Fig. 7

tarMR disrupts early endodermal marker expression. Embryos were injected with lacZ RNA (400 pg) as a control or with tarMR RNA (400 pg), fixed at the stage indicated in the lower left corner, and analysed by in situ hybridisation with the marker indicated (upper right). (A, B, animal pole view) gata5 is expressed in the YSL (not visible) and in the blastoderm. Blastodermal expression is lost in (B). (C–F, dorsal view) sox17 labels deep flat endodermal cells and a group of noninvoluting forerunner cells (arrow), which are severely reduced in number in (D) and (F) as compared to controls. (G, H, dorsal view) axial/foxA2 labels the nascent axis and deep scattered endodermal cells (arrowheads). In (H), the axis is unaffected but endodermal cells are missing. At 70% epiboly, tbx6 marks the lateral mesoderm, the precursors of the somites (I). This expression is very partially affected on the dorsolateral side (J). (K–M) The inhibition of endodermal staining of foxA2 by tarMR was rescued by coinjecting with human ALK4.