Demoinet, Emilie et al. (2011) International Worm Meeting "Function of AMPK during the L1 diapause in C.elegans."

Mantovani, Julie, Roy, Richard, Demoinet, Emilie

[International Worm Meeting, 2011]

During periods of prolonged nutrient stress, many organisms undergo developmental or reproductive diapause, which are reversible states of developmental dormancy. When starved, Caenorhabditis elegans can arrest at multiple points during development. The best characterized of these are the first larval stage (L1) and dauer diapauses. C. elegans L1 hatchlings can survive up to 2 weeks in the absence of food but do not initiate post-embryonic development- therefore this L1 arrest is a response to an insufficient level of nutrient to initiate postembryonic development, whereby development is suspended without obvious long-term morphological modification. We have shown that the maximal survival in the L1 diapause requires aak-2, one of the 2 homologues of the alpha subunit of AMP-activated protein kinase (AMPK). AMPK is a metabolic master switch that is activated in response to various nutritional and stress signals. Its main function is to maintain cellular energy homeostasis by up-regulating pathways that produce ATP; while down-regulating energy-consuming anabolic processes. To better understand the role of AMPK in L1 diapause, we identified targets of these protein kinases using both genetic and biochemical strategies. Using differential 2D gel electrophoresis (DiGE) coupled with MS/MS we identified a number of endoplasmic reticulum (ER) proteins that were differentially expressed and phosphorylated between WT and aak-2 mutant larvae. The ER regulates calcium homeostasis and the synthesis of secretory proteins, while it is also the site for important maturation steps, including proper folding of nascent polypeptides. The efficiency of this folding depends on appropriate cellular conditions. Various stimuli collectively referred to as ER stress, such as ischemia, hypoxia, oxidative stress, and Ca2+ depletion, can lead to the accumulation of unfolded or misfolded proteins in the ER. This activates an adaptative signaling cascade known as the unfolded protein response (UPR). Our data suggest that AMPK regulates the UPR as a result of ER stress during the L1 diapause. We are currently investigating the molecular mechanisms that underlie this AMPK-mediated regulation.

Frezal, Lise et al. (2017) International Worm Meeting "Some C. elegans wild isolates display a heat-triggered mortal germ line phenotype."

Braendle, Christian, Frezal, Lise, Demoinet, Emilie, Felix, Marie-Anne, Miska, Eric, Zhang, Gaotian

[International Worm Meeting, 2017]

The mortal germ line phenotype was defined by Ahmed and Hodgkin as a multigenerational phenotype, whereby a selfing C. elegans line becomes sterile after several generations (1). The N2 reference strain does not display this phenotype, but Ahmed and Hodgkin could isolate mutants that are mortal. Some of these mutations are temperature-sensitive and affect small RNA and chromatin modification pathways, which may explain the multigenerational nature of the phenotype (e.g. 2,3). We discovered serendipitously that many C. elegans wild isolates display a strong mortal Germ Line (Mrt) phenotype: chronic exposure to high temperature, e.g. 25 deg C, progressively leads to sterility within several generations. Here we discuss this surprising finding. We first assayed a reference panel of 97 C. elegans wild isolates (4) for their Mrt phenotype, scoring the number of generations at 25 deg C after which full sterility occurred. Wild isolates showed strong, reproducible differences. We found no association between the severity of the Mrt phenotype and the climatic origin of C. elegans isolates. In the generations before full sterility, we observed a progressive brood size decrease, germ line differentiation defects, chromosomal aberrations at diakinesis and DNA damage. The mortal germline phenotype was however fully reversed by switching back from 25 deg C to 15 deg C before the last generation. Most surprisingly, germline immortality of some isolates was rescued by artificial infection with Nematocida microsporidia, natural intracellular C. elegans pathogens infecting intestinal cells, which suggests signaling from soma to germline. We suggest that the Mrt phenotype observed under laboratory conditions is likely not commonly displayed under natural conditions, yet provides an exciting model to test whether and how epigenetic inheritance systems are modulated by natural genetic variation. In order to pinpoint the molecular inheritance system underlying this mortal phenotype, we focused on determining the genetic basis of the quantitative variation among the C. elegans wild isolates, using both association mapping and laboratory crosses. The two approaches yielded three candidate regions, which we confirmed through introgression experiments. Thus, although the multigenerational nature of the Mrt phenotype may stem from inheritance of small RNAs and chromatin marks that are temperature-sensitive, phenotypic variation in the Mrt phenotype among C. elegans wild isolates is due to genetic variation. (1) Ahmed & Hodgkin. 2000. Nature; (2) Ashe et al. 2012 Cell; (3) Buckley et al. 2012 Nature; (4) Andersen et al. 2012 Nature Genetics.