The jimpy (jp) mutation is a sex-linked disorder which affects myelination in the central nervous system (CNS) of the mouse. A point mutation in the gene coding for the myelin specific proteolipid protein (PLP) has recently been identified. The mutation leads to an altered mRNA for PLP. It has been postulated that the hypomyelination in jp can be attributed either to the absence and/or formation for defective PLP. The critical question which needs to be answered is how this defect affects the biology of the jp oligodendrocyte (OL) and leads to hypomyelination. The present proposal is designed to study whether jp OLs produce any PLP and, if so, how it affects the neurological cells. We will utilize in our studies both the male and the female carrier, with emphasis on the female. The female carrier of the jp gene has a normal lifespan and is an ideal system in which to study the effects of a defective myelin protein upon the biology of the OL partly because the short lifespan of the male prohibits many functional studies. Further, the female is a mosaic and consists of two populations of OLs, one expressing the jp defect and the other the normal phenotype. We will study (1) how normal and abnormal OLs interact in the mosaic, (2) how the normal OLs compensate for the jp OLs, (3) whether defective PLP is made by jp OLs and, if so, how it is processed and (4) if defective PLP is present in jp Schwann cells and how it affects this cell type. With immunocytochemistry, jp and normal Ols in the mosaic will be identified using PLP antibodies specific to normal or jp sequences. The antibodies will also be used on immunoblots to analyze levels of jp PLP in the mosaics at various ages. Structural differences between normal and jp OLs and myelin will be detected with electron microscopy. In situ hybridization studies will also be used to study the different OLs and changes in levels of mRNA during development. Immunocytochemical and morphometric methods will be employed to study mechanisms of compensation in the female. Translation run-off assays and Northern blots will measure levels of PLP synthesis and mRNA in mosaic females. Tissue culture of mosaic brain will be used to study jp OLs and how they interact with normal glia. These studies will answer basic questions regarding the capacity of jp OLs to make PLP and myelin in both mosaic and jp CNS.
