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Fig. 5
tbx5 expression in the heart tube. (A,B) In situ hybridization of 26 hfp embryos. (A) At 26 hpf, tbx5 expression is detectable first in the presumptive atrium. (B) Upon longer exposure to substrate, tbx5 expression extends through presumptive atrium and ventricle. Heart tubes of wild-type (shown) and hst mutant embryos (not shown) look identical at this stage. (C,D) In situ hybridization of 48 hfp embryos. (C, wild type; D, hst) tbx5 expression is strongest in the ventricle, and weaker in the atrium. a, atrium; v, ventricle; black arrowhead, venous (atrial) end of heart tube; white arrowhead, arterial (ventricular) end of heart tube.