Fig. 3. Segmental differences of the Drosophila cardiac lineages. Stage 15 embryos stained for (A,B) Mef2 (green) and Eve (red), (C,D) Tinman (red) and Eve (green), or Tinman only (E,F). (A) In the wild-type embryos, six myocardial cells and two EPCs are present in each hemisegment from T3 to A7. (B) Overexpression of dap in the mesoderm reduces the myocardial cells from six to four per hemisegment in A2-A7 segments, and in T3-A1 to about three. (C) In wild-type segments A2-A7, four out of six myocardial cells express tinman in each hemisegment; in segment A8, two out of four express tinman; however, in segments T3-A1, all six myocardial cells express tinman. (D) Overexpression of dap in the mesoderm reduces the tinman-expressing myocardial cells in A2-A7 from four to two, in A8 from two to one, and in T3-A1 from six to about three (see insert). (E,F) In CycA or Rca1 mutants, tinman-expressing myocardial cells are reduced from four to two in hemisegments A2-A7, from two to one in A8. However, there is no change in hemisegments T3-A1 in that all six myocardial cells express tinman. Note that the change in myocardial cell number in A2-7 affects heart tube assembly in the posterior abdominal segments, but not in T3-A1 (F).

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