Apoptosis - pre-programmed cell death... (2002 Nobel Prize)
Apoptosis, or
programmed cell death, is a normal
cell suicide process in response to cell signals.
It is mediated by a group of gene coded protein-digesting enzymes called
caspases
that in an
ordered series of events dismantles the interior of a cell.
Caspases are a
family of cysteine
proteases, which are activated whenever a cell plans or is signaled to activate
its self-destruction
program. Cell death is characterized by an
overall compaction (shrinking) of the cell & its nucleus,
and the orderly dissection of chromatin by unique endonucleases. Death is
finalized by a rapid
engulfment of the dying cell by phagocytosis of neighboring cells.
Organisms consist of hundreds of cell types, all
originating from a fertilized egg cell. During
development cell numbers increase dramatically, as they form the various tissues
and organs.
Parallel with new cell formations, cell death is a normal process regulating an
appropriate number
of cells in the tissues. Controlled elimination of cells is called
programmed cell death or
apoptosis.
The 2002 Nobel's in Medicine
are for discoveries of the genetic regulation of
programmed cell
death.
The laureates identified key genes regulating organ development and
programmed cell death
&
have shown that corresponding genes exist in higher species, including man. The
discoveries are
important for cancer research via trying to treat disease by turning on
"programmed cell death".
If one can create drugs that may trigger the "self-destruct"
programs to kill off these abnormally
dividing cells cures may be effected.
An example of programmed cell death occurs when
tadpoles undergo tail
metamorphosis to become
adult frogs. In humans inter-digital mesoderm initially formed between fingers
and toes is removed by
programmed cell death.
Sydney Brenner
of the Salk Institute used the
nematode Caenorhabditis
elegans, which became
a multicellular model experimental system, to follow cell division and
differentiation from the
fertilized egg to the adult via microscopic observation. He
demonstrated that a specific gene
mutation, induced by ethyl methane sulfonate, could be linked to a specific
effect in nematode
organ development. His work on nematodes created an experimental system that
laid the foundation
for the study of apoptosis.
John Sulston
of the Wellcome Trust Institute in England
mapped cell lineages, where every cell
division and differentiation could be followed in the development of
C. elegans. There are only
959 cells in an adult nematode. He showed that specific cells lineages
(nerves) undergo programmed
cell death, as an integral part of the normal
differentiation process. He also identified the first
mutation of a gene participating in the cell death process. Sulston also showed
that a protein encoded
by the nuc-1 gene is required for
degradation of the DNA of the dead cell.
Robert Horvitz
of MIT discovered and characterized key
genes controlling cell death in C. elegans.
He identified the first two bona fide "death genes",
ced-3 and ced-4. Functional
ced-3 & ced-4
genes
are a prerequisite for cell death to be executed. Another gene,
ced-9, protects against cell death
by interacting with ced-3 and
ced-4. He has shown how these genes
interact with each other in the
cell death process and that corresponding genes (a
ced-3-like gene) exists in humans.
Some Apoptosis Resources:
J. Kimball's Biology book - apoptosis site
NIH Apoptosis Interest
Group Site
Cell Death
Society
1st Int'l Meeting on Yeast Apoptosis, Oct. 4, 2002
