SET-9 and SET-26, the C. elegans homologs of human MLL5, are critical for germline development and longevity

SET-9 and SET-26 are highly homologous paralogs that share redundant function in germline development, but SET-26 alone plays a key role in longevity and heat stress response. SET-26 is broadly expressed, but SET-9 is only detectable in the germline, which likely account for their different biological roles. SET-9 and SET-26 bind to H3K4me3 in vitro and in vivo, and their loss results in broadening of H3K4me3 domains. SET-9 and SET-26 also regulate the RNA expression of a subset of their target genes, irrespective of their H3K4me3 status. We propose that SET-9 and SET-26 function to organize local chromatin environment and to regulate the expression of specific target genes, and these activities together contribute to their critical roles in germline development, stress response, and longevity. SET-9 and SET-26 are highly homologous to human MLL5, a factor implicated in leukemia and glioblastoma, and our findings help to provide new insights into MLL5. H3K4me3 in N2 and set-9 set-26; and SET-9/26 ChIP; RNA-seq for N2, set-9, set-26 and set-9 set-26