Scientists explain difference between fish and men

Embryologists at the University College London have identified one of the key mechanisms in the early stages of embryonic development that differentiates more highly evolved species like humans
from less evolved species like fish. The findings, which shed light on a long-standing scientific puzzle, have been made in the framework of the EU-funded ‘Cells into Organs’ Network of
Excellence.

The project, headed by researcher Claudio Stern and co-funded by the UK-based Biotechnology and Biological Science Research Council (BBSRC), looked into a process known as ‘gastrulation’, which
occurs during week three in human embryonic development. During this process, the mass of undifferentiated cells which an embryo is made of start to arrange themselves into component parts that
eventually form the body. In order to do this, cells group into three layers: the ‘ectoderm’ provides the basis and generates the ‘mesoderm’ and the ‘endoderm’ layers.

In the experimental set-up, the scientists used chicken eggs and an imaging device which displays the three-dimensional movements of cells. They found that, in lower vertebrates, the mesoderm
and the endoderm develop around the edge of the embryo. In higher vertebrates, on the other hand, the two different layers originate from an axis running through the centre of the embryo. The
research also revealed which molecules are responsible for this cell movement. The reason for the position of the axis was that mammals and birds acquire a new mechanism of ‘cell intercalation’
during evolution, the scientists explained.

‘This is an important find as it is a clear difference between the embryonic development of more advanced species and less advanced species,’ said Dr Stern. ‘It suggests that higher vertebrates
must have developed this mechanism later on in the history of animal evolution.’

The Stern group at the University College London is part of the EU’s ‘Cells into Organs’ Network of Excellence, which brings together 25 leading European research groups from Austria, France,
Germany, Italy, the Netherlands, Portugal, the UK and Switzerland. The network receives funding under the EU’s Sixth Framework Programme (FP6).

The network partners are investigating molecular and cellular processes determining the specific development and differentiation of mesodermally derived organ systems, such as the circulatory
systems including the heart, bones, muscles and kidneys. Understanding these processes is essential to developing new therapies in the area of cell and tissue replacement. Such therapies are
considered to be highly promising in the treatment of cancers, but also numerous diseases that affect organ systems.

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