Figure 2. Islet family members are expressed in distinct patterns in the developing heart.

(a) Confocal images of control and Tg(myl7:EGFP-HsHRAS)^s883isl1−/− embryos or Tg(myl7:EGFP-HsHRAS)^s883 isl1−/− embryos following morpholino-mediated knockdown of Isl2a, Isl2b or Isl2a/Isl2b stained with anti-GFP and anti-Isl1/2 antibodies at 26 hpf. (b) Confocal images of Tg(flk1:EGFP) Isl2a/Isl2b morpholino-injected embryo stained with anti-GFP and anti-Isl1/2 antibodies at 26 hpf. Asterisk indicates the late ventricular region²². White arrows indicate Isl1⁺ cardiomyocytes at the venous pole of the atrium; yellow arrows point to Isl2a⁺ cells in the pericardial wall; yellow arrowheads point to Isl2a⁺ cells in the adjacent endoderm; white arrowheads point to Isl2b⁺ cardiomyocytes at the inner curvature of the ventricle and the outflow pole; blue arrowheads point to Isl1⁺ endothelial cells. Scale bars in (a,b), 50 μm. (c) Schematic representation of the distinct Isl1⁺, Isl2a⁺ and Isl2b⁺ populations at the linear heart tube stage.