HP1 can act independently of H3K9 methylation to promote heterochromatin focus formation, gene repression, and organogenesis [CUT&Tag]

Here, we report H3K9me-independent functions for the HP1 orthologue HPL-2 and the H3K9 methyltransferase MET-2/SETDB1 in C. elegans. Both proteins co-localize in H3K9me-containing sub-nuclear foci independently.

Their combined loss additively disrupts gene repression and organogenesis. HPL-2 remains functional in the absence of H3K9me: HPL-2 deficient for H3K9me-binding still localizes to heterochromatin foci, restricts cell fate decisions and represses developmental genes. MET-2, catalytically active or not, requires the disordered protein LIN-65 to form foci and silence genes in vivo, while HPL-2 requires a multi-zinc finger ligand, LIN-13.