Ancestral function of Inhibitors-of-kappaB regulates Caenorhabditis elegans development

Mammalian I{kappa}B proteins (I{kappa}Bs) exert their main function as negative regulators of NF-{kappa}B, a central signaling pathway controlling immunity and inflammation. An alternative chromatin role for I{kappa}Bs has been shown to affect stemness and cell differentiation. However, the involvement of NF-{kappa}B in this function has not been excluded. NFKI-1 and IKB-1 are I{kappa}B homologs in Caenorhabditis elegans, which lacks NF-{kappa}B nuclear effectors. We found that nfki-1 and ikb-1 mutants display developmental defects that phenocopy mutations in Polycomb and UTX-1 histone demethylase, suggesting a role for C. elegans I{kappa}Bs in chromatin regulation. Further supporting this possibility (i) we detected NFKI-1 in the nucleus of cells; (ii) NFKI-1 and IKB-1 bind to histones and Polycomb proteins, (iii) and associate with chromatin in vivo, and (iv) mutations in nfki-1 and ikb-1 alter chromatin marks. Based on these results, we propose that ancestral I{kappa}B inhibitors modulate Polycomb activity at specific gene subsets with an impact on development.