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Fig. 4. AbdA expression and function during cardiac tube remodelling. (A,B) Adult heart stained for AbdA (green), polymerised actin (phalloidin, white) and dMef2 (B, red). AbdA is expressed in segment A5 Tin-expressing myocytes (arrow) and in the posterior-most pair of myocytes that correspond to the anterior-most segment A6 svp-expressing myocytes (arrowhead). (C) Schematic drawing of AbdA expression in the adult cardiac tube. (D-L) In all cases, individuals were shifted to 29°C at the onset of metamorphosis. (D) Posterior tip of a Gal80^ts, 24B>Gal4; dsRNA>abdA; UAS>mcd8-GFP adult cardiac tube, stained for Synaptotagmin (green), GFP (mb GFP, white) and 22C10 (red). 22C10 staining shows that neurones accurately extend to the posterior cardiac tube (red arrows), but abdA loss of function during metamorphosis prevents nerve termination to form synaptic contacts on A5 myocytes, as judged by the absence of sinaptotagmin staining on A5 myocytes (compare with Fig. S2M in the supplementary material). (E,F) Phalloidin staining of the posterior tip of wild-type (E) and Gal80^ts, 24B>Gal4; dsRNA>abdA (F) adult cardiac tubes. Arrows point to Tin-expressing myocytes; arrowheads indicate svp-expressing cells. Loss of abdA function during metamorphosis prevents segment A5 remodelling. Myofibrils are oriented transversally instead of longitudinally and the A5 segment is thicker than in wild type. In F, note that loss of abdA function does not affect histolysis in segments A6-A7. (G,H) Phalloidin staining of a wild-type (G) or Gal80^ts, 24B>Gal4; UAS>abdA (H) adult cardiac tube. In G, magnification of A3-A4 segments illustrates the transversal orientation of myofibrils. (H) The cardiac tube is thinner following AbdA overexpression during metamorphosis and myofibrils are longitudinal, instead of transversal as in the wild type. (I-L) Effects of abdA dosage on Ih expression in the cardiac tube during embryogenesis (I,J) and metamorphosis (K,L). In all cases, anterior is left, Ih transcripts are in green and dMef2 protein in red. Arrows indicate Tin-expressing myocytes, arrowheads svp-expressing myocytes. (I,J) In the embryo, loss of abdA function (I, abd-A^M1) prevents Ih expression in the cardiac tube, whereas abdA misexpression (J, 24B>Gal4; UAS>abdA) induces ectopic expression in Tin-expressing myocytes (red arrows, compare with Fig. 2D). (K) Gal80^ts, 24B>Gal4; dsRNA>abdA adult cardiac tube. Loss of abdA function during metamorphosis induces Ih expression in segment A5 Tin-expressing myocytes (red arrows). (L) Gal80^ts, 24B>Gal4; UAS>abdA adult. abdA overexpression represses Ih transcription in A1-A4 Tin-expressing myocytes (open arrow). Asterisk indicates non-specific fat body staining. Scale bars: 50 µm.

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