The initiation of wing vein development in Drosophila melanogaster

Steroid hormone receptor related transcription factors knirps (kni) and knirps-related (knrl) organize development of the second wing vein (L2), and the glypican dally is required to initiate development of the fifth (L5).;knirps is expressed in the wild-type L2 primordium, but not in radius incompletus (ri) L2 truncation mutants. kni and ri fail to complement when transvection is prevented, and knirps can rescue ri, providing strong evidence for allelism, kni[ ri]. knirps functions downstream of spalt , and upstream of rhomboid. The knirps wing regulatory region, driving expression in L2 and diffusely posterior to that of spalt, lies within a 1.36 kb fragment ∼12 kb upstream of the knirps transcript. In the fragment, kni[ri[1]] has a 252 bp deficiency, within which kni[ri[53j]] has a single base substitution; and kni[ri[M3]] has insertion(s). The 5' half of this fragment has more extensive anterior expression than kni, indicating repression of the 3' half. Substitution of the kni[ri[1]] deficient region into the knirps wing driver abolishes function.;knirps and knrl can each be driven in L2 to rescue kni[ri] mutants. As rhomboid acts downstream of knirps, the ability of rhomboid to rescue kni[ri] suggests that rhomboid is a key target of knirps. Driven in wild-type by the knirps wing regulatory region, araucan causes L2 thinning and Delta results in L2 truncation, indicating that normal development of L2 requires expression of a distinct set of genes.;An EMS screen for viable homozygous wing vein mutants was conducted, and three novel alleles of division abnormally delayed ( dally) were recovered. dally encodes a glypican that may selectively regulate either Dpp or Wingless signaling. The dally mutants have severe L5 truncations, and lack rhomboid expression in the presumptive L5 primordium. Thus, dally is required for L5 initiation. Expression of caupolican and Delta is also lacking in L5 of dally mutants.;dally mutants occasionally have disc duplications, possibly stemming from a role of dally with Wingless during embryonic segmentation or early wing patterning. Those in wing discs become notum-to-wing transformations.