EXPANDED CNS MYELIN SHEATHS FORMED IN-SITU IN THE PRESENCE OF AN IGM ANTIGALACTOCEREBROSIDE-PRODUCING HYBRIDOMA

When O1 hybridoma cells, which produce an IgM antigalactocerebroside, are implanted into the dorsal columns of 4-8 d rat spinal cord, some o f the myelin that subsequently develops in the immediate vicinity disp lays an abnormal periodicity. The spacings that are seen cluster at si milar to 19 nm and 31 nm, roughly two and three times the normal 11 nm spacing. In the expanded sheaths, major dense lines are separated by broad extracellular spaces containing a dense material in which single or double rows of similar to 10 nm circular profiles can be identifie d, consistent with the ''central rings'' of IgM molecules. Because IgM is multivalent, it may serve to link adjacent lamellae together in pl ace of intrinsic myelin molecules that normally interact at close rang e. Extensive direct contact between myelin components of successive my elin lamellae is thus not essential to signal the growth of the oligod endrocyte membrane or the spiral wrapping of that membrane around axon s during myelinogenesis, or to stabilize the myelin spiral that forms.