Melissa wrote:
>However, the vet believed the likely culprit was a genetic trait causing
>a malformed component of the circulatory system.  He said he'd done some
>research and had seen other, albeit rare, cases of ferrets fitting
>Tasha's general description with such problems.  It seemed to strike
>younger ferrets, about Tasha's age of 2 and a half or so, and those who
>were particularly petite (Tasha never topped 1.5 pounds in her short
>life), and who exhibited certain coloring traits.  The reason for the
>age was that after living a few years, this problem, which was
>degenerative in nature, finally caused the circulatory system to stop
>functioning properly.
 
Yes, he may be talking about a mutation which affects cardiac neural
crest cells; this can also account for high mortality in fetuses and
infants of ferrets with such markings (so can decreased maternal
attention due to not getting the sound signals -- something humans can
work around but other species can't as well.
 
As you know, the earlier an embryo is the more the pliable the cells are,
which is why 5 day old human blastulas (which look like a hollow soccer
ball filled with fluid and have not organs or features or sensory input
of any sort) -- the embryos which are the left over ones after artificial
implantation for fertility that tend to be dumped into the trash in some
places -- are the ones which work best for stem cell research and the
ones under discussion when fetal stem cell lines are mentioned.
 
Okay, over time the cells differentiate into ones which are more
specialized: first a few groups and then more and more so that the cells
become more and more specialized over time.  it's kind of like saying
"Where do you live?  and you answer "America." Okay, which of the
Americas?  Then country, then region, then state, then region or state,
then county, then... More and more specialized so that a large clump
which could have meant many places over time narrows down.  Well, that is
what happens with the cells of a fetus (so now you know why fetal stem
cell lines come from unused blastulas and what happens that allows some
mutations to have variable expression which can be seen widely in many
tissue types.  Now, we already know that the neural crest type of early
cells can become all sorts of things: pigmentation, inner ear structures,
some GI tract aspects, some skull, etc.
 
Before the neural crest cells, though, there is an even more general
grouping which will develop not only into those things but also into the
heart and major blood vessels that supply it.  This grouping is the
cardiac neural crest which later splits into the cardiac crest and the
neural crest.  So, if the mutation affects the cardiac neural crest then
heart or blood vessel defects can also be present.  Mutations to the
cardiac neural crest cells usually (but not always) kill fetus, followed
by infants.  A few live beyond that.  The problems can range from
retaining fetal heart vessels which are needed in the development of
the heart but which prevent effective oxygenation if they are not lost
before birth, to a vessel wrapping the heart, and more.
 
You can see why a mutation which affects the cardiac neural crest cells
can cause some markings to be associated with medical defects of the
heart or its major vessels.
 
Another alternative is aortic defects with strongly non-bilateral head
coloration.  Those go together also for vastly similar reasons, so there
is no reason to repeat myself.  In these individuals the aorta gives out.
I think he is referring to the cardiac neural crest stuff given the size
and age mention.  Aortic Arch mutation individuals aren't as likely to be
stunted and tend to live longer, but of course an individual case can be
very bad.
 
BTW, this week or last (maybe the week before but I don't think so) there
was some very exciting stem cell research with mouse mothers who were
prone to having heart defects in fetuses given stem cell therapy and it
was found that it caused the mothers to secrete a compound that allowed
the fetal hearts to repair themselves before birth, and it not only
worked for pregnancies at the time, but also for later conception.  If
you look in the past posts at Ferret-Genetics in Yahoogroups you will
find the news story link; I carried it to there.
[Posted in FML issue 4669]