Elucidating the Effects of Environmental and Physiological Conditions on Stem Cell Regulation In Vivo

The Notch signaling pathway is a highly conserved intercellular signaling pathway that any dysregulation can lead to a variety of human diseases. These diseases are further exacerbated by various environmental, pathological and genetic conditions. Previous studies have shown that these conditions have been known to affect the Notch transcriptional response. However, the molecular mechanisms by which such conditions influence Notch signaling remained largely unknown. Moreover, most Notch studies have relied on in vitro systems and indirect reporters, which can miss the dynamic and contextual nature of Notch signaling. Here, we systematically analyzed the effects of these conditions with single molecule resolution in vivo within Caenorhabditis elegans, where Notch maintains the germline stem cell (GSC) pool by activating the transcription of its target genes in a graded manner. We examined the spatiotemporal changes of Notch responses under varying developmentally and clinically important conditions, including diverse growth temperature, pathological Notch receptor mutations, and starvation. We re-classified the mutations based on their effects on Notch-induced transcriptional activation, and germline function and defined the relationship between the two categories, enabling the prediction of genetic and phenotypic traits of untested mutations. We also demonstrated that changes in temperature and dietary conditions distinctly affected the Notch transcriptional activation and activity. This research elucidated the molecular mechanisms by which critical environmental conditions influence Notch activation, with the potential for refining the efficacy of therapeutics for Notch-related diseases.