Kadekar, P. | Search bioRxiv

bioRxiv2021

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.

genetics↗

bioRxiv2018

AMPK regulates germline stem cell quiescence and integrity through an endogenous small RNA pathway.

C. elegans larvae can undergo a global developmental arrest following the execution of a diapause-like state called dauer in response to unfavourable growth conditions. Survival in this stage surpasses the normal lifespan of reproductive animals quite dramatically, and without any apparent negative impact on their reproductive fitness. During this period, the germ cells become quiescent and must retain their reproductive integrity so the animal can reproduce following recovery. This germline stem cell (GSC) arrest requires the activity of AMP-activated protein kinase (AMPK) and in its absence the germ line undergoes hyperplasia. We show here that AMPK mutant animals exhibit complete sterility after recovery from dauer, suggesting that germ cell integrity is compromised during this stage in the absence of AMPK. These defects correlate with altered abundance and distribution of a number of chromatin modifications that affect gene expression. These aberrant chromatin modifications, along with the supernumerary germ cell divisions and the observed post-dauer sterility, were all corrected by disabling key effectors of the small interfering RNA pathway (dcr-1 and rde-4) and the primary Argonaute protein ergo-1, suggesting that AMPK regulates the function of these small RNA pathway components, and in its absence, the pathways become abnormally active. The aberrant regulation of the small RNA pathway components releases the germ cells from quiescence to proliferative state thereby compromising germ cell integrity. Curiously, AMPK expression in either the neurons or the excretory system is sufficient to restore the GSC quiescence and the fertility in the AMPK mutant post-dauer adults, while the fertility of these animals is also partially restored by disabling the dsRNA importer SID-1. Our data suggest that AMPK regulates a small RNA pathway in the soma to establish and/or maintain GSC quiescence and integrity cell non-autonomously in response to the energy stress associated with the dauer stage. Our findings therefore provide a unique model to better understand how the soma communicates with the germ line to establish the appropriate epigenetic modifications required to adapt to acute environmental challenges.

developmental biology↗