SOHLH1 and SOHLH2 coordinate spermatogonial differentiation

Abstract

Spermatogonial self-renewal and differentiation are essential for male fertility and reproduction. We discovered that germ cell specific genes Sohlh1 and Sohlh2, encode basic helix-loop-helix (bHLH) transcriptional regulators that are essential in spermatogonial differentiation. Sohlh1 and Sohlh2 individual mouse knockouts show remarkably similar phenotypes. Here we show that SOHLH1 and SOHLH2 proteins are co-expressed in the entire spermatogonial population except in the GFRA1+ spermatogonia, which includes spermatogonial stem cells (SSCs). SOHLH1 and SOHLH2 are expressed in both KIT negative and KIT positive spermatogonia, and overlap Ngn3/EGFP and SOX3 expression. SOHLH1 and SOHLH2 heterodimerize with each other in vivo, as well as homodimerize. The Sohlh1/Sohlh2 double mutant phenocopies single mutants, i.e., spermatogonia continue to proliferate but do not differentiate properly. Further analysis revealed that GFRA1+ population was increased, while meiosis commenced prematurely in both single and double knockouts. Sohlh1 and Sohlh2 double deficiency has a synergistic effect on gene expression patterns as compared to the single knockouts. SOHLH proteins affect spermatogonial development by directly regulating Gfra1, Sox3 and Kit gene expression. SOHLH1 and SOHLH2 suppress genes involved in SSC maintenance, and induce genes important for spermatogonial differentiation.

NOTCH signaling in Sertoli cells regulates gonocyte fate

“…For instance, RBPJ target genes such as Hey1 and Heyl were upregulated in Sertoli cells, as expected; in germ cells, Nanos2, a gene that suppresses meiosis, 54 was downregulated, and genes that are expressed at the beginning of or during meiosis, such as Stra8 and Rec8, 55,56 were all upregulated (GSE37073). Furthermore, in accord with the observation that germ cell differentiation had taken place, a significant decrease in Pou5f1 (a marker for undifferentiated spermatogonia) 57 and a significant increase in Sohlh2 (a marker for differentiating spermatogonia) 58 were also found in these mutant germ cells. Our molecular analyses demonstrated that these effects correlated with a downregulation of Sertoli cell-specific factors that are essential to maintaining the undifferentiated state of germ cells.…”

Transcriptional control of KIT gene expression during germ cell development

“…In vitro experiments further showed that SOHLH1 and SOHLH2 can independently and cooperatively bind a bHLH binding site containing probe designed on discrete sequences of the Kit transcriptional regulatory regions. Finally, by chromatin immunoprecipitation (ChIP) analysis, SOHLH1 was found to occupy discrete bHLH binding site containing regions within the Kit promoter in spermatogonia chromatin (Barrios et al, 2012;Suzuki et al, 2012). Moreover, the human SOHLH1 gene, but not a deletion mutant associated to non-obstructive azoospermia, was previously shown to transactivate the human Kit promoter in transfection experiments (Choi et al, 2010).…”

“…Good candidates were two bHLH transcription factors specifically expressed in germ cells, SOHLH1 (Spermatogenesis and Oogenesis HLH1) and SOHLH2. Both SOHLHs have been involved in the differentiation of spermatogonia and oocytes (Ballow et al, 2006a;Ballow et al, 2006b;Hao et al, 2008;Pangas et al, 2006;Toyoda et al, 2009;Suzuki et al, 2012). In the male, deletion of each transcription factor leads to the disappearance of KIT-expressing spermatogonia in the prepuberal testis, whereas, in the female, both SOHLH1 and SOHLH2 ablations are responsible of oocyte loss in the neonatal ovary.…”

The mammalian Doublesex homolog DMRT6 coordinates the transition between mitotic and meiotic developmental programs during spermatogenesis

“…A number of transcriptional regulators also have been shown to play essential roles in controlling spermatogonial differentiation, including the basic helix-loop-helix (bHLH) proteins SOHLH1 and SOHLH2, and the DMRT protein DMRT1 (Ballow et al, 2006;Hao et al, 2008;Matson et al, 2010;Suzuki et al, 2012). DMRT proteins are transcription factors that bind DNA via the DM domain, a structurally distinct class of zinc-finger motif (Erdman and Burtis, 1993;Zhu et al, 2000).…”