such as "Introduction", "Conclusion"..etc
Embryologists at UCL (University College London) have helped solve an
evolutionary riddle that has been puzzling scientists for over a
century. They have identified a key mechanism in the initial stages of
an embryo's development that helps differentiate more highly evolved
species, including humans, from less evolved species, such as fish. The
findings of the research, funded by the Biotechnology and Biological
Sciences Research Council (BBSRC), were published online by the journal
Early on in development, the mass of undifferentiated cells that make
up the embryo must take the first steps in deciding how to arrange
themselves into component parts to eventually go on to form a fully
developed body. This is a process known as 'gastrulation'. During this
stage, the cells group into three layers, the first is the 'ectoderm'
which then in turn generates the 'mesoderm' and 'endoderm' layers. In
higher vertebrates, such as mammals and birds, the mesoderm and endoderm
are generated from an axis running through the centre of the embryo.
However, in lower vertebrates, such as amphibians and fish, the two
layers are generated around the edge of the embryo.
Using chicken eggs and a state-of-the-art imaging device which can
reveal how cells move in three dimensions, the researchers demonstrated a
key difference in the way gastrulation occurs between higher vertebrate
species and less evolutionarily advanced animals. They discovered that
the reason why higher vertebrates form their axis at the midline of the
embryo is because during evolution they acquired a new mechanism of
"cell intercalation" which positions the axis at the midline. They also
discovered the molecules used by the embryo to control these cell
Scientists have been speculating for over a century on the difference
between the embryonic development of higher vertebrates and lower
vertebrates, to help answer how the simple cell structure of an embryo
goes on to form the various highly complex bodies of different species.
Research leader Prof Claudio Stern explains: "This is a significant find
as it is a clear difference between the embryonic development of more
advanced species and less advanced species. It suggests that higher
vertebrates must have developed this mechanism later on in the history
of animal evolution.
In humans this process occurs during week 3 of embryonic development,
and forms the cut-off point for scientific research on human embryos in
The research was funded by BBSRC with support from the Medical
Research Council (MRC) and the European Union FP6 Network of Excellence
'Cells into Organs'.
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