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Fig. 5 Differential expression of putative target genes in tbx5a mutants versus tbx5b morphants. A–C: At 36 hours postfertilization (hpf), expression of nppa (a conserved Tbx5 target) was reduced in the atrium of tbx5a mutant embryos, but expressed throughout both chambers in tbx5b morphant embryos, similar to controls. D–F: At 42 hpf, bmp4 was misexpressed throughout the ventricle of homozygous tbx5a mutant embryos. In tbx5b morphant embryos, bmp4 expression was similar to wild-type. G–I: At 42 hpf, soon after looping has begun, wild-type embryos primarily expressed hand2 in the ventricle, but tbx5a mutant and tbx5b morphant embryos showed expanded expression encompassing both chambers. J–L: At 42 hpf, wild-type embryos showed vcana expression restricted to atrioventricular junction (AVJ) boundary, but mutant and morphant embryos showed expanded expression throughout the ventricle and atrium. Arrows, AVJ boundary; arrowheads, sinus venosus. Dotted lines flank the cardiac tissue.