EXPRESSION OF ECOTROPIC MURINE LEUKEMIA-VIRUS IN THE BRAINS OF C58 M,DBA2/J, AND IN UTERO-INFECTED CE/J MICE/

In C58 and AKR mice, endogenous N-tropic, ecotropic murine leukemia vi rus (MuLV) proviruses become activated in rare cells during embryogene sis. Resultant replication competent progeny viruses then actively inf ect a large number of cells throughout the fetus, including cells in t he developing central nervous system. By in situ hybridization analyse s, we have assessed the presence of ecotropic MuLV RNA in the brains o f C58 mice as a function of age. Only a few ecotropic MuLV-positive ce lls were observed in weanling mice, but the number of positive cells i n the brain increased progressively with increasing age of the mice, T hroughout the lives of the mice, the ecotropic MuLV RNA-positive cells were primarily located in well-defined white-matter tracts of the bra in (commissura anterior, corpus callosum, fimbria hippocampi, optical tract, and striatum) and of the spinal cord. Cells of the subventricul ar zone also expressed ecotropic MuLV RNA, and in older mice a small n umber of positive cells were present in the grey matter. Infection of endogenous ecotropic MuLV provirus-less CE/J mice in utero with ecotro pic MuLV clone AKR-623 resulted in the extensive infection of brain ce lls. The regional distribution of ecotropic MuLV RNA-containing cells was the same as observed in the brains of C58 mice, in which cells bec ame infected by endogenously activated virus, but the number of positi ve cells was higher.