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Fig. 1 miR-138 is required for cardiac development. (A) Oblique view of 72 hpf fish after in situ hybridization showing expression of miR-138 in the ventricular chamber marked by blue staining. (B) qRT-PCR analysis of mature miR-138 expression at 48 hpf in flow-sorted cardiomyocytes (cmlc2:GFP), endothelial cells (flk1:GFP), or whole embryos demonstrated enrichment of miR-138 in cardiomyocytes. Mature miR-138 was not detected in endothelial cells. (C and D) Fish embryos injected with miR-138 scrambled control morpholino (scr) (C) or miR-138 morpholino (mo-1) (D) showing pericardial edema (asterisk); arrowhead indicates heart. (E–I) Representative confocal images of transgenic Tg(myl7:HRAS-mEGFP)s843 uninjected embryos (E) or embryos injected with 17-nt miR-138scr (F), 17-nt miR-138mo-1 (G), or a second 31-nt miR-138mo-2 oligo (H). Insets show single z-stack images of outer curvature ventricular myocytes, which normally elongate with maturation (E and F) but remained rounded in the miR-138mo embryos (G and H). (e, eye; y, yolk sac; a, atrium; v, ventricle; avc, atrioventricular canal.)