Dissection of the promoter region of the inositol 1,4,5-trisphosphate receptor gene, itr-1, in C-elegans: A molecular basis for cell-specific expression of IP3R isoforms

Inositol 1,4,5-trisphosphate receptors in Caenorhabditis elegans are encode d by a single gene, itr-1. This provides a powerful system in which to diss ect the mechanisms that control the tissue-specific expression of molecules that determine the specificity of calcium signalling We first identified t he Caenorhabditis briggsae orthologue of itr-1, Cbitr-1. Comparison of the two itr-1 genes revealed that the chromosomal organisation, gene structure and predicted cDNA and protein sequences were all conserved. The conserved gene structure supports the hypothesis that the itr-1 gene has three promot ers, each of which gives rise to an alternative mRNA and hence unique prote in. To test this and to identify the roles of the three putative promoters (pA, pB and pC) in regulating itr-2 expression we fused each promoter to th e green fluorescent protein gene and identified their expression patterns, introduction of these transgenes into C. elegans identified unique and defi ned patterns of green fluorescent protein expression directed by each promo ter: pA directs expression in the pharyngeal terminal bulb, the rectal epit helial cells and vulva; pB directs expression in the motor neurone PDA, the amphid socket cells and the spermatheca; pC directs expression in the sper mathecal valve, uterine sheath cells, pharyngeal isthmus and intestine. Thu s tissue-specific expression of itr-1 variants is directed by three promote rs and this results in adjacent cells in the same tissue containing differe nt inositol trisphosphate receptor isoforms. Within pA, four short regions (pA-A to pA-D) of sequence conservation betwe en C. elegans and C. briggsae were identified. Deletion analysis demonstrat ed that the region containing pA-C is required for expression in the termin al bulb and rectal epithelial cells and the region containing pA-D is requi red for expression in the vulva. pA-C includes sequences similar to the bin ding sites for transcription factors that have been demonstrated to be impo rtant in pharyngeal development and gene expression. (C) 2001 Academic Pres s.