Zmym2 and Zmym4 Act as Co‐Factors of Six1 During Craniofacial Development

Abstract

Branchio-oto-renal syndrome (BOR) is an autosomal dominant condition that presents with variable cranial, otic, and renal malformations. However, only half of BOR cases have a known genetic cause: mutations in the genes encoding Six1 and its co-factor Eya1. Therefore, it is important to identify other proteins that may interact with either Six1 or Eya1 that could be involved in the craniofacial phenotypes involved in BOR patients. In a screen for potential new cofactors, we identified Zinc Finger MYM-containing 2 (Zmym2) and Zmym4, whose expression overlaps with Six1 the pre-placodal ectoderm and otic vesicle; they also are expressed in the cranial neural crest and branchial arches. Knockdown of Zmym2 or Zmym4 resulted in a broader but less intense expression of msx1, pax3 and tfap2 in the neural border zone at neural plate stages, and expanded neural crest (foxD3, sox9) and placode (six1) genes at neurula stages. At larval stages, dlx5 expression in the neural crest and otic vesicles were reduced. Luciferase assays demonstrate that Zmym2 reduces Six1-Eya1 transcriptional activation whereas Zmym4 enhances it. These data indicate that Zmym2 and Zmym4 serve an important role in the development of craniofacial tissue, including the otic vesicle, and suggest they may have a role in BOR.