Investigating Zmym2 and Zmym4 as Putative Six1 Co-Factors.

Branchio-oto-renal syndrome (BOR) is a condition that presents with variable craniofacial, otic, and/or renal malformations. Half of the BOR patients have a mutation in SIX1or its co-factor EYA1. As the other 50% of cases are of unknown cause, it is important to identify other putative co-factors of SIX1 that may contribute to BOR. A screen of the fly interactome identified zinc-finger MYM-containing proteins, Zmym2 and Zmym4, as putative co-factors of Six1. Recent studies have established that Zmym2 is a transcriptional repressor that interacts with Six4 during renal development. The function of Zmym4 has not yet been well characterized. In situ hybridization revealed that they are co-expressed with six1and eya1 in the pre-placodal ectoderm (PPE) and are later expressed in the otic vesicle (OV) and neural crest (NC) of Xenopus. Luciferase assays indicate that Zmym4 enhances Six1-Eya1 transcriptional activity whereas Zmym2 has a mild repressive effect. Loss of either Zmym2 or Zmym4 affects neural border, NC, and PPE marker genes, suggesting that both genes are important for craniofacial development. At later stages, loss of either Zmym2 or Zmym4 results in a reduction in the size of the OV as well as the branchial arch NC; the later results in altered craniofacial cartilages. Current experiments aim to decipher whether Zmym2 and Zmym4 interact with Six1 and/or Eya1 through co-immunoprecipitation experiments. Collectively, these data indicate that Zmym4 modulates Six1 transcriptional activity, Zmym2 and Zmym4 are required for craniofacial development, and suggests they may contribute to BOR phenotypes.