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FIG. 1.XHex and cerberus are early markers of the anterior endomesoderm. In situ hybridisation to adjacent serial midsagittal sections of a stage 10ﰂ gastrula embryo. One embryo probed with (A) XHex, cerberus, XSox17b, and Xbra and another embryo probed with (B) XHex, cerberus, chordin, and goosecoid. The dorsal lip is oriented to the bottom left in each. XSox17b marks the future endoderm, Xbra marks the future mesoderm, with chordin and goosecoid marking both prechordal mesoderm and some endodermal cells. A group of cells in the deep organiser expressing XHex, cerberus, goosecoid, and chordin but not XSox17b or Xbra is indicated by the white arrowhead. cerberus-expressing cells at the ventral mesendoderm boundary are indicated by the black arrowhead. The approximate endoderm/ mesoderm boundary based on XSox17ﰀ expression is indicated by the red line. Notice XHex and cerberus are expressed in deep endoderm cells. (C) Cleared whole-mount in situ hybridisation of XHex and cerberus; both embryos are in vegetal view with the dorsal lip uppermost. Note that cerberus is expressed in a broader domain than XHex. (D) In situ hybridisation of XHex and cerberus to sectioned stage 9 blastulae shows that these genes are asymmetrically expressed in the vegetal-equatorial region on one side of the embryo prior to gastrulation. |
