Reverse transcription-polymerase chain reaction analysis of genes involvedin gonadal differentiation in pigs

In mammals, testis development is initiated in the embryo as a response to the expression of the sex-determining gene, SRY. The time course of SRY exp ression during gonadal differentiation in the male has been described in de tail only in mice and sheep. In this study, we used reverse transcription-p olymerase chain reaction analysis to define the SRY transcription profile i n pig genital ridges. SRY transcripts were first detectable from 23 days po stcoitum (dpc), then declined sharply after 35 dpc. None were detected at 6 0 dpc, In addition, we analyzed temporal expression of other genes known to be involved in mammalian sex determination: WT-1, SF-1, SOX9, and AMH. A k ey stage seems to be 28 dpc, in which SOX9 expression switches between the male and female, and AMH expression begins to attest to Sertoli cell differ entiation and to correspond to seminiferous cord formation in the male. Exp ression of gonadotropin receptors and aromatase was also investigated in po rcine gonads, and we showed that their transcripts were detected very early on, especially in the male: 25 dpc for the LH receptor (rLH) and aromatase , and 28 dpc for the FSH receptor (rFSH), In the female, aromatase transcri pts were not detected until 70 dpc, and rFSH expression occurred later: at 45 dpc at the onset of meiosis. Moreover, no difference was observed betwee n the sexes for the onset of rLH transcription at 25 dpc. Such a thorough s tudy has never been performed on pigs; developmental analysis will be usefu l for investigating sex-reversed gonads and determining ontogeny in interse xuality, a common pathology in pigs.