AMPK regulates germline stem cell integrity and quiescence through a mir-1/tbc-7/rab-7 pathway in C. elegans.

During periods of energetic stress, Caenorhabditis elegans can undergo a global quiescent stage known as "dauer". During this stage, all germline stem cells undergo G2 cell cycle arrest through an AMPK-dependent mechanism. In animals that lack AMPK signalling, the germ cells fail to arrest, undergo uncontrolled proliferation and lose their reproductive capacity. These germline defects are accompanied by an altered chromatin landscape and gene expression program. We identified an allele of tbc-7, a RabGAP protein that functions in the neurons, which when compromised, suppresses the germline hyperplasia in the dauer larvae, as well as the post-dauer sterility and somatic defects characteristic of AMPK mutants. This mutation also corrects the abundance and aberrant distribution of transcriptionally activating and repressive chromatin marks in animals that otherwise lack all AMPK signalling. We identified RAB-7 as one of the potential RAB proteins that is regulated by tbc-7 and show that the activity of RAB-7 is critical for the maintenance of germ cell integrity during the dauer stage. A singular small RNA, mir-1, was identified as a direct negative regulator of tbc-7 expression through the analysis of seed sequences on the 3UTR of tbc-7. Animals lacking mir-1 are post-dauer sterile, displaying a similar phenotype to AMPK mutants. Altogether, our findings describe a novel mir-1/tbc-7/rab-7 pathway occurring in the neurons that regulates the germ line in a cell non-autonomous manner.