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Failure of remyelination is largely responsible for sustained neurologic symptoms in multiple sclerosis (MS). MS lesions contain hyaluronan deposits that inhibit oligodendrocyte precursor cell (OPC) maturation. However, the mechanism behind this inhibition is unclear. We report here that Toll-like receptor 2 (TLR2) is expressed by oligodendrocytes and is up-regulated in MS lesions. Pathogenderived TLR2 agonists, but not agonists for other TLRs, inhibit OPC maturation in vitro. Hyaluronan-mediated inhibition of OPC maturation requires TLR2 and MyD88, a TLR2 adaptor molecule. Ablated expression of TLR2 also enhances remyelination in a lysolecithin animal model. Hyaluronidases expressed by OPCs degrade hyaluronan to hyaluronan oligomers, a requirement for hyaluronan/TLR2 signaling. MS lesions contain both [TLR2.sup.+] oligodendrocytes and low-molecular-weight hyaluronan, consistent with their importance to remyelination in MS. We thus have defined a mechanism controlling remyelination failure in MS where hyaluronan is degraded by hyaluronidases into hyaluronan oligomers that block OPC maturation and remyelination through TLR2-MyD88 signaling. hyaluronidase | MyD88 | innate immunity doi/ 10.1073/pnas.1006496107

Experiments are conducted to identify an inherited cerebral neurodegenerative folate transport and metabolism disorder caused by defects in folate receptor alpha due to mutations in the folate receptor1 (FOLR1) gene coding for it. Studies provide information on folate metabolic pathways associated with postnatal myelination, and also prove that folinic acid therapy is effective in treating the disorder and improving brain functions.

The case study of a 3-year old female child manifesting deficiency of aspartate-glutamate carrier isoform 1 (AGC1) that affects psychomotor development is highlighted. The condition was detected as global cerebral hypomyelination and the diagnostic procedure and management of the problem is discussed.

All but the smallest-diameter axons in the central nervous system are myelinated, but the signals that initiate myelination are unknown. Our prior work has shown that integrin signaling forms part of the cell--cell interactions that ensure only those oligodendrocytes contacting axons survive. Here, therefore, we have asked whether integrins regulate the interactions that lead to myelination. Using homologous recombination to insert a single-copy transgene into the hypoxanthine phosphoribosyl transferase (hprt) locus, we find that mice expressing a dominant-negative [beta]1 integrin in myelinating oligodendrocytes require a larger axon diameter to initiate timely myelination. Mice with a conditional deletion of focal adhesion kinase (a signaling molecule activated by integrins) exhibit a similar phenotype. Conversely, transgenic mice expressing dominant-negative 133 integrin in oligodendrocytes display no myelination abnormalities. We conclude that 131 integrin plays a key role in the axoglial interactions that sense axon size and initiate myelination, such that loss of integrin signaling leads to a delay in myelination of small-diameter axons.

Oligodendrocyte precursor cells (OPCs) persist near the demyelinated axons arising in MS but inefficiently differentiate into oligodendrocytes and remyelinate these axons. The pathogenesis of differentiation failure remains elusive. We initially hypothesized that injured axons fail to present Contactin, a positive ligand for the oligodendroglial Notch1 receptor to induce myelination, and thus tracked axoglial Contactin/Notch1 signaling in situ, using immunohistochemistry in brain tissue from MS patients containing chronic demyelinated lesions. Instead, we found that Contactin was saturated on demyelinated axons, Notch1-positive OPCs accumulated in Contactin-positive lesions, and the receptor was engaged, as demonstrated by cleavage to Notch1-intracellular domain (NICD). However, nuclear translocalization of NICD, required for myelinogenesis, was virtually absent in these cells. NICD and related proteins carrying nuclear localization signals were associated with the nuclear transporter Importin but were trapped in the cytoplasm. Abnormal expression of TIP30, a direct inhibitor of Importin, was observed in these OPCs. Overexpression of TIP30 in a rat OPC cell line resulted in cytoplasmic entrapment of NICD and arrest of differentiation upon stimulation with Contactin-Fc. Our results suggest that extracellular inhibitory factors as well as an intrinsic nucleocytoplasmic transport blockade within OPCs may be involved in the pathogenesis of remyelination failure in MS., Introduction Natural remyelination of the central nervous system often occurs spontaneously in various demyelinating diseases, including MS, but only in a subset of patients (1), (2). Oligodendrocyte precursor cells (OPCs) [...]

