Figure 1.
Expression of 10J3, a Nodal-regulated gene in endoderm and forerunner cells and regulation by Nodal signaling. Expression of 10J3 (a–e) and sox17 (f) during early embryogenesis. (a,e,f) Dorsal view, animal pole up; (b) lateral view; (c) lateral view; dorsal right; (d) animal pole view, optical section at germ ring level; (f) posterior view, dorsal up. Expression starts at 30% epiboly in a sector of marginal blastomeres (a, arrow) and in the underlying YSL (b, arrow). (c) Until the beginning of gastrulation, both expression domains expand around the margin. (Arrowhead) Start of forerunner cell expression. (d) At the shield stage, expression is detected in hypoblastic endoderm precursor cells (arrows) and in the forerunner cells (not visible). (e) Expression in the endodermal precursors (arrows) and forerunner cells (arrowhead) continues during gastrulation. During the whole gastrulation period, 10J3 and sox17 expression domains within the blastoderm are very similar. (e,f) 70%–80% epiboly. (g–i) 10J3 expression is regulated by the nodal pathway. Embryos are at 60% epiboly. Shown is a dorsal view with the animal pole up. (g) In embryos injected with FastSID mRNA (400 pg), blastodermal 10J3 expression is strongly reduced. (h) Uninjected control embryo. (Arrow) Endodermal precursors. (i) In embryos, injection of Tar* receptor mRNA (1.2 pg), up-regulates and expands cas expression. (j–m) Expression of 10J3 in MZoep embryos. (j,k) Optical section through the marginal region at 30% epiboly. (l,m) Dorsal view at 70% epiboly. (j) 10J3 is expressed only in the YSL in MZoep embryos. (Arrowhead) The limit between the blastoderm and the YSL. (k) In wild-type embryos, expression in marginal blastomeres is observed. (l) At 70% epiboly, cas expression is lost in MZoep embryos, but can be restored ectopically by overexpression of Tar* (m).