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. Author manuscript; available in PMC: 2018 Dec 1.
Published in final edited form as: Semin Cell Dev Biol. 2017 Nov 6;72:45–55. doi: 10.1016/j.semcdb.2017.10.033

Figure 2. Specification, Fusion and Differentiation of Muscle Cells.

Figure 2

A) Expression of l’sc occurs in clusters of mesodermal cells with competency to become muscle progenitor cells. B and C) The activity of the Notch and RTK-Ras pathways restricts the expression of l’sc to a single muscle progenitor cell of a particular identity. D) The remaining cells from the initial cluster of promuscle cells become FCMs (pink). The muscle progenitor cells undergo asymmetric division to form either two founder cells (red and purple) or one founder cell (green or yellow) and an adult muscle progenitor (blue). E) Founder cells shown on 2D express different identity genes and undergo several rounds of fusion (actin foci, red) to form syncytial muscle cells with different characteristics. The green founder cell expresses apterous and forms muscle LT1 and the yellow founder cell expresses nautilus to form muscle VA1 (modified from (Dobi et al., 2015)). The myotubes maturate by attaching to tendon cells and developing sarcomeres (not shown). The final position of these muscles is highlighted in the hemisegment schematic on the right.