A large number of cytokines and growth factors support the development and subsequent maintenance of postnatal motor neurons. RegIII[beta] also known as Reg2 in rat and HIP/PAP1 in humans, is a member of a family of growth factors found in many areas of the body and previously shown to play an important role in both the development and regeneration of subsets of motor neurons. It has been suggested that RegIII[beta] expressed by motor neurons is both an obligatory intermediate in the downstream signaling of the leukemia inhibitory factor/ciliary neurotrophic factor (CNTF) family of cytokines, maintaining the integrity of motor neurons during development, as well as a powerful influence on Schwann cell growth during regeneration of the peripheral nerve. Here we report that in mice with a deletion of the Reglll[beta] gene, motor neuron survival was unaffected up to 28 weeks after birth. However, there was no CNTF-mediated rescue of neonatal facial motor neurons after axotomy in KO animals when compared with wild-type. In mice, Reglll[beta] positive motor neurons are concentrated in cranial motor nuclei that are involved in the patterning of swallowing and suckling. We found that suckling was impaired in Reglll[beta] KO mice and correlated this with a significant delay in myelination of the hypoglossal nerve. In summary, we propose that Reglll[beta] has an important role to play in the developmental fine-tuning of neonatal motor behaviors mediating the response to peripherally derived cytokines and growth factors and regulating the myelination of motor axons. Schwann cells | suckling | hypoglossal nerve | LIF

Egr2 is a transcription factor required for peripheral nerve myelination in rodents, and mutations in Egr2 are associated with congenital hypomyelinating neuropathy (CHN) in humans. To further study its role in myelination, we generated mice harboring a hypomorphic Egr2 allele (Egr[2.sup.Lo]) that survive for up to 3 weeks postnatally, a period of active myelination in rodents. These Egr[2.sup.Lo/Lo] mice provided the opportunity to study the molecular effects of Egr2 deficiency on Schwann cell biology, an analysis that was not possible previously, because of the perinatal lethality of Egr2-null mice. Egr[2.sup.Lo/Lo] mice phenocopy CHN, as evidenced by the severe hypomyelination and increased numbers of proliferating Schwann cells of the peripheral nerves. Comparison of sciatic nerve gene expression profiles during development and after crush injury with those of Egr[2.sup.Lo/Lo] Schwann cells revealed that they are developmentally arrested, with down-regulation of myelination-related genes and up-regulation of genes associated with immature and promyelinating Schwann cells. One of the abnormally elevated genes in Egr[2.sup.Lo/Lo] Schwann cells, Sox2, encodes a transcription factor that is crucial for maintenance of neural stem cell pluripotency. 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. The characterization of a mouse model of CHN has provided insight into Schwann cell differentiation and allowed the identification of Sox2 as a negative regulator of myelination.

Proteomic diversity is frequently achieved by alternative RNA-splicing events that can be fine-tuned in tissue-specific and developmentally regulated ways. Understanding this type of genetic regulation is compelling because of the extensive complexity of alternative splicing found in the nervous system, quaking (qk), one of the classical mouse dysmyelination mutants, is defective for the expression of myelin-associated glycoprotein (MAG), and the misregulation of MAG pre-mRNA alternative splicing is implicated as a causal factor. The qk locus encodes several RNA-binding proteins with heterogeneous nuclear ribonucleoprotein K-type homology, a characteristic of several known alternative splicing regulators. Here we test the nuclear-localized qk isoform (QKI-5) for its ability to regulate alternative splicing of MAG pre-mRNA in transient coexpression assays. QKI-5 exhibits properties of a negative regulator of MAG exon 12 alternative splicing. An intronic sequence element required for the repressive function and binding of QKI-5 is also identified. Direct evidence for irregularities in alternative splicing of MAG and other myelin protein transcripts in the qk mouse is demonstrated.

