EXPRESSION AND DISTRIBUTION OF CD9 IN MYELIN OF THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS

CD9 is a member of the newly identified tetra-membrane-spanning protei n family. We show here that CD9 is a constituent of myelin in the cent ral and peripheral nervous systems. Expression of CD9 was detected in human cerebral white matter and sciatic nerve by Northern and Western blotting. Myelin in the central and peripheral nervous systems was str ongly stained with a monoclonal antibody against human CD9 antigen in paraffin-embedded sections. CD9 was detected in adult nervous tissue b ut not in developing brain at less than 20 weeks of gestation. Immunoh istochemical studies indicated that expression of CD9 is correlated wi th myelination and is somewhat delayed compared with expression of mye lin basic protein, a major component protein of myelin. br the central nervous system, CD9 was detected along the outermost membrane of comp act myelin but not inside compact myelin or the periaxonal region. Alt hough the membrane-anchored form of heparin-binding epidermal-growth-f actor-like growth factor (proHB-EGF), which is identical to the diphth eria toxin receptor, forms a complex with CD9 in some human and monkey cell lines, proHB-EGF was not detected in myelin immunocytochemically . The distribution of CD9 in the outer surface of myelin aad its relat ively late developmental appearance suggest that CD9 may interact with the extracellular matrix or cell adhesion molecules and participate i n the maintenance of the entire myelin sheath.