Expression of extracellular matrix degrading enzymes during migration of xenografted brain cells

Proteolytic enzymes, postulated to create an avenue for cell migration by d igestion of host extracellular matrix molecules, have been implicated in ne oplastic glial cell migration. A similar process is likely to occur in the developing brain, Fetal rabbit brain fragments transplanted into the striat um of the neonatal Shiverer mouse give rise to cells which migrate from the graft site and differentiate into astrocytes and oligodendrocytes. Protein ase expression by transplanted brain cells was studied using immunohistoche mistry and in situ hybridization. Immature donor cells expressed the mRNAs for matrix metalloproteinases (MMP) 1 (collagenase) and 3 (stromelysin), No rthern blot analysis of rabbit brain showed that MMP-1 in particular is exp ressed in the immature rabbit cerebrum and downregulated during maturation. Immature donor cells exhibited immunoreactivity for urokinase plasminogen activator, However, immunoreactivity was also present in maturing neurons. Donor and host astroglia in the vicinity of grafts were immunoreactive for MMP-2 and tissue-type plasminogen activator. This expression may represent a reactive phenomenon, not specifically related to cell migration, by matur e astrocytes, Based upon our findings, MMP-1 appears to be a candidate for involvement in migration of immature brain cells in the cerebrum.