The role of suv4-20h1 in Xenopus multiciliogenesis [ATAC]
Histone post-translational modifications (PTM) greatly influence gene expression and are widely considered to regulate progression through development. However, the function of some PTMs remain elusive. H4K20 is sequentially methylated in concert with the cell cycle. In proliferating cells, SET8/KTM5A writes the monomethyl mark in G2/M phase, which then is converted to the di- and trimethylated states by SUV4-20H1/H2 (KMT5B/KMT5C) methyltransferases in the next G1 and S phase. In quiescent, differentiated cells, H4K20me2 represents the most abundant histone modification present in vertebrate chromatin. To address the function of H4K20 methyl states in development, we blocked the deposition of H4K20me2 and H4K20me3 by depleting the SUV4-20H1 in Xenopus embryos. This results in a severe ciliogenic defect in multiciliated cells (MCCs), as well as the repression of hundreds of cytoskeleton and cilium related genes. Further, we demonstrate that this defect can be rescued by wildtype, but not catalytically inactive SUV4-20h1, as well as by overexpressing PHF8, an H4K20me1-specific histone demethylase. Ciliogenic defects cannot be rescued by master regulators of ciliogenesis on the phenotypic or transcriptional levels. Taken together, this indicates that SUV4-20H1 plays a critical role in multiciliogenesis. Overall design: To investigate the effect of suv4-20h1 knockdown on Xenopus animal caps, we injected embryos with translation blocking morpholinos again suv4-20h1 and cut epidermal explants (animal caps).  At NF 16, we harvested animal caps and performed ATAC-seq to profile changes in chromatin accessibility upon suv4-20h1 depletion.