Expression of mesoderm markers in Xenopus laevis Keller explants.

In an attempt to document at the molecular level the behavior of mesodermal cells in Keller explant preparation, we have analyzed the time course of expression of four molecular markers of mesoderm gsc, Xbra, Xnot and XLIM-1. Our findings demonstrate that, (i) all mesodermal markers tested were expressed in the explants, but patterning of the mesoderm appeared incomplete; (ii) during convergence and extension of the explants, mesodermal cells did not invade the ectodermal tissue at any time tested, supporting the view that mesoderm establishes exclusively planar contacts with the ectoderm in this preparation; (iii) planar contacts were not sufficient to promote the neural expression of XLIM-1 protein in these explants.