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Fig. 2 hand2 overexpression reduces Fn deposition. (A-C) In situ hybridization for myl7. Dorsal views, anterior up. Zebrafish embryos overexpressing hand2 (B) and nat mutant embryos (C) exhibit scattered cardiomyocytes (arrowheads), as well as delayed cardiac fusion. (D-I) Transverse confocal sections of the left lateral mesoderm in embryos expressing Tg(myl7:egfp) (green). Dorsal is up. Immunofluorescence detects ZO-1 (red) and Fn (blue). In contrast to the wild-type monolayer (D), cardiomyocytes are disorganized and multilayered in hand2-overexpressing embryos (E) and nat mutants (F). Furthermore, the deposition of Fn basal to the myocardium (G, arrowheads) is significantly reduced in hand2-overexpressing embryos (H; also see Fig. S2 in the supplementary material) and absent in nat mutants (I). Scale bars: 50 μm in A-C; 10 μm in D-I.