Profiles

Eva Nokes

Graduate Student

enokes [at] brandeis.edu

The ability of C. elegans to sense multiple chemical signals in their environment is mediated by individual chemosensory neuron subtypes, each of which senses a unique subset of chemicals, and expresses a defined subset of chemoreceptor and other signaling genes. We are interested in understanding the transcriptional rules that govern the expression of chemosensory genes specifically in individual sensory neuron subtypes. We selected the AWB neurons for our study since we have identified a set of AWB-selective chemoreceptors and other genes via expression profiling from isolated AWB neurons (Colosimo et al., 2004).

a) The promoter of sru-38 fused to GFP shows expression in the AWB as well as ASH pair of chemosensory neurons. b) When four base pairs in the same GFP fusion are mutated, GFP expression in lost specifically in the AWB neurons.

Using deletions and point mutations, I have now identified cis-regulatory motifs driving AWB-specific expression in the promoters of several chemoreceptor genes. Interestingly, these motifs share only a 5 base pair core sequence, while the required flanking sequences are distinct for each gene. To determine whether genes other than chemoreceptor genes use similar regulatory mechanisms, I have also defined minimal equences required for the expression of more broadly expressed genes such as odr-4 and kap-1. The LIM homeodomain transcription factor LIM-4 has previously been shown to regulate its own expression in the AWB neurons (Sagasti et al, 1999), and to regulate the expression of all known AWB-specific genes. I am also identifying the sequences in the lim-4 promoter required for autoregulation, and determining whether LIM-4 directly regulates expression of the identified chemoreceptor genes using in vitro and in vivo binding assays. My preliminary data suggest that the cis-regulatory sequences of the studied chemoreceptor gene orthologs in C. briggsae are highly divergent, suggesting independent divergence of chemoreceptor gene regulatory and protein coding sequences. I am also performing forward genetic screens to identify additional trans-acting factors that drive gene expression in the AWB neurons.