We are studying the cellular and developmental functions of C. elegans
ahr-1 and
aha-1 , the orthologs of the mammalian aryl hydrocarbon receptor and ARNT, to better understand the function and regulation of genes containing basic helix-loop-helix and PAS domain motifs. This class of transcriptional regulatory genes has been shown to mediate several important developmental processes in other organisms, including central midline formation, tracheal cell specification, and circadian clock function. The bHLH-PAS proteins function predominantly as heterodimers, and their activities are regulated by nuclear translocation. To analyze the cellular and subcellular localization of AHR-1 and AHA-1, we have generated transgenic lines carrying lacZ and GFP reporters. We have also affinity-purified AHA-1-specific antibodies, and we are in the process of refining the staining conditions. Using our current protocols, the polysera recognizes overexpressed AHA-1-GFP in situ , and we can detect endogenous AHA-1 in some tissues, such as the rectum. AHA-1 is expressed in several cell types that do not express AHR-1-GFP (1), and we hypothesize that AHA-1 has other dimerization partners. By analyzing genomic data, we have identified additional PAS-domain-containing genes, and we are taking two approaches to determine whether they interact with
ahr-1 or
aha-1 . First, we have constructed GFP reporter constructs for these genes and are comparing their expression patterns to those of
aha-1 and
ahr-1 . Second, we have cloned full-length cDNAs, and we will determine which gene products co-immunoprecipitate with AHA-1 in vitro . We have isolated two Tc-1 mediated deletions in the
aha-1 gene, and they are likely null alleles.
aha-1 (
ia01) homozygotes die during early larval development, perhaps due to intestinal tract defects. We are initiating mosaic analysis to better understand the developmental requirements for
aha-1 function. We are also screening for mutations in
ahr-1 . (1) Powell-Coffman, J.A., Jiang, H., Cary, C.L., and Wood, W.B. 1998 Midwest C. elegans Mtg.