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The Xenopus embryo has long served as a
major model for the study of embryonic development because of its
numerous advantages, including external development, large size,
identifiable blastomeres, and its ability to withstand extensive
surgical intervention and culture in vitro. These advantages
enable extensive investigation of the earliest embryonic patterning
events. In fact, much of our current understanding of early embryonic
development derives from experiments performed in the Xenopus
embryo.
The earliest events of all animal embryos are controlled by messenger
RNAs that are deposited in the egg by the mother. These maternal
mRNAs control the embryonic processes that occur prior to the transcription
of the embryonic genome. These processes can best be examined in
Xenopus because, in these embryos, they occur during an especially
long period of time, and because they occur while the embryo is
developing externally. These features have enabled Xenopus
to produce a detailed cellular and molecular understanding of early
patterning events, including a comprehensive view of the role of
specific extracellular growth factors, cell surface receptors, and
intracellular signaling pathway components. These events include
the patterning of the basic body plan, the determination of cell
fate, and the early patterning of major organs, including the digestive
system, circulatory system and nervous system. In addition, many
of the factors originally identified in Xenopus were subsequently
shown to control numerous later developmental events, as well as
other critical biological processes, and oncogenesis. Finally, Xenopus
is a major contributor to our understanding of cell biological and
biochemical processes, including chromosome replication; chromatin,
cytoskeleton, and nuclear assembly; cell cycle progression; and
intracellular signaling. Thus, Xenopus is ideally suited
to provide critical breakthroughs in early embryonic patterning
and cell fate determination, later development and organogenesis,
oncogenesis, and cell biological and biochemical processes.
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