[Neuroscience] Re: Concept of apoptosis

britches At kittymail.com via neur-sci%40net.bio.net (by britches At kittymail.com)
Mon Jan 22 17:06:22 EST 2007


Polly,

Thank you so much for that explnation! It was VERY helpful.

-Stacy

polly jo wrote:
> Hi Stacy,
>
> 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
> questions:
>
> 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
> involved).
>
> 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
> "death pathway".
>
> After the cell dies, yes, it is cleaned up by
> specialized cells like the macrophages or microglia.
>
> hope that answers some of your questions.
>
> best,
> polly
>
>
> --- britches At kittymail.com wrote:
>
> > On question 4 maroon is supposed to be neuron!
> > Sorry!
> >
> > -Stacy
> > 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
> > accomplished?
> > > 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
> > self-destruct?
> > > 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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> >
>
>
>
>
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