SIX Homeobox Protein 3 (SIX3)

SIX3 shares 98% and 88% identity with the mouse and chicken Six3 proteins, respectively, and all 3 proteins have identical SIX and homeobox domains. Northern blot analysis revealed that the SIX3 gene was expressed as an approximately 3-kb mRNA only in the eye. In situ hybridization to fetal and adult human retinal tissues indicated that the SIX3 gene was expressed in the ganglion cells and in cells of the inner nuclear layer. This expression pattern was maintained in the fully differentiated eye. Six3 is involved in a process by which positional information is established at the anterior boundary of the developing mouse embryo. Six3 appears to be the mouse functional homolog of Drosophila 'so,' since the proteins share extensive sequence identity and Six3 is expressed during mouse eye development.