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Fig. 3
Dorsal marginal enveloping layer cells share characteristics of the dorsal endoderm. A–F. sox17 expression. A,B: Dorsal face views. C–F: Side views. A: 30% epiboly (4.7 h); arrows demarcate a single enveloping cell. B: 70% epiboly (7 h); arrows demarcate a single forerunner cell. C: At 30% epiboly (4.7 h), a cryostat sagittal section showing expression in a single enveloping cell. D‐F: Optical (sagittal) sections on the dorsal axis, (D) 30% epiboly (4.7 h), (E) shield stage (6 h), and (F) 70% epiboly (7 h) showing transition of sox17 expression from dorsal marginal enveloping layer cells to dorsal forerunner cells. Arrow shows expression of surface enveloping layer cells and arrowhead shows unlabeled enveloping layer cells. G–L: Dorsal face views of dorsal forerunner cells at 60% epiboly (6.5 h). ntl (G) and sox17 (J) expression in wild‐type embryos. ntl (H) and sox17 (K) expression in Zoep mutant embryos; and nlt (I) and sox17 (L) expression in MZoep mutant embryos. MZ mutants are shown at lower magnification to show weak expression in the lateral mesendoderm (I) or complete absence of expression (L). Arrows indicate the forerunner cluster or, in the case of its absence, where it should be located.