<i>Sox100B</i>, a <i>Drosophila</i> Group E Sox-domain Gene, Is Required for Somatic Testis Differentiation

Abstract

Sex determination mechanisms are thought to evolve rapidly and show little conservation among different animal species. For example, the critical gene on the Y chromosome, SRY, that determines sex in most mammals, is not found in other animals. However, a related Sox domain transcription factor, SOX9, is also required for testis development in mammals and exhibits male-specific gonad expression in other vertebrate species. Previously, we found that the Drosophila orthologue of SOX9, Sox100B, is expressed male-specifically during gonad development. We now investigate the function of Sox100B and find, strikingly, that Sox100B is essential for testis development in Drosophila. In Sox100B mutants, the adult testis is severely reduced and fails to interact with other parts of the reproductive tract, which are themselves unaffected. While a testis initially forms in Sox100B mutants, it fails to undergo proper morphogenesis during pupal stages, likely due to defects in the pigment cells. In contrast, no substantive defects are observed in ovary development in Sox100B mutant females. Thus, as is observed in mammals, a Sox9 homolog is essential for sex-specific gonad development in Drosophila, suggesting that the molecular mechanisms regulating sexually dimorphic gonad development may be more conserved than previously suspected.

Somatic gonadal cells: The supporting cast for the germline

“…1;DeFalco et al, 2008). These cells persist to adult stages and may perform an important signaling role during pupal development to promote testis morphogenesis (Nanda et al, 2009). Finally, by the end of stage 17, a critical structure that regulates the germline stem cells (GSCs), called the hub, forms from a group of 10-12 anterior SGPs, and this structure persists through adulthood ( Fig.…”

“…Sox100B is an ortholog of SOX9, which is necessary and sufficient for specification of the somatic Sertoli cells in mammals (DeFalco et al, 2003(DeFalco et al, , 2004Vidal et al, 2001;Wagner et al, 1994). However, in contrast to mouse SOX9, Sox100B is not required for msSGP specification (Nanda et al, 2009). In addition to some differences in gene expression between SGPs and msSGPs, msSGPs are also specified differently than SGPs.…”

“…These cells are derived from the fat body, and express Sox100B (DeFalco et al, 2008). While the exact role of these cells in regulating the germline is unknown, loss of Sox100B expression in the flies results in a severe reduction or loss of testes starting at pupal development, while ovaries appear normal (Nanda et al, 2009). Dwnt2 mutant adults exhibit a very similar phenotype (Kozopas et al, 1998); however, Dwnt2 is required in the embryo for pigment cell formation, while Sox100B is not required in the pigment cells until pupal stages (DeFalco et al, 2008;Nanda et al, 2009).…”

“…While the exact role of these cells in regulating the germline is unknown, loss of Sox100B expression in the flies results in a severe reduction or loss of testes starting at pupal development, while ovaries appear normal (Nanda et al, 2009). Dwnt2 mutant adults exhibit a very similar phenotype (Kozopas et al, 1998); however, Dwnt2 is required in the embryo for pigment cell formation, while Sox100B is not required in the pigment cells until pupal stages (DeFalco et al, 2008;Nanda et al, 2009). As both Dwnt2 and Sox100B mutant adults lack pigment cells and have testes that fail to undergo morphogenesis, it has been suggested that the pigment cells perform an important signaling role to promote testis morphogenesis (Nanda et al, 2009).…”

“…Dwnt2 mutant adults exhibit a very similar phenotype (Kozopas et al, 1998); however, Dwnt2 is required in the embryo for pigment cell formation, while Sox100B is not required in the pigment cells until pupal stages (DeFalco et al, 2008;Nanda et al, 2009). As both Dwnt2 and Sox100B mutant adults lack pigment cells and have testes that fail to undergo morphogenesis, it has been suggested that the pigment cells perform an important signaling role to promote testis morphogenesis (Nanda et al, 2009). The studies above describe some of the molecular mechanisms that regulate specification of the somatic cells of the gonad (Table 2).…”