Novel roles of C. elegans heterochromatin protein HP1 and linker histone HIS-24 in the regulation of innate immune gene expression and stress Response

Linker histone H1 and heterochromatin protein 1 (HP1) are essential components ofheterochromatin which contribute to the transcriptional repression of genes. It has been shown that the methylation mark on the histone H1 serves as a specific recognition code for the chromodomain of HP1, however, the functional role of the HP1/H1 complex remains elusive. Using C. elegans, we elucidate the function of the linker histone variant HIS-24 and heterochromatin proteins HPL/HP1 in the cooperative transcriptional regulation of immunerelevant and stress resistance genes. We also show that HIS-24 and HPL act redundantly in vulval cell fate specification and gonad development. Finally, we provide the first evidence that HPL-1 interacts with HIS-24 at mono-methylated lysine 14 and associates in vivo with promoters of infection-inducible genes: the caenacin (cnc)- and the thaumatin (thn)- gene clusters. Our results highlight a functional link between epigenetic regulation by HP1/H1 the innate immune system and stress response. The experiment was performed using biological independent replicates of pooled worms. For the KO mutants we used duplicates and for WT condition quadruplicates.