regulation of expression from retroviral LTRs

[doug howe]

I have been using a recombinant retroviral vector to express the green 
fluorescent protein in primary cultures of Schwann cells.  I have 
observed a decrease in the intensity of the visible GFP over time, and 
think that it may be related to the rate of proliferation of the cells.  
Does anyone have any information on what may cause a change in expression 
driven by murine leukemia virus LTR?  Any information about what effects 
the persistence or stability of infection by a retrovirus?  

 In addition I wanted to get anyones input on whether or not expression 
from a recombinant retroviral vector was possible prior to its 
integration into the genome,and how long such an event might occur for?

Doug Howe
UNC-Neurobiology