Expression Profiles of SRY and SOX9 in Rabbit Gonads: The Classical Model of Mammalian Sex Differentiation

Sex determination in mammalian gonads depends on the concerted action of SRY and SOX at the genital ridge. Although most research on the mechanisms involved in sex determination has been done in mice, the study of non-model organisms may indicate the extent of the generalizations currently based on model systems. The present study investigated the correlation between SRY/SOX9 expression patterns and the process of morphogenesis in the developing gonad of the rabbit. In males, the onset of SRY/SOX9 expression closely followed the establishment of undifferentiated genital ridges at 13 to 14 dpc. In contrast to mouse, real-time PCR in the rabbit revealed that levels of SRY/ SOX9 peak after the onset of seminiferous cord formation, while in mouse this occurs before. Furthermore, rabbit gonads maintain low levels of SRY and SOX9 expression in male and female gonads, respectively. In situ hybridization suggests that cells of the mesonephric Bowman capsules, which do not express SRY, may become SOX9-expressing pre-Sertoli cells during the long period of seminiferous cord formation in the rabbit. In contrast to mouse, current results indicate that the patterns of SRY/SOX9 expression associated with the process of gonadal morphogenesis in rabbit appear similar to those of other mammals, including humans.