Fig. 3

Hoip regulates somatic muscle and cardioblast maturation but not precursor specification. (A,B) Mef2 and MHC protein expression in St16 embryos. Lateral views. Robust MHC and Mef2 expression is detectable in somatic muscles of hoip¹/Cyo.lacZ embryos (A). Mef2 expression is unaffected in hoip¹ embryos, whereas MHC is nearly absent from the somatic muscle (B). (C-F) St16 rp298.gal4>τ.GFP, rp298.nlacZ embryos double-labeled for GFP (red) and lacZ (green). (C-D2) Dorsal muscles. The number of lacZ⁺ nuclei is reduced in hoip¹ embryos (C) compared with hoip¹/Cyo.lacZ embryos (D); however, binucleated dorsal muscles show complete elongation (arrowheads). (E-F2) Lateral and ventral muscles. The number of lacZ⁺ nuclei is also reduced in lateral and ventral muscles in hoip¹ embryos. Multinucleate lateral muscles show incomplete elongation (arrows). (G,H) Mef2 and MHC protein expression in St16 embryos. Dorsal views. (G) hoip¹/Cyo.lacZ embryos express Mef2 and MHC in mature CBs. (H) hoip¹ embryos express Mef2 but not MHC in a great majority of CBs. (I-L2) Mef2 and Tin protein expression. (I,J) hoip¹/Cyo.lacZ embryos express Mef2 in all myogenic precursors, including CBs. Tin is expressed in four Mef2⁺ CBs per hemisegment at St13 (I; lateral view) and St16 (K; dorsal view). Mef2 and Tin expression in hoip¹ CBs is comparable with control embryos at St13 (J) and St16 (L). (K2,L2) Tin expression alone. (M,N) High magnification micrographs of visceral muscles in St16 embryos. MHC expression is comparable between hoip¹/Cyo.lacZ embryos (M) and hoip¹ embryos (N). Both genotypes develop LVMs and CVMs in the visceral mesoderm. (O) hoip¹ rp298>Hoip embryos express MHC protein at near wild-type levels in the somatic mesoderm. SM, somatic muscle; VM, visceral muscle; LVM, longitudinal visceral muscle; CVM, circular visceral muscle; CBs, cardioblasts. Open arrowheads in I,K show ectodermal cytoplasmic lacZ expression that distinguishes hoip¹ heterozygotes from homozygotes. Scale bars: 20 μm.