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Fig. 4 Carbaryl-treated embryos have both a decrease in overall number of cardiac precursor cells and delay in cardiac precursor migration. Dorsal views of whole-mount RNA in situ hybridization for cardiac myosin light chain 2 (cmlc2) in MeOH control (A and E) and carbaryl-treated embryos (B–D, F–H) embryos at 20 hpf (A–D) and 30 hpf (E–H). Note the range of phenotypes in carbaryl-treated embryos from reduced endocardial tube fusion (B and C; arrow denotes reduced fusion) to almost complete absence of cmlc2 expression in cardiac field (D). Also note the range of later phenotypes in which ~10% of embryos have an endocardial tube that either has substantial delays in looping or fails to loop (F and G), or loops to the right side (* denotes looping to the right), instead of to the left (H). Scale bars: (A–D) 50 μm; (E–H) 75 μm.