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Fig. 2 Ventral views of the heart in its maximum extension from the anterior to the posterior pole. (A) bmp4 is expressed in the non-chamber myocardium of the heart, the OFT, the AVC and the IFT. (B, C, D) The expression pattern of bmp4 is normal in 42 hpf tbx3b, tbx2a and double morphants. (E) notch1b is expressed in the whole endocardium of the heart tube, but becomes restricted to the endocardium at the level of the OFT and AVC upon looping. (F, G, H) Expression of notch1b is maintained in the endocardium at the level of the chamber myocardium in 48 hpf tbx3b, tbx2a and double morphants, in contrast to wild type. (I) bmp10 is expressed exclusively in chamber myocardium at 42 hpf (J, L, M) In 42 hpf tbx3b and tbx2a morphants bmp10 is expressed in the chamber myocardium and is downregulated in the AVC, as is the case in wild type, but it is not downregulated from the AVC in double morphants. Red arrow indicates the AVC. a, atrium; h, heart; v, ventricle.