Which transcription factor is activated by the SRY gene in mammals?
Sry encodes HMG-domain architectural transcription factor that does not itself complete Sertoli differentiation but initiates cascade by binding Sox9 testis-specific enhancer TESCO cooperatively with Sf1/Nr5a1. Protein induces DNA bending facilitating recruitment of coactivators, chromatin remodeling and sustained Sox9 transcription sufficient to commit supporting lineage. Sox9 fulfills most male functions including Fgf9, Amh induction and cord formation. Therefore immediate direct transcriptional target downstream of Sry is Sox9, functioning as hub for testis program. Other factors like Wnt4 and Foxl2 belong to opposing pathway suppressed.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: SRY activates SOX9 as primary target.