Characterizing Hey2 as a Six1-Interacting Protein

Abstract

Branchio-oto-renal spectrum disorders (BORSD) are a type of congenital hearing loss disorders found in roughly 2% of profoundly deaf children. BORSD not only affects ear development, but also has the potential to cause other developmental defects such as branchial fistulae and cysts in the neck, as well as renal abnormalities. So far, mutations in two genes, SIX1 and EYA1, have been found to be the primary contributors to BORSD, but these still only account for 44% of those who suffer from this disorder. In recent years, researchers have worked to identify other genes involved in the SIX1 developmental pathway, particularly cofactors that may modulate the activity of SIX1 and EYA1 and could contribute to the wide variability of symptoms observed in BORSD patients. HEY2 is one of these potential cofactors that has been identified using a yeast 2-hybrid screen, but further studies are required to determine if it truly has a role as a SIX1 cofactor. Using Xenopus laevis as a model organism, we conducted in situ hybridization on embryos to discover that hey2 is partially coexpressed with six1 during larval stages of development, pointing to a possible interaction in vivo. Additionally, luciferase assays have shown that Hey2 increases Six1 transcriptional activity in vitro, potentially by strengthening the Six1- Eya1 interaction. Further research is needed to determine if this increase in activity is due to direct binding of Hey2 and Six1, but our early findings show that Hey2 is a promising Six1 cofactor that may contribute to BORSD.