Abstract
The paired (prd) gene of Drosophila belongs to the pair-rule class of segmentation genes involved in establishing the metameric organization of the Drosophila body plan. The complex expression pattern of prd has previously been shown to depend upon a number of segmentation genes, including gap and pair-rule genes. In an attempt to characterize and analyze the regulatory regions necessary and sufficient for prd expression, we have identified an 18-kb genomic fragment, consisting of the transcribed portion of prd and 10 kb of 5'- and 5 kb of 3'-flanking region, that is able to rescue prd mutant embryos to full viability. Analysis of a series of prd-lacZ fusion constructs containing progressively reduced lengths of prd 5'-flanking sequences delimits different cis-regulatory regions. The entire 5'-flanking region directs fusion gene expression in a pattern similar, but not identical, to the endogenous prd protein pattern. This 10-kb fragment contains both activator and repressor regions that mediate the establishment of the seven-stripe prd pattern, as well as the splitting into anterior and posterior stripes for the 14-stripe expression phase. The prd intron in combination with a minimal upstream region (0.15 kb) is able to direct low levels of prd-lacZ fusion gene expression in stripes. Information for expression of the anterior dorsal spot and of the early seven-stripe pattern is located downstream of the prd coding region. We propose that regulation of prd by pair-rule and gap gene products is mediated by upstream and downstream cis-regulatory elements. Regulation during separate but overlapping phases of expression by separable regulatory regions might be a general characteristic of segmentation genes.
