Genetic Regulation Of Caenorhabditis Elegans Post Embryonic Development Involving The Transcription Factors Egl 38 Vab 3 And Lin 14

Abstract: Sequence-specific transcription factors are crucial to generating the gene expression patterns that drive the specification, morphogenesis, and physiology of organs and tissues. In order to better understand how organ form and function are orchestrated by transcription factors, we must better understand the genetic inputs and outputs of these critical regulators. In this work, I have utilized C. elegans to characterize the genetic networks and organ functions of three post-embryonically functioning transcription factors. The Pax family of transcription factors is highly conserved across animal species, and controls the development of multiple tissues and organs during development. In C. elegans males, two sensory mating structures, the copulatory spicules and the post-cloacal sensilla, are formed from stereotyped divisions of the two post-embryonic blast cells, B.a and Y.p, respectively. A C. elegans pax-6 transcript, vab-3, is necessary for the development of these sensory structures. Using a green fluorescent protein (GFP)-based vab-3 transcriptional reporter, I found that expression is restricted to the sensory organ lineages of B.a and Y.p. Transcription of vab-3 in the tail region of the worm requires the Abdominal-B homeobox gene, egl-5. Opposing this activation, a transcription factor cascade and a Wnt signaling pathway each act to restrict vab-3 expression to the appropriate cell lineages. Another C. elegans Pax gene, egl-38, is required for the development of the egg-laying system and rectum. However, few EGL-38 target genes are known. Using gene expression microarrays, we cross-referenced microarray data from an inducible EGL-38 strain and two egl-38 mutants that disrupt protein function in a tissue-preferential manner to identify potential tissue-specific EGL-38 target genes. One set of genes from this analysis was validated using GFP reporter transgenes. Most of these genes are expressed in egl-38-dependent tissues, and many display egl-38 dependence. In addition to the identification of target genes, this work revealed enrichments in gene classes that play a role in innate immunity. Consistent with this, we discovered a novel immune function for egl-38. We found that the gene activities of egl-38 and three egl-38-responsive genes from our validation set are associated with increased infection by the pathogenic bacterium M. nematophilum. However, we also show that egl-38 does not impact infection by a different pathogen, S. marcescens. While Pax genes regulate spatial tissue/organ identity, some transcription factors regulate temporal identity. In C. elegans, heterochronic genes function to ensure the precise timing of stage-specific developmental events. I positionally cloned a novel missense allele of the heterochronic transcription factor LIN-14, and revealed a previously undiscovered ability of this protein to solely affect late larval development. lin-14(sa485) hermaphrodites exhibit asynchrony between vulval and gonadal morphogenesis and maturation. Further, lin-14(sa485) preferentially disrupts the timing of vulval cell morphogenesis, but not cell division. I also show that terminal differentiation of a uterine cell type is delayed in lin-14(sa485) mutants.