expression in spermatogonia of neonatal Etv5(-/-) mice by Postnatal Days 4-8, indicating that disrupted GDNF/RET/GFRA1 signaling may occur before initial spermatogonial stem/progenitor cell decrease. Etv5(-/-) spermatogonia had reduced proliferation in vivo and in vitro. Decreased cell proliferation may cause the observed decreases in the number of type A spermatogonia (Postnatal Day 17) and daily sperm production (Postnatal Day 30) in Etv5(-/-) mice, indicating quantitative impairments in the first wave of spermatogenesis. In conclusion, ETV5 is expressed beginning in fetal Sertoli cells and can potentially have effects on neonatal Sertoli cells and germ cells. In addition, ETV5 has critical effects on neonatal spermatogonial proliferation, which may involve impaired signaling through the RET receptor.

Regulation of spermatogonial stem cell self-renewal and spermatocyte meiosis by Sertoli cell signaling

“…Regulation of early spermatogenesis by Sertoli cell signaling R161 expressed both in Sertoli cells (Chen et al 2005) and in SSCs (Oatley et al 2007, Tyagi et al 2009). Etv5-null germ cells fail to initiate spermatogenesis after transplantation into the testes of W/W v mice.…”

“…Etv5-null germ cells fail to initiate spermatogenesis after transplantation into the testes of W/W v mice. Specifically, a positive feedback loop involving ETV5 and GDNF/RET/ GFRA1 regulates SSC self-renewal (Tyagi et al 2009). Interestingly, a recent study has suggested that ETV5 directly activates the expression of microRNA-21 to regulate the self-renewal of mouse SSCs (Niu et al 2011).…”

Prepubertal human spermatogonia and mouse gonocytes share conserved gene expression of germline stem cell regulatory molecules

“…Three additional GDNFregulated genes, basic helix-loop-helix family, member e 40 (Bhlhb2), homeobox C4 (Hoxc4), and Tec protein tyrosine kinase (Tec) were validated in rat SSCs (11). Among these six genes, Bcl6b and Etv5 have now been identified as important by several studies and appear to play a central role in rodent SSC self-renewal (10)(11)(12)(13). GDNF also regulates downstream signaling and ultimately rodent SSC maintenance and self-renewal, which involves phosphatidylinositol 3-kinase/serine-threonine kinase AKT family (PI3K/AKT), and Src family kinase (SFK) signaling mechanisms (14)(15)(16).…”

Spermatogonial Stem Cells: An Alternate Source of Pluripotent Stem Cells for Regenerative Medicine

“…Although there have been no definitive culture conditions for propagation of either mouse or human SSCs, culture systems established by different groups seem to be conducive for their propagation. At least in rodents, glial cell line-derived neurotrophic factor (GDNF) was found to be essential to maintain SSCs in an undifferentiated state in vivo and in vitro (Tyagi et al 2009;Hofmann 2008;Sariola and Immonen 2008;Oatley, Avarbock, and Brinster 2007;Naughton et al 2006;Kubota, Avarbock, and Brinster 2004;Meng et al 2000).…”

“…Based on demonstrations of the importance of the stem cell niche (Tyagi et al 2009;de Rooij 2009;Hess et al 2006;Oatley, Racicot, and Oatley 2010), the pluripotential nature of SSCs and the instructive potential of various mesenchymes, we postulated and subsequently demonstrated that neonatal mouse SSCs could directly differentiate into prostatic, uterine and skin epithelium (Simon et al 2009) when recombined with the appropriate mesenchyme and grafted in vivo (Fig. 1).…”