Rhox13 Is Translated in Premeiotic Germ Cells in Male and Female Mice and Is Regulated by NANOS2 in the Male1

Abstract

Male and female germ cells enter meiosis in response to an extrinsic cue by retinoic acid (RA), but the pathways downstream of RA signaling that regulate early gametogenesis remain uncertain. We identified a novel reproductive homeobox gene, Rhox13, transcribed in the prenatal ovary and testis beginning on Embryonic Day (E) 13.5. Translation of RHOX13 also begins in female germ cells on E13.5 but is suppressed in male germ cells until Postnatal Day 3. Translation of RHOX13 coincides with initiation of RA signaling in both male and female gonads in vivo but occurs precociously in neonatal testes exposed to RA in vitro or in fetal male germ cells when NANOS2 is absent in vivo. Conversely, RHOX13 translation in female germ cells is suppressed in the presence of ectopically induced NANOS2. These results strongly suggest that RHOX13 expression is regulated at a posttranscriptional step by direct interaction of NANOS2 with Rhox13 mRNA to suppress translation.

The Homeobox Transcription Factor RHOX10 Drives Mouse Spermatogonial Stem Cell Establishment

“…We ruled out Rhox3 and Rhox13 as likely to be involved, as they are expressed in later stage germ cells than SSCs (Geyer et al, 2012; Song et al, 2015). Likewise, Rhox11 and Rhox12 are also unlikely to be responsible, as their postnatal expression pattern is consistent with primary expression in spermatids (Maclean et al, 2005).…”

Dynamic expression pattern and subcellular localization of the Rhox10 homeobox transcription factor during early germ cell development

“…This would not be entirely surprising, as the translation of many transcripts has been shown to be subject to regulation at different points of development in both male and female germ cells (Hecht 1998). Indeed, recently it has been reported that a member of Rhox gene cluster, Rhox13, is translationally repressed by the RNAbinding protein, NANOS2, in gonocytes and early spermatogonia (Geyer et al 2011). However, unlike RHOX13, RHOX10 is not translationally repressed in gonocytes but instead is highly expressed in these cells (Fig.…”

Rhox13 is required for a quantitatively normal first wave of spermatogenesis in mice

“…In the male, it is transcribed solely in germ cells throughout testis development, and mRNAs are detectable from E12.5 through adulthood (Geyer and Eddy 2008, Geyer, et al 2012). However, RHOX13 protein is only readily detectable in spermatogonia and preleptotene spermatocytes, is decreased dramatically in leptotene spermatocytes, and is undetectable in pachytene spermatocytes and spermatids (despite both cell types containing abundant Rhox13 mRNA) (Geyer and Eddy 2008, Geyer, et al 2012). To test the hypothesis that RHOX13 plays an essential role in male germ cell development, we took a reverse genetics approach to disrupt the Rhox13 gene.…”

“…However, RHOX13 protein is only readily detectable in spermatogonia and preleptotene spermatocytes. We found that Rhox13 mRNAs are repressed in prospermatogonia through a direct interaction with the RNA binding protein NANOS2, and this repression is apparently alleviated in response to RA (Chappell, et al 2013, Geyer, et al 2012). This translational control in the testis results in a protein expression pattern for RHOX13 that is remarkably similar to that in the female (oogonia/spermatogonia and preleptotene oocytes/spermatocytes), although they seem to be determined by distinct mechanisms.…”

“…IHC was performed as previously described (Geyer, et al 2012). Briefly, Bouin’s-fixed testis sections were deparaffinized and then RHOX13 antiserum (generated previously, (Geyer and Eddy 2008)) was applied at 1:500 for 1 h at room temperature without antigen retrieval.…”