Sry and Sox9: mammalian testis-determining genes

Sry is the Y-chromosomal gene that acts as a trigger for male development i n mammalian embryos. This gene encodes a high mobility group (HMG) box tran scription factor that is known to bind to specific target sequences in DNA and to cause a bend in the chromatin. DNA bending appears to be part of the mechanism by which Sry influences transcription of genes downstream in a c ascade of gene regulation leading to maleness, but the direct targets of Sl y remain to be positively identified. One gene known to be downstream from Sry in this cascade is Sox9, which encodes a transcription factor related t o Sty by the HMG box. Like Sry, mutations in Sox9 disrupt male development, but unlike Sry, the role of Sox9 is not limited to mammals. This review fo cuses on what is known about the two genes and their likely modes of action , and draws together recent data relating to how they might interconnect wi th the network of gene activity implicated in testis determination in mamma ls.