| The present thesis is an investigation into the specification, development and function of the pharyngeal gland cells in C. elegans. Although the role of PHA-4 in the specification of pharyngeal identity has been well established (Gaudet and Mango, 2002; Horner et al., 1998; Kalb et al., 1998; Mango et al., 1994a), little is known about how the cell types within the pharynx are specified. I therefore sought to elucidate the mechanisms responsible for specification of the gland cells. I have thus explored three novel aspects of gland development.;Second, I not only characterize the role of HLH-6 in activating gland gene expression, I also investigate its role in the function of the glands. hlh-6 mutants occasionally arrest as larvae, are slow growing and have small brood sizes suggestive of a defect in the ability of the animals to feed properly. hlh-6 mutants are rescued by feeding on bacteria that are less sticky, suggesting the glands may play a role in lubricating the pharyngeal lumen. In support of this model I show that an HLH-6 dependent gene product is normally found lining the pharyngeal lumen.;Lastly, I identify gland genes whose expression does not require HLH-6. Analysis of two such genes identified a promoter element originally described in the hlh-6 promoter (HRL3 for hlh-6 regulatory element 3) as necessary for HLH-6-independent gland expression. From these studies I propose a model of gland development and compared it to known regulatory networks in the specification of other C. elegans cell types.;The first is the characterization of the only known gland-specific transcription factor. Through bioinformatic analysis, I was able to identify a biologically active cis-regulatory element (called PGM1 for pharyngeal gland motif 1) in the promoters of fourteen gland specific genes. I found that this site is likely a site for the binding of at least two transcription factors and one of those is the gland specific basic-Helix-Loop-Helix transcription factor HLH-6. All PGM1 dependent genes are also HLH-6 dependent, but at least two genes are partially independent of HLH-6 and gland cells are still present in hlh-6 mutants, suggesting HLH-6 does not specify gland fate. |
