Zmym2 Alters Expression of Key Craniofacial Genes

To identify novel Six1-interacting proteins, we previously screened the fly interactome for Sine oculis-binding partners whose orthologues are also expressed in Xenopus embryos. We identified a zinc-finger MYM-containing protein—Zmym2—based on its sequence similarity in a few domains also found in the Drosophila and vertebrate Sine oculis-binding proteins (Sobp). Because recent studies established Zmym2 as a transcriptional repressor that interacts with Six4 during renal development, herein we assessed whether it interacts with Six1, can modify Six1's transcriptional activity, and is involved in cranial neural crest or placode gene expression. Although during early development Zmym2 is expressed in many of the same tissues as Six1 and contains several domains also found in Sobp, we did not detect any interaction by co-immunoprecipitation and did not detect any effect on Six1 + Eya1 transcriptional activity in cultured cells. Nonetheless, increasing the level of Zmym2 in embryos resulted in broader expression domains of neural border, neural tube and neural crest genes, and smaller placode gene domains. These results suggest that although Zmym2 is unlikely to be a bone fide Six1 interacting protein, it appears to indirectly antagonize Six1 function during cranial placode development, promoting neural plate and neural crest gene expression.