Figure 1
From: Distinct genetic programs guide Drosophila circular and longitudinal visceral myoblast fusion
Longitudinal FC migration and fusion lead to the formation of longitudinal visceral muscles. (A–C) Schematic representation of the development of the visceral musculature surrounding the midgut. FCMs have yellow nuclei, and FCs have blue nuclei. Lateral views of the mature visceral muscles around the midgut are shown. (A) At late stage 11, the visceral FCMs are localized in the trunk mesoderm (TCM), circular visceral FCs are organized as a layer adjacent to visceral FCMs, and longitudinal visceral FCs localize in the caudal mesoderm (CVM). (B) Early stage 12 embryo, with binucleated visceral muscles (gray stripes). Many FCMs are localized near the binucleated visceral muscles, and longitudinal spindle-shaped mononucleated FCs are migrating over the layer of visceral circular muscles. (C) Stage 16 embryo with a network of circular and longitudinal visceral muscles. All nuclei of longitudinal visceral muscles express the rP298 enhancer (blue); one nucleus of the circular visceral muscles is rP298 positive (blue), and the other is rP298 negative (brown). (D–I) Embryos with longitudinal FCs expressing HLH54F-lacZ. Nuclei of mesodermal cells in (D, F) were visualized by anti-DMef2 staining. (D) Mononucleated, migrating longitudinal FCs (arrowheads) in early stage 12 embryos. Inset: magnification showing cells contacting each other (arrowhead). (E) Longitudinal FCs (arrowheads) arranged along the stretching, β3Tub-expressing circular muscles (arrow) in stage 12 embryos. (F) Late stage 12 embryo with multinucleated longitudinal FCs. Arrowheads point to nuclei of binucleated and trinucleated cells; arrows indicate cell contacts. (G, H) Stage 14 embryos: at the time when the circular muscles stretched, the multinucleated longitudinal FCs stretched perpendicularly. Arrowheads in (G) point to nuclei of one multinucleated cell; arrowheads in (H) point to cells stretching in anterior–posterior directions. (I) Embryo at the end of development. Longitudinal muscles cover the gut evenly. Arrowheads indicate nuclei of multinucleated muscle. Scale bars: 20 μm.