Embryonic expression of the soma-restricted products of the myelin proteolipid gene in motor neurons and muscle.

In addition to classic proteolipid protein (PLP) and DM20, the mouse myelin proteolipid gene produces the sr-PLP and sr-DM20 proteins. The sr-isoforms are localized to the cell bodies of both oligodendrocytes and neurons. However, they are expressed to a greater extent in neurons than they are in glia. In this study, we examined expression of the sr-proteolipids in the mouse embryo using immunohistochemistry with an sr-PLP/DM20 specific antibody. Widespread expression of the sr-proteins was found in many nonmyelinating cell types. In particular, strong immunoreactivity was detected in motor neurons of both the autonomic and somatic nervous systems as well as in striated muscle. This pattern of expression persisted throughout the embryonic period studied. Thus, the sr-proteolipids are expressed prior to the onset of myelination and in a much broader array of cell types than their classic counterparts. These results support the conclusion that the sr-isoforms of the PLP gene have a biological role independent of myelination.