The regulation of the Caenorhabditis elegans Hox gene egl-5 during the male tail development

Abstract

One of the most fundamental processes in the development of multi-cellular organisms is differentiation and cell fate specification. The Hox genes are a well-known group of segmental identity genes that confer positional information to the cells that express them. I have studied the regulation of the C. elegans Hox gene egl-5, as a model, to address the question of how Hox genes are regulated during development.;I have performed a promoter dissection study of egl-5, guided by the method of phylogenetic footprinting. I have located regulatory activities for individual tissues to short, conserved DNA fragments using reporters and tissue-specific rescue. We gave the name V6CRE ( V6 cis-regulatory element) to a 300bp conserved region, which can drive a reporter in wild-type egl-5 expression pattern in the seam cell V6 lineage, which generates the sensory rays in the male tail. Detailed analysis of the V6CRE region suggests that the regulation of egl-5 in the V6 lineage is an orchestration of multiple positive and negative pathways. Specifically, the V6CRE region encodes at least two redundant pathways, with important regulatory sites spreading over the whole region.;To identify direct regulators of egl-5 in the V6 lineage, I performed a yeast one-hybrid assay in search of the transcription factors that bind to V6CRE. I have recovered from the screen one clone corresponding to the SOX family gene sox-2. SOX family proteins are known regulators of neuronal development; members share a conserved SOX DNA binding domain. I have identified three potential binding sites of SOX-2 in V6CRE. Mutation of these sites disrupts one of the egl-5 regulating pathways inscribed in the V6CRE region, causing total loss of reporter expression in the V6 lineage. However, sox-2 is only expressed in the RnB neurons and structural cells of all the developing ray sublineages. Therefore, it is likely that SOX-2 is only one member of a group of proteins that recognize the same DNA motif and regulate egl-5 expression. Furthermore, ectopic expression of SOX-2 interferes with the normal development of the sensory rays, and is able to turn off an egl-5