Analysis of Medaka sox9 Orthologue Reveals a Conserved Role in Germ Cell Maintenance

Abstract

The sex determining gene is divergent among different animal species. However, sox9 is up-regulated in the male gonads in a number of species in which it is the essential regulator of testis determination. It is therefore often discussed that the sex determining gene-sox9 axis functions in several vertebrates. In our current study, we show that sox9b in the medaka (Oryzias latipes) is one of the orthologues of mammalian Sox9 at syntenic and expression levels. Medaka sox9b affects the organization of extracellular matrices, which represents a conserved role of sox9, but does not directly regulate testis determination. We made this determination via gene expression and phenotype analyses of medaka with different copy numbers of sox9b. Sox9b is involved in promoting cellular associations and is indispensible for the proper proliferation and survival of germ cells in both female and male medaka gonads. Medaka mutants that lack sox9b function exhibit a seemingly paradoxical phenotype of sex reversal to male. This is explained by a reduction in the germ cell number associated with aberrant extracellular matrices. Together with its identified roles in other vertebrate gonads, a testis-determining role for Sox9 in mammals is likely to have been neofunctionalized and appended to its conserved role in germ cell maintenance.

Sox9 plays multiple roles in the lung epithelium during branching morphogenesis

“…Studies have shown that Sox9 plays critical roles in both ECM deposition and cell migration in various tissues and diseases (18). In the heart, Sox9 is required for proper organization the valvular ECM proteins (60), whereas in the gonads, Sox9 regulates many ECM proteins as well as modifiers of the ECM such as matrix metalloproteinases (61,62). Sox9 also plays a role in fibrotic and sclerotic disorders in various tissues, in which Sox9 causes excessive and inappropriate ECM deposition by activating ECM proteins (63)(64)(65)(66)(67)(68).…”

Analysis of a novel gene, Sdgc, reveals sex chromosome-dependent differences of medaka germ cells prior to gonad formation

“…We then asked whether the upregulation of Sdgc was due to the presence of a Y chromosome in germ cells or in somatic cells. To address this issue, we generated chimeric medaka by transplanting XY germ cells into XX hosts and vice versa (Nakamura et al, 2012b), using sox9b-DsRed/olvas-EGFP transgenic line as hosts and nontransgenic strains as donors. Prior to manipulation, the host germ cells with EGFP fluorescence were ablated by nanos3/cxcr4-morpholino injection.…”

“…To eliminate the host's germ cells, 2000 ng/µl cxcr4-MO and 1000 ng/µl nanos3-MO were injected into one-or two-cell stage embryos (Kurokawa et al, 2006(Kurokawa et al, , 2007. The transplantation procedure was performed as previously described (Nakamura et al, 2012b).…”

“…Sdgc ORF was amplified using FLAG-tagged primers and inserted into a SalI site of the pBLSK+ PTV1-2A-mCherry vector (Nakamura et al, 2012b). olvas-3′UTR was inserted into downstream of the mCherry by InFusion (Clontech, 639649) to generate FLAG:Sdgc:2A:mCherry:olvas-3′ UTR.…”

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

“…However, our recent analysis indicated that sox9b − an orthologue of the mammalian Sox9 expressed in the supporting cells − is not directly involved in testicular differentiation. A study utilizing a medaka sox9b mutant demonstrated that the function of sox9b is more related to the maintenance of germ cells 51. 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.…”