Understanding Chemotaxis in the Nematode Caenorhabditis elegans

How animal behavior is controlled at the molecular and cellular levels is still largely mysterious. Here, I document my studies on the mechanisms controlling a simple behavior--chemotaxis--in the nematode worm Caenorhabditis elegans. My work focuses on a pair of amphid sensory neurons at the head end of the worm called ASEs. The neurons are exposed and respond to environmental chemical signals, and instruct downstream locomotory responses that cause the worm to move up or down chemical gradients. The ASE neurons are morphology similar and arranged symmetrically across the head. Yet, it has been known for some time that they show differences in which ionic signals they are primarily responsive to (Na+/, Cl/, K+) in regards to chemotaxis behavior. Furthermore, it had been observed that the ASEs also express distinct sets of genes, in particular, receptor-type guanylyl cyclases (rGCs). This thesis begins with my contribution to a study of the function of ASE asymmetry in chemotaxis. I, along with another graduate student, found that an additional four salt ions (Br-, Li+/, I /, Mg2+) are sensed by either ASER (right) or ASEL (left) neurons. Evidence is presented that this laterality i