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Fig. 2. Left–right axis defects elicited by CA-ALK4 expression. Control and experimental embryos were scored for LR phenotype at day 5 postinjection of CA-ALK4 RNA. The orientation of embryos shown is a ventral view, with anterior at the top. Control embryos exhibit situs solitus, as defined by rightward heart looping (arrowhead) plus counterclockwise coiling and leftward rotation of the gut (A). In contrast, embryos with right-side CA-ALK4 expression exhibit situs inversus, as defined by complete reversal of the heart and gut (B), or situs ambiguus, as defined by reversed heart looping plus normal gut orientation (C) or normal heart looping plus reversed gut orientation (D). The vegetal cell lineages that were targeted for left-side (L3) or right-side (R3) RNA expression are indicated in an illustration of a 16-cell embryo (E, animal pole view). As a control for ALK4 antisense experiments (F), protein levels were examined by Western blot analysis in embryos injected with epitope-tagged ALK4 in the absence and presence of ALK4 morpholino (MO). The ALK4 MO is effective in reducing expression of ectopic ALK4 by approximately 30% when densitometry readings are averaged over the course of three independent experiments. By comparison, levels of a control protein, pinched, are not decreased by co-expressed ALK4 MO. Image published in: Chen Y et al. (2004) Copyright © 2004. Image reproduced with permission of the Publisher, Elsevier B. V. Larger Image Printer Friendly View

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