Transcription factor that is involved in the regulation of cell proliferation, apoptosis and embryonic development (By similarity). Plays an important role in the development of several organs, including kidney, muscle and inner ear (By similarity). Depending on context, functions as transcriptional repressor or activator (By similarity). Lacks an activation domain, and requires interaction with EYA family members for transcription activation (PubMed:15141091). Mediates nuclear translocation of EYA1 and EYA2 (PubMed:19497856). Binds the 5'-TCA[AG][AG]TTNC-3' motif present in the MEF3 element in the MYOG promoter and CIDEA enhancer (PubMed:27923061, PubMed:23435380, PubMed:15141091, PubMed:19497856). Regulates the expression of numerous genes, including MYC, CCND1 and EZR (By similarity). Acts as activator of the IGFBP5 promoter, probably coactivated by EYA2 (By similarity). Repression of precursor cell proliferation in myoblasts is switched to activation through recruitment of EYA3 to the SIX1-DACH1 complex (By similarity). During myogenesis, seems to act together with EYA2 and DACH2 (By similarity). Regulates the expression of CCNA1 (PubMed:15123840). Promotes brown adipocyte differentiation (By similarity). Interacts with DACH1 (By similarity). Interacts with EYA1 (By similarity). Interacts with EYA2 (PubMed:23435380, PubMed:19497856). Interacts with CDH1 (PubMed:17130831). Interacts with TBX18 (PubMed:26235987). Interacts with CEBPA (PubMed:27923061). Interacts with CEBPB (PubMed:27923061). Interacts with EBF2 (PubMed:27923061). Specifically expressed in skeletal muscle. Phosphorylated during interphase; becomes hyperphosphorylated during mitosis. Hyperphosphorylation impairs binding to promoter elements. Ubiquitinated by the anaphase promoting complex (APC), leading to its proteasomal degradation. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Defects in SIX1 could be a cause of branchiootorenal syndrome (BOR). BOR is an autosomal dominant disorder manifested by various combinations of preauricular pits, branchial fistulae or cysts, lacrimal duct stenosis, hearing loss, structural defects of the outer, middle, or inner ear, and renal dysplasia. Associated defects include asthenic habitus, long narrow facies, constricted palate, deep overbite, and myopia. Hearing loss may be due to mondini type cochlear defect and stapes fixation. Penetrance of BOR syndrome is high, although expressivity can be extremely variable. Belongs to the SIX/Sine oculis homeobox family.