Diverse Genetic and Transcriptional Programs Mediate Dendrite Development of a Nociceptor Neuron

Abstract

Neurons are specialized cells that communicate through electrochemical signals: a neuron receives input through dendrites and sends information through a single axon. The receptive field for each neuron is defined by sister dendrites that occupy discrete domains. Two neurons in C. elegans, PVDL and PVDR, are model nociceptors for studying dendrite development because they exhibit an elaborate but well-characterized dendritic arbor that is readily visible beneath the skin. Previous studies of the PVD neuron showed that the LIM-homeodomain transcription factor MEC-3 is required for higher order dendritic branching. Microarray profiles of wild-type and mec-3 mutant animals identified targets of MEC-3 that may be involved in this developmental process. One of those targets, HPO-30/Claudin, was shown to be required for pioneer branch stabilization. Another target of MEC-3, the TFIIA-like zinc finger transcription factor EGL-46, was also found to be required for 2° branches, but the extent of the defect in egl-46 mutants was not as severe as those of mec-3. The work in this thesis explores the genetic pathways required for proper development of dendritic branches using the PVD nociceptive neuron as a model. Specifically, I found that EGL-46 works cell-autonomously in PVD to promote commissural 2° branches and that EGL-44 works with EGL-46 in this context. This EGL-44/EGL-46 pathway works in parallel to the previously reported HPO-30 pathway. In addition to being a target of MEC-3, EGL-46 is regulated by other factors as well. MEC-3 is also required for 1° branch length and axon length. Finally, I generated a strain that was optimal for isolating PVD neurons from worms by fluorescence-activated cell sorting (FACS). Additional targets of MEC-3 were identified from a differential expression analysis of mec-3 mutants versus wild-type worms using these FACS-isolated PVD cells. This dataset provides a foundation for future work on specific components downstream of MEC-3 that are required for dendrite development.