Disease relevance of Mpz

• In cultures of dissociated cells of embryonic rat DRG, where we knocked-down the C/EBP-delta mRNA, we found an inhibition of P0 mRNA induction by IL6RIL6, showing that the role of C/EBP-delta on this myelin gene is not unique to the melanoma system [1].
• Relapsing lesions, characterized by demyelination of areas previously remyelinated by Schwann cells, were studied for differences in the distribution of P0 and MAG [2].
• Immunocytochemical localization of MAG, MBP and P0 protein in acute and relapsing demyelinating lesions of Theiler's virus infection [2].
• Wild-type Schwann cells infected with Sox2 adenovirus or lentivirus inhibited expression of myelination-associated genes (e.g., myelin protein zero; Mpz), and failed to myelinate axons in vitro, but had an enhanced proliferative response to beta-neuregulin [3].
• Mutations in the human gene for the myelin recognition molecule protein zero (P0) give rise to severe and progressive forms of dominantly inherited peripheral neuropathies [4].

High impact information on Mpz

• These results demonstrate that P0 is essential for the normal spiraling, compaction, and maintenance of the peripheral myelin sheath and the continued integrity of associated axons [5].
• Mouse P0 gene disruption leads to hypomyelination, abnormal expression of recognition molecules, and degeneration of myelin and axons [5].
• In conclusion, P0 and the proteolipid proteins are evolving in parallel in myelinating cells of most vertebrate species [6].
• Vertebrate myelin contains two proteins that mediate compaction: protein zero (P0), an immunoglobulin gene superfamily member, or proteolipid proteins, 4-hydrophobic domain-motif proteins biogenetically unrelated to P0 [6].
• In secondary Schwann cells, both T antigen and c-Jun are required for significant inhibition of the P0 promoter; expression of only one of the proteins is insufficient for repression of the P0 gene [7].

Biological context of Mpz

• To test this directly, we produced mice in which either the MpzS63C (DSS) or MpzS63del (CMT1B) transgene was inserted randomly, so that the endogenous Mpz alleles could compensate for any loss of mutant P0 function [8].
• Analysis of Southern blots of DNA obtained from these hybrids allows us to unambiguously assign the P0 gene to mouse chromosome 1 [9].
• The down-regulation of Pax3, also typical of the transition to myelinating cells, was observed after C/EBP-delta expression in correlation to P0 induction and to decrease of melanogenesis and cell growth [1].
• Similar to the rat gene, the mouse P0 gene is encoded by six exons that span about 7 kb of DNA [10].
• Both cell types appear to influence each other mutually, i.e., impaired T lymphocyte development in RAG-1-deficient P0 mutants leads to decreased macrophage numbers and retarded macrophage activation causes reduced T lymphocyte numbers in the peripheral nerves of P0(+/-) mice [11].

Anatomical context of Mpz

• This observation indicates that mutations in the P0 gene do not account for Trembler, a chromosome 11 mutation that specifically affects myelination in the peripheral nervous system [9].
• We have used somatic cell hybrids to map the gene encoding protein zero (P0), the major structural protein of peripheral myelin [9].
• In search for the molecular mechanisms underlying the formation of the major dense line in peripheral nerve myelin we investigated mice deficient in the myelin proteins P0 and MBP [12].
• At days 12 and 40, the P0 mRNA proportion measured in Trembler sciatic nerves represents only 40% and 7%, respectively, of the proportion measured in control littermates [13].
• In the corresponding double mutants the numbers of macrophages were not elevated in the peripheral nerves, and the demyelinating phenotype was less severe than in the genuine P0+/- mice, demonstrating that macrophages are also functionally involved in the pathogenesis of genetically mediated demyelination [14].

Associations of Mpz with chemical compounds

• Doxycycline-regulated overexpression of C/EBP-delta was sufficient to induce accumulation of P0 and MBP mRNAs, the effect being selective, because C/EBP-delta did not affect several other genes strongly regulated by IL6RIL6 [1].
• By contrast, the concentrations of P0 glycoprotein and myelin basic proteins were reduced to 27% and 20% of control levels, respectively [15].
• The comparison with rat P0 sequence revealed, besides a Lys172 to Arg substitution, that in the first peptide, two serine residues (Ser176 and Ser181) were phosphorylated, Ser176 appearing to be modified subsequently to Ser181 [16].
• In situ hybridization of biotin-labeled P0 rat cDNA probe to chromosome spreads and detection of specific signal with fluorescein isothiocyanate-conjugated avidin revealed a strong signal on the 1(14) translocation chromosome at the site of the breakpoint [17].
• According to the liquid model for interparticle interference from charged spheres, the 80 A-diameter particle has 10 negative surface charges which likely arise from negatively charged SDS molecules bound to the transmembrane domain of P0 [18].

Regulatory relationships of Mpz

• We therefore cross-bred the P0+/- mice with spontaneous osteopetrotic (op) mutants deficient in the macrophage colony-stimulating factor (M-CSF), hence displaying impaired macrophage activation [14].
• We show that MAG-deficient Schwann cells do myelinate DRG neurons in vitro and express the myelin-specific glycolipid galactocerebroside (Gal-C) and the myelin proteins P0 and MBP [19].

Other interactions of Mpz

• In addition to these changes in gene expression in the P0 knockout, PLP/DM-20 accumulates in the endoplasmic reticulum of P0-/- Schwann cells, whereas MAG accumulates in redundant loops of uncompacted myelin, not at nodes of Ranvier or Schmidt-Lantermann incisures [20].
• During formation of myelin sheaths, absence of N-CAM resulted in a transient retardation of Schwann cell spiralling in P0-deficient mice, whereas absence of MAG impaired Schwann cell spiralling for a more extended time period [21].
• In the P0-deficient double mutants also deficient in M-CSF, the numbers of macrophages were not elevated in the demyelinating motor nerves and demyelination was less severe [22].
• Western blots showed that the proteins of compact myelin, P0 glycoprotein, and myelin basic protein were not significantly altered in the mutants; however, the Schwann cell protein, 2',3'-cyclic nucleotide 3'-phosphodiesterase, was reduced to less than half the control level [23].
• The biochemical findings presented in this paper (activity of the enzymes superoxide dismutase, catalase and transglutamase, myelin protein zero expression levels and blood sugar levels) confirm this pathology and exclude other putative pathologies like Amyothrophic Lateral Sclerosis and Hereditary Motor and Sensory Neuropathy [24].

Analytical, diagnostic and therapeutic context of Mpz

• Densitometric analysis of Northern blots showed that, in normal mice, the proportion of P0 mRNA increases up to the 12th day, then decreases slowly [13].
• Using immunological techniques, we show that, as early as postnatal day 8, the P0 content of mice homozygous and heterozygous for the Trembler mutation, represent respectively one tenth and half of the normal values [25].
• Mice heterozygously deficient in the p0 gene (P0(+/-)) are animal models for some forms of inherited neuropathies [22].
• We show that P0 mRNA transcripts are expressed in thymic stroma, similar to other myelin proteins and that expression of intact P0 protein can be detected by Western blot [26].
• DNA sequence conservation within the 5' regions of the human, mouse, and rat P0 genes correlates closely with the results of promoter deletion analysis of the 1.1-kilobase pair region assayed in Schwann cell cultures and reveals a potent proximal region from position -350 to +45 [27].

References