Developmental expression of major myelin protein genes in the CNS of X‐Linked hypomyelinating mutant rumpshaker

Abstract

Rumpshaker (rsh) is an X-linked mutation causing hypomyelination of the CNS of mice and has recently been identified as an allele of jimpy (jp). The mutation (known as jprsh) differs in several respects from other X-linked myelin mutants, including jp, in that mice have normal longevity, oligodendrocyte numbers are not decreased, and cell death is not a feature. Myelin sheaths are deficient in immunostainable PLP protein. The present study examines the developmental expression of the major myelin protein genes and translatability of PLP and MBP mRNA. Differences between the spinal cord and brain of mutants are evident in that mRNA levels are more markedly decreased in the brain. Protein levels are severely reduced in both locations and to a proportionately greater extent than the mRNA, particularly in the spinal cord where PLP RNA and protein are approximately 80% and 10-20%, respectively, of age-matched wild type mice. DM-20 protein, the other major product of the PLP gene, is disproportionately expressed in rumpshaker as is a 10 kDa proteolipid. In vitro translation studies indicate a marked decrease in PLP translation products from mutant RNA. There is no deficiency in the number of PLP mRNA-expressing oligodendrocytes although the abundance per cell is reduced. The data suggest that the phenotypic effects of the mutation may be associated with reduced translation of major myelin proteins, in particular PLP and its incorporation into compact myelin. However, the mutation is compatible with survival of oligodendrocytes and their differentiation to the stage of expressing PLP/DM-20 mRNA.

Late-onset neurodegeneration in mice with increased dosage of the proteolipid protein gene

“…A polyclonal antibody against the common C-terminus (PLP-CT) was used at 1:600 to detect PLP and DM20 (Mitchell et al, 1992). Polyclonal antibodies against myelin basic protein (MBP; Dr. J.-L. Matthieu) and glial fibrillary acidic protein (GFAP; Dako, High Wycombe, United Kingdom) were employed at 1:2,000 and 1:1,000.…”

“…In situ hybridization (ISH) was performed on 8-µm paraffin sections by using an [ 35 S]-labelled riboprobe (PLP-1) recognizing the 5Ј noncoding region and the majority of the open reading frame, which detects both Plp and Dm20 transcripts, as described previously (Griffiths et al, 1989;Mitchell et al, 1992). Following hybridization, the slides were dipped in K5 emulsion, exposed for 2-5 days, developed in D19, air dried, and counterstained with haematoxylin.…”

Phenotypic severity of murinePlp mutants reflects in vivo and in vitro variatioans in transport of PLP isoproteins

“…PLP was stained specifically with a rabbit polyclonal antibody raised against residues 117-129, or with an antibody against the C-terminal hexapeptide common to both PLP and DM20 (PLP-CT) (Mitchell et al, 1992). The PLP-CT antibody was used to identify DM20 in transfected cells and PLP/DM-20 in vivo.…”

“…Any hypothesis must take into account the markedly different phenotypes produced by the these mutations and typified by Plp jp and Plp jp-msd at one end of the spectrum and Plp jp-rsh at the other. The severe phenotype of Plp jp is also associated with the absence of, or very little, PLP and DM20 incorporated into myelin, whereas in Plp jp-rsh , both isoproteins are detectable, although PLP levels are reduced (Mitchell et al, 1992). If a defect in intracellular transport is involved in the pathogenesis, differences should be evident between the oligodendrocyte populations of Plp jp and Plp jp-rsh and between the 2 isoproteins in the Plp jp-rsh mutation.…”

Rumpshaker‐like proteolipid protein (PLP) ratio in a mouse model with unperturbed structural and functional integrity of the myelin sheath and axons in the central nervous system

“…This mutant features a 50% mRNA reduction at p20. In the protein analysis PLP is markedly reduced whereas the intensity of the DM 20 band almost equals that of wt (Mitchell et al, 1992;Schneider et al, 1992). An in- crease in a presumably proteolipid protein related 10 kDa protein and reduced myelin-specific cerebrosides and sulfatides is observed in the rumpshaker mutant mouse Karthigasan et al, 1996).…”