A review of our current knowledge of mesoderm formation in amphibian embryos emphasizes the importance of the transforming growth factor- family of extracellular signalling molecules.
Keywords: Xenopus; embryo; mesoderm; TGF-
Xenopus Embryo: Mesoderm Induction
Leslie Dale, University College London, London, UK
Published online: April 2006
DOI: 10.1038/npg.els.0004189
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Figure 1. Xenopus development. (a) Xenopus early blastula (128 cells) is clearly divided into the darkly pigmented animal hemisphere (top) and the lightly pigmented vegetal hemisphere (bottom). (b) Cross-section through late blastula stage Xenopus embryo showing the large fluid-filled blastocoel (bl) in the animal hemisphere. (c) Vegetal view of early gastrula stage embryo, showing the dorsal blastopore lip. (d) Three-day-old Xenopus tadpole.
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Figure 2. Mesoderm induction. (a) During blastula stages the animal cap is specified as ectoderm, the marginal zone as mesoderm and the vegetal pole as endoderm (left). When the animal cap is grafted on to the vegetal pole (centre), then the animal cap will also form mesoderm (right). The section on the right shows a 3-day-old animal cap that has differentiated a block of muscle (Mu). (b) Mesoderm is also induced in animal cap explants when they are incubated in media containing factors such as Activin (centre). In the absence of these factors the animal cap forms a round ball of epidermis (–), but elongates (+) when incubated in sufficient Activin to induce dorsal mesoderm.
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Figure 3. Three signal model for mesoderm formation. (a) Mesoderm is formed in the marginal zone of blastula stage embryos (left) as a result of two inductive signals. Most vegetal cells (VP) release a signal that induces ventral-type mesoderm (M4), while a small group of cells called the Nieuwkoop centre (N) induce the organizer (O). The organizer differentiates as dorsal mesoderm (M1) and releases signals that both dorsalize the adjacent marginal zone, specifying lateral mesodermal fates (M2 and M3), and induce neural tissue (NT) in the dorsal ectoderm. The remaining ectoderm differentiates as epidermis (Ep), while the vegetal pole differentiates as endoderm (En). (b–c) Whole mount in situ hybridization of early Xenopus gastrulae, viewed from vegetal pole, showing expression patterns of xbra (b) and xgsc (c).
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| Further Reading | |
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