Regulation and function of the Lhx gene, lin-11, in Caenorhabditis elegans nervous system development

Abstract

Lhx genes are a sub-family of Hox genes that play important roles in animal development. In Caenorhabditis elegans there are seven Lhx genes, including the founding family member lin-11. The lin-11 gene is necessary for the specification of neuronal and reproductive tissues. My thesis work has involved understanding the mechanism of lin-11 regulation and its function in these tissues. To this end, I addressed two distinct but complementary questions, one of which focused on how transcriptional regulation of lin-11 occurs and the second on the role of LIN-11 protein domains/regions. My work on the transcriptional regulation has uncovered important roles of two of the largest lin-11 introns, intron 3 and intron 7. These introns promote lin-11 expression in non-overlapping sets of amphid neurons. Based on gene expression patterns and behavioural assays, intron 3 is capable of restoring lin-11 function in lin-11(n389 ) null mutant allele. Comparison of intron 3-driven reporter expression in the neuronal cell types between C. elegans and C. briggsae has revealed cis and trans evolutionary changes in lin-11 regulation between the two species. Functional dissection of the introns in C. elegans has led to the identification of three distinct non-overlapping enhancers, each specific for a single amphid neuron, i.e., RIC, AIZ, and AVG. I have also identified four transcription factors, SKN-1, CEH-6, CRH-1, and CES-1, that act through these enhancers to regulate neuronal expression of lin-11. Furthermore, I have characterized the function of the LIM domains and a proline-rich (PRR) C-terminus region of LIN-11 in the specification of neuronal and reproductive tissues. My work shows that while the LIM domains are required for LIN-11 function in these tissues, the PRR region is dispensable. I have also examined the functional conservation of lin-11 domains using two other Lhx genes, Drosophila melanogaster (dLim1) and Mus musculus (Lhx1 ), and found that both of these genes were able to rescue lin-11 defects. Together, my work has significantly advanced our understanding of transcriptional regulation of lin-11, the importance of LIM domains in tissue formation, and functional conservation of Lhx genes across phyla.