Figure 2.

SMs were detached in vg^null; rhea¹ embryos but not in SD^3L; rhea¹ embryos. Embryos (stage 16 or a specified stage) are shown as lateral views, with dorsal up, and anterior to the left. Staining is color coded and indicated on each panel. B¹–I¹ are the close-ups of the framed area in B–I. (A) vg is expressed in muscle LL1 and VL1–4. The arrowhead points to a neuronal cell also expressing vg. Compared with wild-type embryos (B), vg^null (C), or rhea¹ single mutation (D), or vg^null; rhea¹ double mutant embryos in early stages (before stage 15; E), all produced a muscle pattern similar to wild-type embryos, except that a vg^null mutation caused muscle VL2 to be missing in ∼30% of segments (star in C¹ and E¹). Notice VL muscles (e.g., VL1) all formed tight adhesions between each other (arrows in B¹–E¹). (F–F¹) By late stage 16 when muscles start to contract, muscle VL1 or other VL muscles detached from the attachment sites only in the vg^null; rhea¹ double mutant embryos (arrows in F¹). Arrows in F indicate detaching muscles and arrowheads indicate detached muscles. (G–H¹) Overview of the vg^null; rhea¹ double mutant embryos (stage 16; G–G^1′) compared with rhea¹ embryos (H–H¹). Both VL1 and VL2 are retracting from their normal attachment sites (arrowhead in G¹–H¹). G¹ and G^1′ are two different confocal sections, and the broken line in G¹ indicates the segment border. (I–I¹) The muscle detachment phenotype of vg^null; rhea¹ embryos can be rescued by expression of Vg via Dmef2-GAL4. Notice VL1 muscles built tight adhesions between each other (arrows in I¹). (J) SD^3L; rhea¹ embryos did not have a muscle detachment phenotype. Some muscles do not develop well (VO4–6; arrowheads) in these embryos, but this mirrors the phenotype seen in SD^3L single mutants.