Bridging Sensory Perception to Developmental Decision Making in Caenorhabditis elegans

Citation

Zhang, Mark Guangde (2024) Bridging Sensory Perception to Developmental Decision Making in Caenorhabditis elegans. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/hf7p-aa22. https://resolver.caltech.edu/CaltechTHESIS:05212024-230922611

Abstract

Amidst uncertain environmental flux, organisms must be able to appropriately adapt their physiology in response to or in preparation for harsh conditions. To accomplish this task, organisms need to accurately perceive current environmental cues, make informed decisions about how the future environmental landscape might unfold, and execute the genetic programs to manifest the proper physiological changes. As a prime example, the roundworm Caenorhabditis elegans makes multiple developmental decisions during its life cycle in response to environmental cues. During larval growth, C. elegans can forego reproductive growth and instead enter diapause (also called dauer), a developmentally arrested state resistant to environmental stress, in response to unfavorable growth conditions. The decisions to enter and exit dauer involve complex neurogenetic computations that integrate environmental cues, yet despite decades of research in the field of C. elegans dauer biology, we still do not fully understand how such sensory integration occurs. Furthermore, how the dauer entry and exit decisions compare and contrast to one another remains unclear.

In this thesis, I comprehensively analyze the C. elegans dauer exit decision using behavioral analyses, neuronal imaging, and gene reporter technologies. In Chapter Two, I I demonstrate how, during dauer exit, the ASJ chemosensory neurons integrate food availability and population density at both the levels of neuronal calcium dynamics and gene expression. I show that expression of the insulin-like peptide encoding gene ins 6 within the ASJ neurons is responsive to dauer-relevant cues, dependent on ASJ neuronal activity, and participates in an autoregulatory feedback mechanism that enforces decision commitment. In Chapter Three, I analyze how steroid hormones are essential for the dauer exit decision, and I illustrate how the spatiotemporal dynamics of steroid hormone regulation during dauer exit compares with that of dauer entry. Taken together, this thesis significantly advances our knowledge of the C. elegans dauer exit decision and helps us better understand how animals coordinate decisions over long timescales in response to changing environments.

Thesis Files