AMPK modulates a DEAH box RNA-helicase to attenuate TOR signaling and establish developmental quiescence in Caenorhabditis elegans

Abstract

Developmental plasticity allows organisms to adapt to environmental stress and improve reproductive fitness. Caenorhabditis elegans adapts to starvation and other stressors by transiting through an alternate developmental stage called dauer, which allows them to remain quiescent for several months, and yet fully retain reproductive fitness when they resume development. The AMP-activated protein kinase (AMPK) is essential for animals to passage through the dauer stage without reproductive consequence. The loss of AMPK leads to germline hyperplasia, dramatically reduced post-dauer fertility, and shortened dauer survival. We identified a putative RNA-binding helicase (HZL-1) that is targeted by AMPK. Disabling HZL-1 function rescues many dauer and post-dauer reproductive defects typical of the AMPK mutants. HZL-1 shares significant similarity with the conserved HELZ family of RNA helicases, possessing characteristic DEAH helicase motifs, a predicted ATP binding motif, and intrinsically disordered regions that are crucial for its localization and function. Curiously, HZL-1 is expressed and exerts its function in the intestine, yet its elimination suppresses the aberrant germ cell proliferation while restoring germline quiescence and subsequent post-dauer fertility in AMPK mutants. CLIP-seq data revealed that HZL-1 binds several mRNAs during the dauer stage, and thus when it is active in AMPK mutants, its regulation of these RNAs contributes to germline hyperplasia in the dauer germ line. The most enriched RNA bound and inhibited by HZL-1, argk-1, promotes fertility by suppressing TOR activity in the germ line of dauer larvae, thereby preserving germline quiescence. These findings underscore the intricate role of RNAs and RNA-binding helicases in the complex interplay of genetic signals that animals have acquired to ensure their effective transit through periods of environmental challenge.