prions

[Ian A. York]

In article <316B77D5.7FEC at pen.gulbenkian.pt>,
Joao Vasconcelos Costa  <jcosta at pen.gulbenkian.pt> wrote:
>
>we accept the prion model, this should mean that the PrP gene is normal-
>ly expressed in those organs. However, I don=B4t remember having ever read
>any paper on the expression of PrP genes in other tissues than the =
>nervous tissues. Does someone know such studies?

Good point.  
  Manson J.  West JD.  Thomson V.  McBride P.  Kaufman MH.  Hope J.
  The prion protein gene: a role in mouse embryogenesis?.
  Development.  115(1):117-22, 1992

"Previous studies have shown that the PrP gene is expressed tissue
specifically in adult animals, the highest levels in the brain, with
intermediate levels in heart and lung and low levels in spleen." 

I didn't find the earlier studies to which they refer, but I didn't look 
very hard.

>Another finding that seems to me difficult to reconcile with the prion
>model is the neuronal pathway of spread of infectivity from the spleen
>to the central nervous system. Any ideas about this?

I've assumed that the spread to the brain is within cells of the 
reticuloenbdothelial system - via monocytes/macrophages.  I suppose it 
could be neuronal as well, or instead (passive axonal transport would 
probably carry the particles to the brain) but it seems simpler to assume 
that they prion is being carried by something to the brain, no?

Ian
-- 
      Ian York   (iayork at panix.com)  <http://www.panix.com/~iayork/>
      "-but as he was a York, I am rather inclined to suppose him a
       very respectable Man." -Jane Austen, The History of England