SIX5 is a homeodomain transcription factor that functions as a developmental regulator involved in organogenesis, particularly in eye and muscle development 1. As a member of the Six4/5 family, SIX5 regulates transcription by binding specific DNA motifs and interacting with Eya protein cofactors 2. During human embryogenesis, SIX5 protein accumulates in myogenic cells and is translocated to nuclei during later myogenic differentiation stages, suggesting roles in differentiation rather than early myogenic activation 2. SIX5 is required for proper ventral body wall closure and abdominal muscle development, as evidenced by omphalocele formation in Six4/Six5 double-knockout mice, reflecting impaired growth and morphological changes in primary abdominal wall tissues 3. In ocular tissues, SIX5 is expressed in corneal epithelium, lens epithelium, ciliary body, retina, and sclera in adult eyes but not fetal eyes, implicating it in adult-onset cataract development in myotonic dystrophy 1. Recent single-cell analysis identified SIX5 as a putative transcriptional regulator of plasma cell maturation in tonsillar lymphoid tissue 4. Mutations in SIX5 cause branchiootorenal syndrome 2, highlighting its clinical importance in human developmental disorders.