The oligodendrocyte-myelin glycoprotein gene is highly expressed during the late stages of myelination in the rat central nervous system.

Oligodendrocyte-myelin glycoprotein (OMgp) is expressed on the surface of oligodendrocytes and neurones and is thought to inhibit axonal regeneration after brain injury in adult, like Nogo and myelin-associated glycoprotein (MAG). We previously observed that the OMgp gene locus on chromosome 17 could be associated with autism, a developmental disorder. The aim of the present study was to characterise the developmental expression of OMgp mRNA in the central nervous system. First we determined the rat OMgp gene sequence and compared it with the human and mouse sequences. Several regions, putative sites for the fixation of transcription factors, are conserved between these three species in the unique intron of this gene. Using quantitative and semi-quantitative RT-PCR, we studied OMgp gene expression in rat brain during post-natal development. We found that OMgp mRNA expression was developmentally regulated, with a peak of expression in the late stages of myelination. We observed a similar profile in oligodendrocyte cultures, in absence of neurones, suggesting that OMgp mRNA expression by oligodendrocytes was independent of axonal influence. Our observations suggest that OMgp is a late marker of myelination, which could be implicated in the arrest of oligodendrocyte proliferation, arrest of myelination or compaction of myelin.

Oligodendrocyte myelin glycoprotein growth inhibition function requires its conserved leucine-rich repeat domain, not its glycosylphosphatidyl-inositol anchor.

The oligodendrocyte myelin glycoprotein (OMgp) inhibits neurite outgrowth and axonal regeneration after brain injury, but its normal function remains unknown. Several observations suggest its implication in cell growth regulation. Here we report an analysis of the domain requirement in OMgp proliferation inhibitory function. We first studied the OMgp protein sequence in 14 mammal species and observed a high conservation of its leucine-rich repeat (LRR) domain. The deletion of this LRR domain is responsible for a total loss of function in an in vitro expression system. The possible three-dimensional structure of the LRR domain of OMgp was modelled using the structure of Yersinia pestis YopM cytotoxin as a template. The predicted arrangement of the LRR segments is compatible with a function of OMgp as a binding protein. The OMgp is a glycosylphosphatidyl-inositol-linked protein anchored in the plasma membrane of oligodendrocytes and neurones. Using deletion mutagenesis, we demonstrated the dispensability of the glycosylphosphatidyl-inositol anchor for OMgp proliferation inhibition function. Our results suggest that OMgp is part of a receptor complex, either as a coreceptor or as a membrane-bound or soluble ligand, involved in the transmission of a growth suppressive signal.

Molecular analysis of the oligodendrocyte myelin glycoprotein gene in autistic disorder.

We previously observed in four autistic patients a new allele (GXAlu 5) of the GXAlu microsatellite marker located in intron 27b of the neurofibromatosis type 1 (NF1) gene (17q11.2). This large intron contains the OMGP gene, coding for the oligodendrocyte myelin glycoprotein expressed by neurons and oligodendrocytes. In the present work, we analysed the distribution of a coding single nucleotide polymorphism (OMGP62) of the OMGP gene, the nearest gene to the GXAlu marker, in a control population (n=101) and in an autistic group (n=65). We observed no significant difference in allele distribution comparing these two groups (chi(2)=1.81; P=0.179). When distinguishing an autistic group with a developmental quotient (DQ) higher than 30 (n=37) and one with a DQ lower than 30 (n=28), we observed an association between allele A and the group with the highest DQ (P=0.015). We found no other polymorphism using SSCP screening and DNA sequencing in the OMGP coding region in 16 autistic patients bearing OMGP62 allele A.

Abnormal SMN1 gene copy number is a susceptibility factor for amyotrophic lateral sclerosis.

The etiology of amyotrophic lateral sclerosis remains unknown in the majority of cases. Homozygous SMN1 (survival motor neuron) gene deletion causes spinal muscular atrophy, and SMN2 gene deletions are possible risk factors in lower motor neuron disease. We studied SMN1 and SMN2 genes copy numbers in 167 amyotrophic lateral sclerosis patients and in 167 matched controls. We noted that 16% of amyotrophic lateral sclerosis patients had an abnormal copy number of the SMN1 gene (1 or 3 copies), compared with 4% of controls. An abnormal SMN1 gene locus may be a susceptibility factor for amyotrophic lateral sclerosis.

Investigation of whole blood and urine monoamines in autism.

Levels of serotonin (5-HT), dopamine (DA), norepinephrine (NE) and epinephrine (E) were determined in the whole blood and urine of 23 children with autism and compared to those of normal children. Very significant group effects (low whole blood 5-HT, high urinary 5-HT and high NE+E in autism) and age effects (urinary 5-HT and DA decrease with age) were found. Moreover, the urinary DA and the whole blood E levels were correlated with clinical findings. The results suggest a maturation defect of noradrenergic systems, possibly disturbed dopaminergic and serotoninergic metabolism, and a functional imbalance among these neurotransmitters in autism.