Tail formation as a continuation of gastrulation: the multiple cell populations of the Xenopus tailbud derive from the late blastopore lip
Linda K. Gont, Herbert Steinbeisser, Bruce Blumberg and E. M. De Robertis
Development 119, 991-1004 (1993)
Three lines of evidence suggest that tail formation in Xenopus is a direct continuation of events initiated during gastrulation. First, the expression of two gene markers, Xbra and Xnot2, can be followed from the blastopore lip into distinct cell populations of the developing tailbud. Second, the tip of the tail retains Spemann's tail organizer activity until late stages of development. Third, lineage studies with the tracer DiI indicate that the cells of the late blastopore are fated to form specific tissues of the tailbud, and that intercalation of dorsal cells continues during tail elongation. In particular, the fate map shows that the tip of the tail is a direct descendant of the late dorsal blastopore lip. Thus, the tailbud is not an undifferentiated blastema as previously thought, but rather consists of distinct cell populations which arise during gastrulation.
Overexpression of the homeobox gene Xnot-2 leads to notochord formation in Xenopus
Linda K. Gont, Abraham Fainsod, Sung. H. Kim and Eddy M. De Robertis
Dev. Biol. 174, 174-178 1996
Xnot-2 is a homeobox gene expressed in Spemann's organizer. Here we present evidence that microinjection of synthetic Xnot-2 mRNA leads to the formation of notochord. Microinjection into the dorsal side of the Xenopus embryo results in greatly expanded notochords. Nearby somitic and prechordal mesoderm becomes recruited into these enlarged notochords, which also affect CNS patterning. Two early genes expressed in the developing notochord, chd and XFKH-1, are activated by Xnot-2. We conclude that gain-of-function of Xnot-2 promotes notochord formation.
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