Although all mid-blastula cells are pluripotent( Heasman et al., 1984),explants of the animal cap form ectodermal derivatives in culture, while equatorial explants form mesoderm and vegetal explants form endoderm. This mid-blastula embryo has three regions, the animal cap (which forms the roof of the blastocoel), the equatorial or marginal zone (the walls of the blastocoel) and the vegetal mass (the blastocoel floor) (see Fig. The next eleven divisions occur at 20- to 30-minute intervals with no gap phases, while the embryo forms a ball of 4000 cells, which encloses a fluid-filled blastocoel cavity. During the first, 90-minute cell cycle, cortical cytoplasmic movements and male and female pronuclear fusion occur. An overview of early Xenopus developmentĪfter fertilization, Xenopus embryos undergo cell cycles that have characteristic features ( Fig. The question that drives this review is, `What insight have recent functional studies given us on the mechanisms that pattern the early Xenopusembryo?'. For example, the nuts and bolts of development, including the cytoskeletal and adhesion machinery, many components of signaling pathways, transcriptional and cell cycle regulators are incompletely covered. Inevitably, this survey will be incomplete. In this review, I summarize these new findings and incorporate them with the old. The challenge for the modern developmental biologist is to stay abreast of this information. The result is that many more molecules have been shown to control early Xenopus development. The development of loss-of-function technology has also increased our knowledge of individual gene function( Heasman et al., 2000). Over the past 5 years, the usefulness of the Xenopus model organism has grown considerably as a result of the Xenopus Genome Initiative (see This endeavor has provided a quantum increase in the amount of information available on Xenopus genes and the resources with which to study them.
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