Comparison of the vein organizing genes abrupt and knirps in the Drosophila wing

This work focused on the formation of the two lateral veins, L2 and L5, formed in similar positions in the posterior and anterior compartments respectively. The position of both veins is determined by the long range morphogen, Dpp. However, each of these veins is formed via a different genetic program that is activated by a specific vein organizing gene: knirps (kni) for L2, and abrupt (ab) for L5. In this study, kni are ab were used to answer an intriguing question: if an ectopic vein organizing gene replaces the correct organizing gene in a vein primordium, how will it affect vein establishment and the genetic program in that location? To address this question, I introduced L2 organizing gene, knirps (kni), or L5 organizing gene, abrupt (ab), into L2 primordium of ri1 mutants, in which L2 vein is missing due to lack of expression of its organizing genes knirps (kni) and knirps -related (knrl). This allowed me to compare the ability of kni and ab to rescue L2 vein in ri1 flies. This was achieved by generating E-kni and E-ab constructs that contain coding region of either kni or ab cloned after L2 enhancer in pHStinger vector. Both constructs were efficient in expressing target gene (kni or ab) in L2 cells of ri1 flies. As it was expected, introduced gene kni was capable to activate L2-specific genetic program and rescue L2 vein in ri1 wing. On the other hand, ectopic expression of ab in ri1 L2 primordium led to disrupted wing phenotypes, in which L2 and L5 vein were erased. It was noticed that the expression of ectopic ab driven by E- ab construct was much stronger than the endogenous level, which resulted stronger and wider expression of key promoting gene rho in L2 and L5 primordial. This could be one of the reasons why L2 and L5 veins were not formed. In addition, ectopic ab was capable to activate only part of L5-specific genetic program that resembled L2 program in principle such as induction of vein marker rhomboid (rho) and repression of intervein gene blister (bs). ab did not trigger part of L5 program that is completely new to L2 primordial cells such as expression of Delta (Dl