A Non-stop identity complex (NIC) supervises enterocyte identity and protects from pre-mature aging

Abstract

A hallmark of aging is the inability of differentiated cells to maintain their identity. In the aged Drosophila midgut differentiated enterocytes (ECs) lose their identity, and the integrity of the midgut tissue and its homeostasis are impaired. To discover regulators of EC identity relevant to aging we performed an RNAi screen targeting 453 ubiquitin-related genes in fully differentiated ECs. Seventeen genes were identified, including the de-ubiquitinase Non-stop (Not/dUSP22; CG4166). Acute loss of Non-stop in young ECs phenotypically resembled aged ECs. Lineage tracing experiments established that Non-stop-deficient young ECs as well as wild-type aged ECs are no longer differentiated. Aging or acute loss of Non-stop also resulted in progenitor cell hyperproliferation and mis-differentiation, loss of gut integrity, and reduced organismal survival. Proteomic analysis unveiled that Non-stop maintains identity as part of a Non-stop identity complex (NIC) that contains E(y)2, Sgf11, Cp190, (Mod) mdg4, and Nup98. Transcriptionally, Non-stop ensured chromatin accessibility at EC genes, maintained an EC-specific gene expression signature, and silenced non-EC-relevant transcriptional programs. Within the NIC, Non-stop was required for stabilizing of NIC subunits. Upon aging, the levels of Non-stop and NIC subunits declined, and the large-scale organization of the nucleus was distorted. Maintaining youthful levels of Non-stop in wildtype aged ECs safeguarded the protein level of NIC subunits, restored the large-scale organization of the differentiated nucleus, and suppressed aging phenotypes and tissue integrity. Thus, the isopeptidase Non-stop, and NIC, supervise EC identity and protects from premature aging.

Nuclear organization and regulation of the differentiated state

“…Indeed, loss of met-1 or mes-4 (the histone methylases that catalyzes H3K36me2/3) in the cec-4 mutant background resulted in displacement of an artificial repeat reporter from heterochromatin, similar to that observed upon loss of MRG-1.This demonstrates that the positioning of heterochromatin in differentiated cells involves the activity of MRG-1 and H3K36 methylases in euchromatin regions. Interestingly, the shRNA-mediated loss of dMES-4 in differentiated enterocytes (ECs) in the Drosophila midgut resulted in a loss of the differentiated identity of mature enterocytes, a decline in the expression of EC genes, and the ectopic expression of the intestinal stem cell marker Delta on the surface of EC-like cells [ 64 ].…”