Bioscientifica Proceedings

In mammals, testicular differentiation is initiated by SRY (the sex-determining region of the Y chromosome) gene expression in Sertoli cell precursors, followed by upregulation of the SOX9 gene (SRY-related HMG box gene 9). Subsequently, differentiated testis produces two hormones that induce sexual differentiation of the internal and external genital tract. Knowledge of the molecular mechanisms involved in gonadal differentiation has increased greatly over the past decade. Several genes are involved in genital ridge formation in both sexes, and others act specifically in testicular or ovarian developmental pathways. As for other mammals, relatively few data are available on the first steps of ovarian differentiation in pigs. In this review, the expression profiles of most genes known to be involved in gonadal differentiation in pigs will be presented and compared with those observed in mice. The main feature of gonadal differentiation in the pig is fetal steroidogenesis, especially cytochrome P450 aromatase gene organization and expression. Another specific feature of gonadal differentiation in pigs is the appearance of numerous cases of XX sex-reversed animals. This intersex condition occurs as early as day 50 after coitus, during embryogenesis, and appears to be triggered genetically. It leads to a wide range of phenotypes, strikingly similar to those observed in humans. Identification of the genes involved in this pathology will improve our knowledge of mammalian gonadal differentiation and may allow the eradication of this genetic disease in pigs.

© 2001 Society for Reproduction and Fertility