Activation of theknirpslocus links patterning to morphogenesis of the second wing vein inDrosophila

Abstract

The adjacent knirps (kni) and knirps-related(knrl) genes encode functionally related zinc finger transcription factors that collaborate to initiate development of the second longitudinal wing vein (L2). kni and knrl are expressed in the third instar larval wing disc in a narrow stripe of cells just anterior to the broad central zone of cells expressing high levels of the related spaltgenes. Here, we identify a 1.4 kb cis-acting enhancer element from the kni locus that faithfully directs gene expression in the L2 primordium. We find that three independent ri alleles have alterations mapping within the L2-enhancer element and show that two of these observed lesions eliminate the ability of the enhancer element to direct gene expression in the L2 primordium. The L2 enhancer can be subdivided into distinct activation and repression domains. The activation domain mediates the combined action of the general wing activator Scalloped and a putative locally provided factor, the activity of which is abrogated by a single nucleotide alteration in the ri53j mutant. We also find that misexpression of genes in L2 that are normally expressed in veins other than L2 results in abnormal L2 development. These experiments provide a mechanistic basis for understanding how kni and knrl link AP patterning to morphogenesis of the L2 vein by orchestrating the expression of a selective subset of vein-promoting genes in the L2 primordium.

Activation and repression activities ofash2inDrosophilawing imaginal discs

“…None of the other possible activators or inhibitors of the L2 enhancer, such as sd, vg or en, showed significant alteration of their expression in ash2 I1 clones (data not shown). Moreover, using a lacZ reporter construct that includes a minimal L2 enhancer element containing only the activator and repressor sites (EX-lacZ) (Lunde et al, 2003), we observed no β-galactosidase expression in ash2 I1 homozygous discs or in mitotic clones (data not shown). Taken together, these results indicate that the ash2-induced repression of kni is independent of sal-C, and suggest that ash2 could be interacting with a kni enhancer other than L2.…”

“…The alleles bs 03267 /CyO (provided by M. Affolter), E(spl)mβ-lacZ (provided by S. Bray) and net 1 were used as intervein markers; the stock w; h kni ri-1 was used to analyse L2 development. To study the effects of ash2 on kni expression, the minimal L2-enhancer element EX-lacZ, a 1.4 kb fragment that contains an activation and repression domain of the kni gene (Lunde et al, 2003) was provided by E. Bier. For ectopic expression of sal-C, we used the UAS-sal 64d transgenic, on the first chromosome, the UAS-salr 8 transgenic, on the second chromosome, and the nubbinGal4 insertion line (provided by J. F. de Celis).…”

Opposing inputs by Hedgehog and Brinker define a stripe ofhairyexpression in theDrosophilaleg imaginal disc

“…The organization of the D-h enhancer is reminiscent of that observed in another recently described enhancer, which is necessary for the development of a specific morphological element of an adult appendage. The knirps (kni) second longitudinal wing vein (L2) enhancer drives expression of kni, which is required to initiate L2 development, in a narrow stripe within the L2 primordia (Lunde et al, 2003). As observed with D-h, localized expression of kn in the L2 primordia is established by an enhancer consisting of discrete activation and repression elements.…”

brinkerandoptomotor-blindact coordinately to initiate development of the L5 wing vein primordium inDrosophila

“…In response to signal X, neighboring cells outside of the sal domain express the L2 vein-organizing genes kni and knrl (Bier, 2000;Lunde et al, 1998). In addition, analysis of an L2-specific cis-regulatory element of the kni/knrl locus provided indirect evidence for negative regulation by a repressor, possibly Brk, expressed in peripheral/lateral regions of the wing disc (Lunde et al, 2003).…”

“…Cells expressing high levels of sal induce expression of knirps (kni) and knirps related (knrl; knirps-like -FlyBase) genes in a narrow stripe of neighboring anterior cells, which express low levels of sal (de Celis and Barrio, 2000;Lunde et al, 1998). Analysis of an L2 veinspecific enhancer element of the kni locus revealed that it consists of an activation domain containing functionally important Scalloped (Sd)-binding sites, as well as a repressor domain containing consensus binding sequences for Sal and Brk (Lunde et al, 2003). Kni/Knrl organize development of the L2 primordium by activating expression of the vein promoting gene rhomboid (rho), as well as by repressing expression of the intervein gene blistered (bs) in the vein primordial cells (Lunde et al, 1998).…”