"Investigation of Reproductive Inhibition during Chronic Heat Stress in" by Macy Makenna Nielander

Date of Award

12-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical Engineering and Sciences

First Advisor

Timothy A. Crombie

Second Advisor

Melissa Borgen

Third Advisor

Robert van Woesik

Fourth Advisor

Linxia Gu

Abstract

Nearly all organisms experience heterogeneity in environmental conditions that can negatively impact fitness. A common adaptive strategy to reduce the impact of this stress is called facultative diapause, where development and reproduction are temporarily arrested to promote survival. Facultative diapause is characterized by three major criteria, the arrest must be (i) induced by an unfavorable environmental condition, (ii) reversible, and (iii) driven by genetically regulated mechanisms. The aim of this thesis was to determine whether chronic heat-induced inhibition of egg laying in Caenorhabditis elegans represents a novel form of facultative diapause. It was found that the inhibition of egg-laying is rapidly induced after 16 hours of heat stress, and is reversible upon return to control conditions for exposures extending up to 24 hours. Unlike another form of reproductive diapause in C. elegans, this work showed that the cessation of egg-laying is not regulated by the gene nhr-49. Heat-induced damage was also investigated as a potential driver of the shutdown. Multiple cellular damage phenotypes were observed in the gonad prior to and immediately after shutdown, with mixed reversibility during recovery. Notably, most phenotypes observed after shutdown do not reverse alongside arrest, potentially indicating a purely correlative relationship. Overall, it remains unclear whether genetic factors, cellular damage, or a combination of both drive the inhibition of egg-laying during chronic heat stress in C. elegans. Further studies will determine whether the shutdown represents a novel form of reproductive diapause, and may ultimately lead to a better understanding of how organisms navigate environmental stress.

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