By the use of a rat IgG monoclonal antibody (mab), a mouse mab and human serum containing an IgM mab, all of which react with isolated human myelin-associated glycoprotein (MAG) on immunoblots and bind only to proteins with relative mobilities identical to MAG and dMAG on immunoblots of homogenates of adult human spinal cord, we demonstrated the following: in homogenates of central nervous system tissue from human fetuses of gestational ages that antedate myelination, the anti-MAG antibodies react only with proteins with molecular weights of 250,000 or larger. During myelination the molecular weights of proteins with which the anti-MAG antibodies react shift towards the lower molecular weights found in adult myelin. Amongst those central nervous system regions examined, the shift towards the low molecular weights occurred earliest in the region that is first to become myelinated and latest in the one that is the last to myelinate. Once myelination is completed, the antibodies react only with proteins with relative mobilities identical to those of MAG and dMAG. These developmental changes in molecular weights of "MAG-related proteins" may prove useful as an index of chemical processes on the basis of which myelination occurs.

This content is only available as a PDF.