Gata4 mediates the function of Wnt signaling in regulating cardiac laterality. (A-G) Overexpression of gata4 induces lefty2 expression in a spaw-dependent manner. (A,B) Injection of gata4 RNA had no effect on lefty2 expression in floorplate precursors (B), compared with controls (A). Shown are dorsal views of 3-somite staged embryos with anterior to the top. (C-E) Injection of gata4 RNA induced lefty2 expression in diencephalon (D, arrow) and in the right heart field (E, arrowhead). (F,G) Injection of spaw morpholino resulted in a lack of lefty2 expression (F), which cannot be restored by gata4 RNA (G). Shown are dorsal views of 22-somite staged embryos with anterior to the top. (H) Overexpression of gata4 restored lefty2 expression and cardiac looping defects in embryos injected with wnt3 RNA. Shown is the quantification of side-specific gene expression, as well as heart and gut looping. L, left side; A, absence; R, right side; B, bilateral; n, total numbers of embryos scored. (I) Summary of CEI. Correlated expression between spaw and lefty2 was calculated by the co-efficiency index (CEI). Between 17 and 360 embryos were scored for each experimental group.
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