[Neuroscience] Re: Concept of apoptosis
(by jopower At yahoo.com)
Mon Jan 22 16:44:41 EST 2007
I am new to neuroscience, however, hopefully can give
more info on the topic of apoptosis:
The premise is as follows:
PCD or programmed cell death is a genetic program that
gets activated. The idea first came from studies in
c.elegans (most of the work is from Sydney Brenner,
John Sulston and H. Robert Horvitz's labs). C.elegans
is a tranparent free living worm, hermaphrodite and
has very specific (959) number of cells in the adult.
However, when these labs followed the development of
the worm, they found that it had 1090 cells, of which
131 die before reaching adulthood. The location and
the lineage and timing of each of the cells that die
is very precise, and can be followed in each animal.
Ergo: these cells are "programmed to die".
When the genetic pathways were dissected out, it was
found that there were specific genes that are
activated to carry out the "suicide plan". Eg: ced-3
ced-4. A loss of function mutation of these genes
actually reverses the death "pathway" and the worm has
supernumerary cells. They also found another gene that
acted as a "survival gene", where a gain of function
mutation or overexpression actually allowed the cells
to survive (it sort of overrode the program).
That is the basic premise....now to answer your
All these genes are highly conserved, ergo, the PCD
must be a phenomenon across species. In animals where
there are just too many cells, it is a not possible to
clearly demarcate the exact lineage of each cell.
However, it was observed that these cells, (in this
case we speak of neurons..although, PCD occurs in
other cell types and organ systems as well), die
through similar cell death pattern, and activate
similar death program (ergo, the conserved genes are
In case of neuron, the survival signal comes from the
functional synaptic connections that the neuron forms,
mediated through growth factors/integrins/kinase
activation and downstream phosphorylation events etc.
There are cases where either the removal of "survival
signal" or addition of "death signal" can trigger the
After the cell dies, yes, it is cleaned up by
specialized cells like the macrophages or microglia.
hope that answers some of your questions.
--- britches At kittymail.com wrote:
> On question 4 maroon is supposed to be neuron!
> britches At kittymail.com wrote:
> > Hello everyone,
> > I am not sure if this is the best place to ask for
> answers on my
> > questions, but I thought I should consult the
> experts. Recently in a
> > class I asked a few questions and was informed
> that the teacher simply
> > didn't know. These questions are framed from a
> very basic physiology of
> > psychology text.
> > These were my questions about the topic of
> apoptosis, I am refering to
> > the text in them, you can ignore that! Here are
> the questions I had
> > sent to my proffessor:
> > The Carlson text talks about apoptosis. I
> understand that apoptosis is
> > death of a cell due to a chemical signal it
> receives that activates
> > sort of self destruct genetic code inside the
> cell. However I have two
> > questions about this process. In reference to the
> founder cells that
> > help develop the ventricular zone, the text talks
> about them receiving
> > these "chemical signals" that turn on their self
> destruct genes, during
> > the end of the cortical development.
> > QUESTIONS:
> > 1.Where specifically are these chemical signals
> coming from? Where are
> > they created?
> > 2. By what mechanism are they transmitted?
> > 3. How does the creators and transmitors (answers
> to one and 2) know
> > to release them, by what process is this
> > Another area directly relating to the apoptosis
> topic I need some
> > clarification on is that of neuron apoptosis. The
> text states that
> > neurons die by process of apoptosis. However, it
> then goes on to state
> > that neurons migrate and find a space or nitch for
> themselves, when it
> > finds its nitch, the postsynaptic cell creates and
> gives it a signal
> > that LETS it live or tells it to continue living.
> However, when a
> > neuron migrates and finds that a space is already
> taken, it dies. So
> > there is no chemical signal being sent to the
> neuron that dies, it dies
> > from a lack of a signal?
> > QUESTIONS:
> > 4. If the maroon dies because it does not get a
> chemical signal, how is
> > this the same as apoptosis?
> > 5. Does this mean that neurons have an
> automatically set up to destruct
> > and only by chemical permission they then do no
> > 6. The text uses the word "permits" in reference
> to the life giving
> > signal from the postsynaptic cell to the surviving
> neuron, does this
> > then mean that the postsynaptic cell does in fact
> send a chemical to
> > kill any neurons attempting to move into an
> already occupied space?
> > 7. What happens to the expired neuron tissue? Is
> it cleaned? Absorbed?
> > etc.
> > So if anyone can shed some light on any of these
> questions that would
> > be fantastic, or point me in a direction where I
> might find the
> > answers.
> > Thanks for any and all help.
> > -Stacy
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