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November 2000 -- Researchers at Yale have discovered that, contrary to previous beliefs,
the Golgi apparatus is an organelle that exists independently of the
larger endoplasmic reticulum and is a crucial component of cell
Published in a recent issue of Nature, the discovery gives researchers
a better understanding of the cell division process and of the
processes present in the uncontrolled cell division that marks cancer.
In normal cell division, a mother cell divides into two daughters and
the division is regulated until it stops. In a skin melanoma, for
example, the cell division inexplicably starts up again and continues
unregulated. This study could help cancer researchers understand why
the regulation stops.
"Researchers once thought that the Golgi apparatus was no more than an
outgrowth of an organelle called the endoplasmic reticulum," said
Graham Warren, professor of cell biology at Yale and a leading expert
in the field. "We’ve shown that it is an organelle within a cell that
has its own autonomy and so must grow and divide to keep pace with the
growth and division of the cell it inhabits."
The Golgi apparatus sorts and modifies cell products such as hormones,
growth factors and digestive enzymes, and sends them to their final
destinations within the cell. For example, the Golgi decides whether a
given protein will leave the cell or be delivered to the cell surface
or another destination. As with all other cellular organelles, the
Golgi has to grow and divide and has to be inherited.
The Golgi apparatus is normally thought of as a stack of membrane
compartments through which the secretory proteins pass, but Warren and
colleagues have been able to show that the Golgi has an existence even
when these membranes are removed from the apparatus.
"We found that there are proteins, which we term matrix proteins, that
form a scaffold to organize the membranes," said Warren. "We think this
scaffold might be the Golgi apparatus proper, responsible for its
growth, division and partitioning between the two daughter cells."
In past research, Warren and his team have shown that the regrowth of a
mother Golgi in the newly formed daughter cells requires a number of
matrix proteins that are involved in putting the new Golgi complex
The significance of this new finding, Warren said, is at the basic cell
biological level. "People have tended to think of organelles such as
the Golgi in terms of the membranes, in part because this is the
structure you see by electron microscopy," said Warren. "You don't see
the matrix proteins. What we have done is to focus attention on these
underlying structures, which might actually be more relevant to people
interested in studying the biogenesis of these organelles."
Warren said his research brings together a broad spectrum of scientific
disciplines, including traditional cell biology, biochemistry,
molecular biology and structural biology.
"Now that we know that the Golgi is an independent organelle that has
its own identity, we can start looking at it from a basic cell biology
perspective that has medical implications for diseases like cancer, "
Warren’s research team included Joachim Seemann and Marc Pypaert
at Yale and Eija Jokitalo from the Institute of Biotechnology in
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