Date of Award

Summer 7-28-2017

Degree Type

Thesis

Degree Name

Master of Science in Integrative Biology (MSIB)

Department

Biology

Committee Chair/First Advisor

Carol Chrestensen

Major Professor

Martin Hudson

Second Committee Member

Lisa Ganser

Abstract

In order to survive, an organism must be able to receive, integrate, and respond to sensory stimuli. However, the cellular basis of sensory perception and response is difficult to study in complex animals such as humans, and is therefore poorly understood. The nematode Caenorhabditis elegans is a relatively simple organism yet displays many distinct behaviors, making it an ideal system to understand the relationship between gene function, cell shape, cell physiology, and behavioral output. Much of the thermosensory and chemosensory information that the nematode receives from its sensory neurons is processed via a pair of interneurons called AIYL and AIYR. In wild-type animals, the AIY cell bodies lie just posterior to the pharynx, and extend an anterior process that contacts its contralateral partner at the base of the nerve ring. The AIYL and R processes then diverge and extend around the nerve ring, ultimately making contact again on the dorsal side of the animal via a gap junction. We previously showed that the Eph receptor tyrosine kinase VAB-1 is required for AIY cell body placement and ventral AIYL/R contact. Conversely, the ephrin EFN-4 is required for dorsal AIYL/R connectivity. We have extended these studies and show that the AIYL/R ventral contact is mediated via the ephrin gene efn-1. In addition, we show that this connectivity requires both VAB-1 kinase activity and also a non-kinase dependent VAB-1 function. Preliminary tissue specific rescue experiments suggest that the development of the ventral gap is partially cell-autonomous.

To integrate AIYL/R morphology and function with behavior, we are using WormLab software to image and analyze EphR/ephrin mutants both on and off food. Wild-type animals search for food using long “runs” interspersed with reversals and ~170-degree “omega” turns. We find that vab-1 mutants lack the ability to perform straight runs, although they can perform omega turns normally. Instead, they display a strong circling locomotion, both on and off food. When EphR/ephrin pathway mutants are conditioned in a 150mM NaCl environment with food, then assayed on a food-free NaCl gradient, vab-1, efn-1 and efn-4 mutants all display normal chemotaxis towards a point NaCl source, suggesting no overt defects with NaCl conditioning and chemotaxis. We are currently investigating neuromuscular junction morphology in EphR and ephrin mutants to see if this correlates with dorsal versus ventral locomotion bias. We are also investigating the Ca2+ signaling in the AIY interneuron in order to determine whether defects in connectivity between the AIYL and AIYR affect synaptic transmission.

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