Activation of the knirps locus links patterning to morphogenesis of the second wing vein in Drosophila
2003
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 spalt
genes. 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 ri 53j 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.
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