Although knowledge of the functions of neurotrophins has advanced rapidly in recent years, studies concerning the involvement of neurotrophins in glial-neuronal interactions rarely extend further than their roles in supporting the survival and differentiation of neuronal cells. In this study endogenous brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) were identified in Schwann cell/dorsal root ganglia neuronal cocultures and shown to modulate the myelination program of the peripheral nervous system. The differential expression of BDNF and NT3 were examined and compared with the expression profiles of myelin proteins in the cocultures throughout the myelination process. BDNF levels correlated with active myelin formation, whereas NT3 expression was initially high and then down regulated throughout the proliferation and premyelination periods. Addition of exogenous BDNF enhanced myelination, whereas the removal of the endogenous BDNF by using the BDNF receptor TrkB-Fc fusion protein inhibited the formation of mature myelin internodes. Interestingly, exogenous NT3 significantly inhibited myelination, whereas the removal of the endogenous NT3 by using the NT3 receptor TrkC-Fc fusion protein resulted in an enhancement similar to that obtained with the addition of BDNF. In addition, in vivo studies were performed during the development of the mouse sciatic nerve. Subcutaneous injections of BDNF resulted in an enhancement of myelin formation in the sciatic nerve, whereas the removal of the endogenous BDNF dramatically inhibited myelination. Injections of NT3 inhibited myelin formation, and the removal of the endogenous NT3 enhanced myelination. These results demonstrate that BDNF and NT3 possess different modulatory roles in the myelination program of the peripheral nervous system and that their mechanisms of action are specific and highly regulated.

Byline: V. Pingault (1), N. Bondurand (1), C. Le Caignec (1), S. Tardieu (2), N. Lemort (1), O. Dubourg (2), E. Le Guern (2), M. Goossens (1), O. Boespflug-Tanguy (3) Keywords: Key words Sox10; Myelin disorders; Charcot-Marie-Tooth Disease; Pelizaeus-Merzbacher Disease; Leukodystrophy Abstract: The SOX10 transcription factor is involved in development of neural crest derivatives and fate determination in glial cells. SOX10 mutations have been found in patients with intestinal aganglionosis and depigmentation with deafness (Waardenburg-Hirschsprung). Associated neurological signs have been reported in some cases, including a patient exhibiting a central and peripheral myelin deficiency. Therefore, we screened for SOX10 mutations in a large cohort of patients with peripheral and central myelin disorders. 56 were affected by classical demyelinating Charcot-Marie-Tooth disease without identified mutations in the genes encoding PNS myelin proteins (PMP22, P0), connexin 32 and the zinc-finger transcription factor, EGR2. 88 patients with undetermined leukodystrophy were selected from a large European prospective study. Associated clinical, magnetic resonance imaging and electrophysiological signs were consistent with a defect in CNS myelination in 83 and with an active degeneration of the CNS myelin in 5. No abnormalities in the proteolipid protein gene (PLP) were found. The absence of SOX10 mutation in this large cohort of patients suggests that this gene is not frequently involved in peripheral or central inherited myelin disorders. Author Affiliation: (1) Genetique Moleculaire et Physiopathologie INSERM U468 et Laboratoire de Biochimie et Genetique Moleculaire AP-HP, Hopital Henri Mondor, 94 010 Creteil Cedex, France Tel.: +33-149-81-28-61 Fax: +33-149-81-22-19 e-mail: pingault@im3.inserm.fr, FR (2) INSERM U289, Hopital de la Pitie-Salpetriere, Paris, France, FR (3) INSERM U384, Faculte de Medecine, Clermont-Ferrand, France, FR Article note: Received: 24 October 2000, Received in revised form: 7 December 2000, Accepted: 8 January 2001

A GATA-2/estrogen receptor chimera which acts as a ligand-dependent negative self-renewal regulator is discussed. Estrogen and tamoxifen-inducible forms of GATA-2 were used to change levels of GATA-2 in the IL-3-dependent multipotential hematopoietic progenitor cell model FDCP mix and results suggest threshold GATA-2 functions in hematopoietic progenitor cells are critical in determining whether self-renewal or differentiation will occur.

Neuropathological and brain imaging studies suggest that schizophrenia may result from neurodevelopmental defects. Cytoarchitectural studies indicate cellular abnormalities suggestive of a disruption in neuronal connectivity in schizophrenia, particularly in the dorsolateral prefrontal cortex. Yet, the molecular mechanisms underlying these findings remain unclear. To identify molecular substrates associated with schizophrenia, DNA microarray analysis was used to assay gene expression levels in postmortem dorsolateral prefrontal cortex of schizophrenic and control patients. Genes determined to have altered expression levels in schizophrenics relative to controls are involved in a number of biological processes, including synaptic plasticity, neuronal development, neurotransmission, and signal transduction. Most notable was the differential expression of myelination-related genes suggesting a disruption in oligodendrocyte function in schizophrenia.