Environmental Regulation of Reproductive System Development During the C. elegans Dauer Life Cycle

External conditions can alter an organism’s life history; understanding these developmental changes is increasingly important as the human environment is undergoing a period of rapid change. In response to the unfavorable conditions of crowding and starvation, C. elegans can form the morphologically distinct dauer larva, a long-lived diapause state that halts an animal’s development until conditions are more favorable for reproduction. Previous work discovered that different dauer induction protocols see differential recovery and post-dauer reproductive success. I hypothesized that differential recovery is preceded by cellular differences in the reproductive system during dauer itself. I found that different dauer induction methods lead to differences in the size of the dauer germline, with conditions producing larger dauer germlines also favoring a larger post-dauer brood. The key difference among the dauer induction methods that we tested is the duration of pre-dauer feeding, which is highly correlated with germline size in dauer. LAG-2, the pro-proliferative signal expressed by the germline stem cell niche that regulates germ cell divisions via Notch signaling, rapidly and dramatically decreases in abundance following withdrawal from food in the pre-dauer period. During dauer, LAG-2 remains low in the niche, and the germline is maintained in a Notch-independent state. Despite the initial fall in LAG-2 abundance being starvation-mediated, return to food is not required for the protein to rebound during the earliest part of dauer recovery, or for germ cells to re-enter the cell cycle and Notch-dependence to be restored. However, continued access to food during dauer recovery is required for continued divisions of germ cells and an exponential increase in LAG-2 protein. This protein increase is not associated with a corresponding increase in lag-2 transcription. Taken together, this work shows how developmental cues can be rapidly regulated in response to a fluctuating environment, with lasting consequences even after a more favorable environment is encountered. Future work will be concerned with determining the roles of dauer exit cues in reproductive system recovery following dauer and how they act on the yet-to-be-discovered molecular mechanism that regulates LAG-2 abundance.