Further Development 11.7: Play Mix and Match with Vegetal Blastomeres to Prove the Inductive Power of the Nieuwkoop Center

Amphibians and Fish

The Nieuwkoop center was demonstrated in the Xenopus embryo by transplantation and recombination experiments. First, Gimlich and Gerhart (Gimlich and Gerhart 1984; Gimlich 1985, 1986) performed an experiment analogous to the Spemann and Mangold studies, except that they used early Xenopus blastulae rather than newt gastrulae. When they transplanted the dorsalmost vegetal blastomere from one blastula into the ventral vegetal side of another blastula, two embryonic axes formed (Figure 1A). Second, Dale and Slack (1987) recombined single vegetal blastomeres from a 32-cell Xenopus embryo with the uppermost animal tier of a fluorescently labeled embryo of the same stage. The dorsalmost vegetal cell, as expected, induced the animal cap cells to become dorsal mesoderm. The remaining vegetal cells usually induced the animal cap cells to produce either intermediate or ventral mesodermal tissues (Figure 1B). Holowacz and Elinson (1993) found that cortical cytoplasm from the dorsal vegetal cells of the 16-cell Xenopus embryo was able to induce the formation of secondary axes when injected into ventral vegetal cells. Thus, dorsal vegetal cells can induce animal cap cells to become dorsal mesodermal tissue.

Figure 1 Transplantation and recombination experiments on Xenopus embryos demonstrate that the vegetal cells underlying the prospective dorsal blastopore lip region are responsible for initiating gastrulation. (A) Formation of a new gastrulation site and body axis by the transplantation of the dorsalmost vegetal cells of a 64-cell embryo into the ventralmost vegetal region of another embryo. (B) The regional specificity of mesoderm induction demonstrated by recombining blastomeres of 32-cell Xenopus embryos. Animal cap cells were labeled with fluorescent polymers so their descendants could be identified, then combined with individual vegetal blastomeres. The inductions resulting from these recombinations are summarized at the right. D1, the dorsalmost vegetal blastomere, was the most likely to induce the animal cap cells to form dorsal mesoderm. These dorsalmost vegetal cells constitute the Nieuwkoop center.

Literature Cited

Dale, L. and J. M. W. Slack. 1987. Regional specificity within the mesoderm of early embryos of Xenopus laevisDevelopment 100: 279–295.

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Gimlich, R. L. 1985. Cytoplasmic localization and chordamesoderm induction in the frog embryo. J. Embryol. Exp. Morphol. 89: 89–111.

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Gimlich, R. L. 1986. Acquisition of developmental autonomy in the equatorial region of the Xenopus embryo. Dev. Biol. 115: 340–352.

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Gimlich, R. L. and J. C. Gerhart. 1984. Early cellular interactions promote embryonic axis formation in Xenopus laevisDev. Biol. 104: 117–130.

PubMed Link

Holowacz, T. and R. P. Elinson. 1993. Cortical cytoplasm, which induces dorsal axis formation in Xenopus, is inactivated by UV irradiation of the oocyte. Development 119: 277–285.

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