Transcription factor SOX-18 is a member of the SOX (SRY-related HMG-box) family of transcription factors involved in the regulation of embryonic development and in the determination of the cell fate. The encoded protein may act as a transcriptional regulator after forming a protein complex with other proteins. This protein plays a role in hair, blood vessel, and lymphatic vessel development. Greenfield et al. (1996) described a novel member of the mouse Sox gene family, Sox18, which is transcribed in adult lung and in cardiac and skeletal muscle. They reported that the Sox18 protein binds the sequence AACAAAG in vitro and that it is capable of transactivating gene expression. Pennisi et al. (2000) found that Sox18 is expressed in the developing vascular endothelium and hair follicles in mouse embryos.