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Fig. 2
IRX1b expression in the ventricular chamber of the wild-type embryonic heart. A: Whole-mount in situ hybridization analysis of a wild-type embryo at 53 hours postfertilization (hpf) shows IRX1b expression (blue/purple color) in the ventricle. The atrium is stained by the S46 antibody (brown color), which recognizes an atrial specific myosin heavy chain isoform. B: A section of an IRX1b whole-mount in situ hybridized embryo at 53 hpf, with S46 antibody staining of the atrium, shows a “veil-like” IRX1b expression pattern in the ventricle. C: A sectioned embryo shows IRX1b expression predominantly in the trabeculated spongy myocardium of the ventricle at 53 hpf (blue/purple, arrow). The compact myocardial layer is indicated by an arrowhead. D:IRX1b expressing cells in the ventricle are arranged in a ring structure, as shown by the more intense staining in this section of a whole-mount in situ hybridized embryo at 54 hpf.