Transcription results from the combination of multiple factors that act together on a gene's regulatory sequences. To investigate the regulatory logic that can result in cell- specific gene expression, we are studying the expression of the C. elegans
lin-48 gene.
lin-48 is expressed in several cells, including the hindgut, the excretory duct and cells of the head and phasmid. The regulation of this gene in each cell type is distinct. Our work has focused on regulation in the excretory duct cell. Previous experiments identified at least two
lin-48 regulatory regions important for excretory duct cell expression. (Wang and Chamberlin, 2002). The Pax transcription factor EGL-38 was shown to act through one element, whereas the bZip transcription factor CES-2 acts through the other. Since bZip transcription factors can act as either homodimers or heterodimers, we sought to test whether other bZip factors might function with CES-2 to mediate
lin-48 expression in the excretory duct cell. In a yeast two hybrid experiment, the C-terminal region of CES-2 which contains the leucine zipper dimerization domain and DNA binding domain was used as "bait" to screen C. elegans embryonic mRNA library, and four candidate partners were identified. (Metzstein, 1998) We used RNAi to knock down each of these four genes, and found that both K08F8.2 and ZC376.7 affect
lin-48 expression and function in the excretory duct cell. Interestingly, K08F8.2 has two bZip domains and whereas CES-2 and ZC376.7 each have one. Thus, our working hypothesis is that a complex of bZip transcription factors may contribute to the transactivation of
lin-48 in the excretory duct cell. To test this idea, we have carried out in vitro DNA binding assays. We have found that both CES-2 homodimers and a heterodimer of CES-2/K08F2.2 can bind a bZip response element in the
lin-48 sequences. The interaction is mediated between the C-terminal bZip domain of K08F2.2, and not the N-terminal domain. We are testing the possibility that ZC376.7 may interact with the N-terminal bZip domain of K08F8.02, either through another DNA element or as a co-transactivator. Metzstein, (1998) Ph.D thesis. Massachusetts Institute of Technology Wang, X. and Chamberlin, M. H. (2002) Genes and Development 16:2345-2349.