Sox6, jack of all trades: a versatile regulatory protein in vertebrate development.

Approximately 20,000 genes are encoded in our genome, one tenth of which are thought to be transcription factors. Considering the complexity and variety of cell types generated during development, many transcription factors likely play multiple roles. Uncovering the versatile roles of Sox6 in vertebrate development sheds some light on how an organism efficiently utilizes the limited resources of transcription factors. The structure of the Sox6 gene itself may dictate its functional versatility. First, Sox6 contains no known regulatory domains; instead, it utilizes various cofactors. Second, Sox6 has a long 3'-UTR that contains multiple microRNA targets, thus its protein level is duly adjusted by cell type-specific microRNAs. Just combining these two characteristics alone makes Sox6 extremely versatile. To date, Sox6 has been reported to regulate differentiation of tissues of mesoderm, ectoderm, and endoderm origins, making Sox6 a truly multifaceted transcription factor.