Date of Award
neuronal identity, transcriptional regulation, C. elegans, NSY-7 protein, AWC neurons
Maintenance of cell identity is a complex process that depends on developmentally determined transcriptional states and on environmental input. In neurons, which are both highly differentiated and highly sensitive to external stimuli, maintenance of identity is especially challenging. In this thesis, I describe the isolation and characterization of several genes involved in maintaining the identities of two olfactory neuron subtypes, AWCON and AWCOFF, in the nematode Caenorhabditis elegans. The AWCON and AWCOFF identities are specified by a stochastic decision during embryogenesis, but several of the genes involved in this embryonic decision are subsequently downregulated. Additional mechanisms must therefore act to maintain the AWCON and AWCOFF cell fates. I cloned and characterized a transcription factor, nsy-7, that was required to maintain expression of the AWCON marker str-2. nsy-7 mutants also misexpressed the AWCOFF marker srsx-3 in both AWCs. The chemotaxis phenotype of these mutants indicated that their defects in str-2 and srsx-3 expression corresponded to a more general change in cell identity from AWCON to AWCOFF. nsy-7 expression was restricted to AWCON by the signaling pathway that controls the initial fate decision. I collaborated with the Bulyk lab to discover a specific seven-nucleotide DNA sequence bound by the NSY-7 protein. This sequence was present in the srsx-3 promoter and required for NSY-7-mediated repression of srsx-3 in AWCON. Using this sequence, I was also able to predict new transcriptional targets of NSY-7. In a screen to identify additional genes affecting maintenance of str-2 and srsx-3 expression, I isolated nineteen mutants, including the uncharacterized conserved transcription factor hmbx-1 and components of the TGF! pathway. I showed that TGF! signaling is required continuously in adults to maintain srsx-3 expression and depends on dauer pheromone, an external sensory cue. I then identified new AWCON- and AWCOFF-specific markers and examined the extent to which changes in expression of str-2 or srsx-3 correlate with larger-scale changes in gene expression in the two AWC neurons. Together, my results indicate that several interlocking genetic pathways combine to maintain the AWCON and AWCOFF cell identities, including several factors not previously known to be involved in this process.
Lesch, Bluma J., "Mechanisms for Maintaining Cell Identity in C.elegans Olfactory Neurons" (2010). Student Theses and Dissertations. 67.