Fig. 4.

Role of cardiac lb expression in the patterning of the cardiac outflow region. (A and C) Dorsolateral views of 24B-GAL4>UAS-GFP (A) and Tin-GAL4>UAS-GFP (C) embryos showing the GFP-revealed profile of expression driven by these effector lines. Arrows point to the cardiac outflow region. Note the relatively low GFP expression driven in this region by Tin-GAL4. (B) Dorsolateral view of a late stage 14 24B-GAL4>UAS-eve embryo double-stained for Eve and Tin to show that the heart primordium is normally formed in the context of mesodermal Eve misexpression. (D–I) Confocal micrographs showing lateral views of the dorsal part of the embryonic head region. (D, F, G, and I) Stage 15 embryos. (E and H) Stage 14 embryos. (D–I)WT(D–F), (G) heterozygous 24B-Gal4>UASLbe, (H) 24B-GAL4>UAS-Eve, and (I) Tin-GAL4>UASEve embryos stained for myosin heavy chain and Lbe (D, E, G, and H)or β3-tubulin and Lbe (F and I). (D–F)InWT, the main COM branch (open arrowheads) attaches to the second most anterior pair of cardiac cells expressing lb. A separated COM branch (yellow arrowhead in E) displaying weaker level of myosin expression contacts HANCs (filled arrowheads). (G) In embryos with ubiquitous cardiac expression of lbe, COM (open arrowhead) attaches to the tip of the heart and not to the second pair of cardioblasts. COM displays an abnormal shape, and its two branches are difficult to detect. The abnormal contact between COM and the tip of the heart leads to the increased ventral bending of the cardiac outflow region. (H and I) In embryos in which cardiac lb expression was depleted (*), the COM (open arrowheads) extended anteriorly and attached to HANCs (filled arrowheads). (Magnification: A–C, ×200; D–I, ×350.)