G9a and ZNF644 physically associate to suppress progenitor gene expression during neurogenesis

Proliferating progenitor cells undergo unidirectional changes in competence to give rise to post-mitotic progeny of specialized function. These transitions in cell fate typically involve the dynamic regulation of gene expression programs by histone methyltransferase (HMT) complexes. However, the composition, roles and regulation of these HMT complexes in regulating cell fate decisions in vivo are poorly understood. Using affinity purification and mass spectrometry (AP-MS), we identified the uncharacterized C2H2-like zinc finger (ZF) protein ZNF644, which is putatively causally linked to high-grade (degenerative) myopia, as a novel G9a/GLP-interacting protein and co-regulator of histone methylation. Using zebrafish embryos, we characterized the function of two ZNF644 orthologues, znf644a and znf644b, revealing critical neural- specific roles in regulating G9a/H3K9me2-mediated gene silencing in the retina. In addition, by virtue of additional non-overlapping requirements for znf644a and znf644b during retinal differentiation, we gained further insights regarding additional facets of retinal differentiation regulated by the G9a-ZNF644 physical association, such as maintaining retinal cell viability and in transitioning proliferating progenitor cells towards differentiation. Collectively, our data points to the G9a-ZNF644 physical interaction as a critical neural progenitor-specific co-factor of G9a/H3K9me2-mediated gene silencing during neuronal differentiation. Examination of histone modifications in 2 ZNF644a/b mutants versus wildtype.