Fig. 5. brk induces L5 formation in adjacent omb-expressing cells. Clonal analysis of omb and brk function in L5 development. Adult wings and wing imaginal discs are oriented with the anterior at the top. In adult wings, ventral clones are outlined in blue and dorsal clones are outlined in red. Clones in wing discs are marked by the absence of GFP expression. (A) Wing with an anterior dorsal omb^- clone. The L2 vein extends uninterrupted through the clone. (B) kni expression (red labeling) is normal inside an anterior omb^- mutant clone (arrowhead) in a third instar larval wing imaginal disc. (C) A wing with posterior dorsal omb^- clones. The clone anterior to L5 (arrowhead) does not cause any vein phenotype, whereas the clone that crosses L5 results in vein truncation (arrow). (D) Dl expression (blue labeling) is lost within a posterior omb^- mutant clone (arrowhead) in a third instar larval wing imaginal disc. (E) A wing with a posterior ventral brk^- clone. An ectopic vein runs strictly inside and along the clone border. (F) Dl is ectopically expressed (blue labeling) within and encircling a posterior brk^- clone (arrowhead) in a third instar larval wing imaginal disc. (G) A wing with an anterior ventral brk^- clone. An ectopic vein lies along the border, within the clone (red arrowhead), except near the branch-point with L2 (black arrowhead) where it runs just outside of the clone. (H) kni is ectopically expressed (red labeling) within an anterior brk^- clone (arrowhead) in a third instar larval wing imaginal disc. (I) A wing with overlapping dorsal and ventral posterior omb^- brk^- double mutant clones. Ectopic disorganized veins form within the clone interior. (J) Dl (blue labeling) is expressed within a posterior omb^- brk^- double mutant clone (arrowhead) in a third instar larval wing imaginal disc. Dl is expressed in unorganized pattern, within the interior of the clone. (K) A wing with anterior ventral and dorsal omb^- brk^- double mutant clones. A short segment of vein runs within the interior of the dorsal clone. (L) kni is not misexpressed (red labeling) within anterior omb^- brk^- double mutant clones (arrowheads) in a third instar larval wing imaginal disc. (M) Posterior ventral and dorsal brk^- clones in ab¹/ab¹ mutant flies. The vein running along the posterior clone border is truncated (red arrowhead) in a similar location as the endogenous L5 vein (black arrowhead). In addition, a segment of vein forms within the center of the ventral clone. The phenotypes for the brk^- clones shown in this panel and in E are representative clones scored posterior to or overlapping the L5 vein. Among a total of 44 such brk^- clones generated in a wild-type background, 31 (70%) had veins extending for more than half of the proximal-distal length of the clone. These veins all formed inside and along the clone borders. The remaining 13 brk^- clones had shorter segments of vein, which also ran along and within the clone borders. Among 15 comparably situated brk^- clones generated in an ab^- background, 3 (20%) had veins that extended along more than half the length of the clone border. The remaining clones had only short segments of vein and only 3 (20%) had disorganized vein material forming within the interior of the clone. No such internal disorganized veins were observed in any of the brk^- clones generated in a wild-type background. (N) Ab expression (blue) along the border of a brk^- clone located posterior to L5. No such ectopic Ab expression was observed in brk^- omb^- double mutant clones (O.C., unpublished).