The undifferentiated gonadal
primordium has the potential to develop into either a testis or an ovary. The
presence of SRY on the Y chromosome
triggers SOX9 upregulation which
drivestesticular development. SOX9 maintains its own expression by
forming two positive feedback loops with FGF9 and prostaglandin D synthase
which produces prostaglandin D2 (PGD2),
a hormone that reinforces SOX9
expression in Sertoli cells and contributes to the nuclear translocation of SOX9[1].
Sex determination pathways are highly
conserved between marsupials and eutherian mammals. However, unlike mice, the
relatively long period of marsupial gonadal differentiation as well as their
postnatal sexual differentiation offers a convenient model for studying the
gonadal differentiation and gene expression. We analysed the transcriptome of
developing tammar testes and ovaries and found that PDG2 is significantly upregulated in the testis at the time of gonadal
sex determination. We next examined the functional role of PGD2 in developing but
indifferent tammar gonads by culturing testes in the presence of a PGD2
synthesis inhibitor HQL-79, while ovaries were treated with exogenous PGD2.
After 5 days in culture, gonads were collected for morphological and molecular
analysis. Both HQL-79 treated testes and PGD2 treated ovaries showed changes in
SOX9 nuclear localization which was impaired in HQL-79 treated testes but in
cultured ovaries, exogenous PGD2 induced SOX9 translocation to the nucleus in
granulosa cells. Using RT-PCR, the sex determining genes SRY, SOX9, FGF9,
AMH, PTGDS and WNT4, were down-regulated in the HQL-79 treated
testes treatment, while SOX9 and FOXL2 were slightly increased. HQL-79
treated testes had a thick surface epithelium
while that of PGD2 treated ovaries was thin, These data suggest that
prostaglandin D2 plays a fundamental role in the regulation of SOX9 expression and nuclear translocation
in marsupials as it does in eutherians.