Intestinal Mg2+ accumulation induced by cnnm mutations decreases the body size by suppressing TORC2 signaling in Caenorhabditis elegans

Mg2+ is a vital ion involved in diverse cellular functions by forming complexes with ATP. Intracellular Mg2+ levels are tightly regulated by the coordinated actions of multiple Mg2+ transporters, such as the Mg2+ efflux transporter, cyclin M (CNNM). Caenorhabditis elegans (C. elegans) worms with mutations in both cnnm-1 and cnnm-3 exhibit excessive Mg2+ accumulation in intestinal cells, leading to various phenotypic abnormalities. In this study, we investigated the mechanism underlying the reduction in body size in cnnm-1; cnnm-3 mutant worms. RNA interference (RNAi) of gtl-1, which encodes a Mg2+-intake channel in intestinal cells, restored the worm body size, confirming that this phenotype is due to excessive Mg2+ accumulation. Moreover, RNAi experiments targeting body size-related genes and analyses of mutant worms revealed that the suppression of the target of rapamycin complex 2 (TORC2) signaling pathway was involved in body size reduction, resulting in downregulated DAF-7 expression in head ASI neurons. As the DAF-7 signaling pathway suppresses dauer formation under stress, cnnm-1; cnnm-3 mutant worms exhibited a greater tendency to form dauer upon induction. Collectively, our results revealed that excessive accumulation of Mg2+ repressed the TORC2 signaling pathway in C. elegans worms and suggest the novel role of the DAF-7 signaling pathway in the regulation of their body size.