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Fig. 7 The spatial localization of gsc and ntl transcripts in b-galactosidase-RNA-injected and wnt8-RNA-injected embryos at 55-60% epiboly. Embryos in A, C, E and G are oriented animal pole to the top, whereas embryos in B, D, F and H are viewed from the animal pole. (A,B) gsc expression in embryos injected with 1 ng of b-galactosidase RNA. gsc expression is restricted to the shield (arrow) in these embryos. (C,D) gsc expression in embryos injected with approximately 0.5 ng of wnt8 RNA. Note that the gsc signal has expanded in thickness at the germ ring (arrows) and there is no readily identifiable shield. The increased gsc signal in the germ ring can occur in a uniform manner around the entire circumference as in C, or as seen in a view from the animal pole of another early gastrula embryo (D), it may appear intermittently in a random fashion (arrows). (E,F) The spatial pattern of ntl expression in embryos injected with approximately 1 ng of b- galactosidase RNA. The ntl signals are detected in the germ ring (arrows) and in cells that have involuted in the embryonic shield (open arrow). (G,H) The spatial pattern of ntl expression in embryos injected with approximately 0.5 ng of wnt8 RNA, illustrating the increase in the width of the ntl expression in the germ ring (arrows). In addition, the ntl signal in cells ventral to the germ ring in the enveloping layer (open arrows), has increased over those cells in b- galactosidase injected (F) or uninjected controls (data not shown). This apparent increase in the signal is not restricted to any one region since there are numerous cells around the entire germ ring expressing ntl (open arrows, H). Scale bar (A-H), 65 μm.