Testis cord differentiation after the sex determination stage is independent of Sox9 but fails in the combined absence of Sox9 and Sox8

Abstract

Sox9 and Sox8 are transcription factors expressed in embryonic and postnatal Sertoli cells of the mouse testis. Sox9 inactivation prior to the sex determination stage leads to complete XY sex reversal. In contrast, there is normal embryonic testis development in Sox8 mutants which are initially fertile, but later develop progressive seminiferous tubule failure and infertility. To determine whether Sox9 is required for testis development after the initial steps of sex determination, we crossed Sox9(flox) mice with an AMH-Cre transgenic line thereby completely deleting Sox9 in Sertoli cells by E14.0. Conditional Sox9 null mutants show normal embryonic testis development and are initially fertile, but, like Sox8(-/-) mutants, become sterile from dysfunctional spermatogenesis at about 5 months. To see whether Sox8 may compensate for the absence of Sox9 during embryonic testis differentiation, we generated a Sox9 conditional knockout on a Sox8 mutant background. In the double mutants, differentiation of testis cords into seminiferous testis tubules ceases after P6 in the absence of one Sox8 allele, and after P0 in the absence of both Sox8 alleles, leading to complete primary infertility. Sox9,Sox8 double nullizygous testes show upregulation of early ovary-specific markers and downregulation of Sertoli intercellular junctions at E15.5. Their very low Amh levels still cause complete regression of the Müllerian duct but with reduced penetrance. This study shows that testis cord differentiation is independent of Sox9, and that concerted Sox9 and Sox8 function in post E14.0 Sertoli cells is essential for the maintenance of testicular function.

Germline stem cells are critical for sexual fate decision of germ cells

“…The mutant also indicated that sox9b expression is more intense in the supporting cells surrounding the germline stem cell population than in those that surround the gametogenesis‐committed germ cells 24. The function of germ cell maintenance has also been reported in the mouse adult testis 52. It is speculated that the loss of sox9b function in the germ cell maintenance, in addition to the loss of germline stem cells, allows for the neofunctionalization of the mammalian Sox9 as an effector of Sry .…”

Expression profile of the SOX9 gene in the testes of sexually immature and mature male goats (Capra hircus), and its potential influence on postnatal testis development

“…A deficiency in SOX9 expression in adult life may lead to various abnormalities, from gonadal dysgenesis to transdifferentiation into an ovary (Barrionuevo et al 2009;Barrionuevo et al 2012;Plotton et al 2012). Experiments on SOX9 conditional null mutant mice (Barrionuevo et al 2009) confirmed that SOX9 plays a crucial role in embryonic sex determination. Also, SOX9 together with SOX8 (SRY-box 8 gene) is essential for spermatic cord formation during early testis development.…”

“…However, the effects of these gene products on postnatal gonadal maturation, how their expression is regulated at different developmental stages, as well as their relationships with other factors are poorly understood. It is known that SOX9 plays a key role in the maintenance of testicular status in mice (Barrionuevo et al 2009;Barrionuevo et al 2012). A deficiency in SOX9 expression in adult life may lead to various abnormalities, from gonadal dysgenesis to transdifferentiation into an ovary (Barrionuevo et al 2009;Barrionuevo et al 2012;Plotton et al 2012).…”

“…It is known that SOX9 plays a key role in the maintenance of testicular status in mice (Barrionuevo et al 2009;Barrionuevo et al 2012). A deficiency in SOX9 expression in adult life may lead to various abnormalities, from gonadal dysgenesis to transdifferentiation into an ovary (Barrionuevo et al 2009;Barrionuevo et al 2012;Plotton et al 2012). Experiments on SOX9 conditional null mutant mice (Barrionuevo et al 2009) confirmed that SOX9 plays a crucial role in embryonic sex determination.…”

“…Also, SOX9 together with SOX8 (SRY-box 8 gene) is essential for spermatic cord formation during early testis development. The formation of the spermatic cord is fundamental to the maintenance of spermatogenesis in the adult testis, and its absence leads to infertility in adult males (Barrionuevo et al 2009;Jiang et al 2013). …”