mef2cb morphants displayed defects in early and late myocardial addition. Compared to WT controls (A), 48 hpf mef2cb morphant embryos displayed a heart edema and blood pooling (B). For (C–H) ntl probe was used as a midline reference. mef2cb expression was up-regulated in morphants at 17 hpf (compare C to D) and localization to the posterior ventricle was lost (compare C′′ to D′′). Morphant mef2cb expression at 17 hpf was expended posterior to ntl expression (D), whereas wildtype mef2cb expression is found anterior to ntl expression (C). myl7 expression (E vs. F) and vmhc expression (G vs. H) was reduced in morphants at all stages tested. At 17 hpf, morphant expression of myl7 (F) and vmhc (H) is significantly anterior to ntl expression, whereas wildtype expression of both genes (E and G) is found immediately anterior to ntl expression. At 30 hpf, morphant ventricles were smaller and lacked the late ventricular region (compare I to I′). The in situ data was corroborated by photoconversion assay, in which the morphant ventricle (J′) was smaller compared to controls (J). A decrease in both late and early myocardial addition was observed in mef2cb morphants (K). Data shown as mean ± SEM; **P < 0.01. Scale bar represents 50 μm.
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