What is the Cell Cycle?
In order for a living organism to grow their individual cells must
increase
in size, make exact replicas of all their genetic material, and then go
through a process of division. This results in two daughter cells each
with
one complete copy of the genome. The
eukaryotic cell of
a higher organisms, ranging from yeast to humans, has its genetic
material
(DNA) is packaged into a membrane bound nucleus. In eukaryotic cells
the
process of cell growth and division,
the
cell cycle, is
characterized by four distinct phases.
Multicellular organisms, such as humans, contain a vast
number
of cells of many different types and functions. Some of these cells,
e.g.
those lining the stomach and intestine, are continuously replaced by an
actively growing and dividing group of cells. Another group of cells
which is continuously
growing
and dividing are the bone marrow hematopoietic progenitor cells.
Through the process of
hematopoiesis,
these cells proliferate and then differentiate into the separate types
cells
which
circulate in our blood stream: Erythroid progenitors proliferate
rapidly, produce hemoglobin and then expell their nuclei to become red
blood cells, whose major function is to transport oxygen and carbon
dioxide. Myeloid and lymphoid progenitors produce the various lineages
of leukocytes which serve in the defense against infection.
Megakaryocytes produce platelets, cellular fragments which circulate
and initate blod clotting. Other cells, such as liver
hepatocytes,
divide
only rarely but can enter the cell cycle in order to
regenerate
a damaged organ. Still others, such as the neurons of the
brain, cardiac myocytes, and the sensory cells of the retina and
cochlea are terminally differentiated. This means that, although
they are alive and carry out highly specialized functions, they can not
enter the cell cycle, even in the case of tissue injury.
Our laboratory seeks to better understand how the cell cycle control
molecules, the cyclins and their CDK partners, are differentially
regulated
to meet the specialized growth requirements of primary mammalian
cells. In particular we would like to know whether the redundancy
of cell cycle control molecules in vertebrates has facilitated
specialization of cellular growth control. In addition we seek to
determine whether cell cycle gene activation in one cell type leads to
the regulates the proliferation of others through a process of
intracellular communication. By
understanding the pathways of multicellular growth control we hope to
better understand how the process go awry in cancer cells and how we
might be able harness the activity of cell cycle control molecules to
induce regrowth in of post-mitotic tissues.
Fred Hutchinson Cancer Research Center
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