Annexin expressions are temporally and spatially regulated during rat hepatocyte differentiation.

Annexin (Anx) 1, 2, 5, and 6 expressions were determined at the transcriptional and translational levels in the rat hepatocytes from gestational day 15 to postnatal day 17. Dramatic shifts were observed in Anx 1 and 2 levels, which peaked at day 1 and gestational day 20, respectively, and reached low levels thereafter. However, Anx 5 and 6 rates were more constant. Prenatal administration of dexamethasone (dex) resulted in a decrease of Anx 1 mRNA levels, and a strong increase in Anx 2 mRNA contents. In adult hepatocytes cultured in the presence of EGF or HGF, Anx 1 and 2 expressions resumed. By immunohistochemistry, Anx 1 was detected only in the cytoplasm of hepatocytes of 1- to 3-day-old rats, Anx 2 and 6 both exhibited a redistribution from the cytoplasm toward the plasma membrane, and Anx 5 was present in the nucleus, cytoplasm, and plasma membrane. Thus, Anx 1, 2, 5, and 6 have individual modes of expression and localization in the differentiating hepatocytes, where they might play unique roles at well defined phases of liver ontogeny.

Increased density of oligodendrocytes in childhood ataxia with diffuse central hypomyelination (CACH) syndrome: neuropathological and biochemical study of two cases.

We report neuropathological, biochemical and molecular studies on two patients with childhood ataxia with diffuse central nervous system hypomyelination (CACH) syndrome, a leukodystrophy recently defined according to clinical and radiological criteria. Both had severe cavitating orthochromatic leukodystrophy without atrophy, predominating in hemispheric white matter, whereas U-fibers, internal capsule, corpus callosum, anterior commissure and cerebellar white matter were relatively spared. The severity of white matter lesions contrasted with the rarity of myelin breakdown products and astroglial and microglial reactions. In the white matter, there was an increase in a homogeneous cell population with the morphological features of oligodendrocytes, in many instances presenting an abundant cytoplasm like myelination glia. These cells were negative for glial fibrillary acidic protein and antibodies PGM1 and MIB1. Some were positive for myelin basic protein, proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein, but the majority were positive for human 2'-3' cyclic nucleotide 3' phosphodiesterase and all were positive for carbonic anhydrase II, confirming that they are oligodendrocytes. Myelin protein and lipid content were reduced. The PLP gene, analyzed in one case, was not mutated or duplicated. The increased number of oligodendrocytes without mitotic activity suggests an intrinsic oligodendroglial defect or an abnormal interaction with axons or other glial cells. This neuropathological study supports the notion that CACH syndrome constitutes a specific entity.

Membrane topology of the myelin/oligodendrocyte glycoprotein.

Myelin/oligodendrocyte glycoprotein (MOG), a specific component of the mammalian central nervous system, is located on the surface of the oligodendrocyte plasma membrane and the outermost lamellae of mature myelin; it is expressed during the latter steps of myelinogenesis. It has been shown that MOG may play a pathological role in autoimmune demyelinating diseases of the central nervous system, although its physiological function remains unknown. MOG is an integral membrane glycoprotein with an extracellular immunoglobulin-like domain and two hydrophobic segments which were predicted to be membrane-spanning on the basis of hydropathy analysis. As a first step in elucidation of MOG function, we have investigated its membrane topology, combining immunofluorescence studies on cultured oligodendrocytes and MOG-transfected Chinese hamster ovary cells with biochemical analyses, including in vitro translation, membrane insertion and protease-digestion assays. Our results indicate that the C-terminal tail of MOG is located into the cytoplasm, and that only the first hydrophobic region of MOG spans the membrane whereas the second hydrophobic region appears to be semi-embedded in the lipid bilayer, lying partially buried in the membrane with its N-terminal and C-terminal boundaries facing the cytoplasm.

Identification of a Val 145 Ile substitution in the human myelin oligodendrocyte glycoprotein: lack of association with multiple sclerosis. The Réseau de Recherche Clinique INSERM sur la Susceptibilité Génétique à la Sclérose en Plaques.

Myelin/oligodendrocyte glycoprotein (MOG) is a major target antigen in experimental autoimmune encephalomyelitis and it has been suggested that it may as well play a key role in the demyelination process in multiple sclerosis (MS). As MOG variants could be pathogenic in autoimmune demyelinating diseases of the central nervous system, we analysed the coding sequence of MOG in MS patients and described a G-->A transition occurring in exon 3 of the human MOG gene. The mutation predicts that isoleucine substitutes for a valine at codon 145 (Val 145 Ile) in the transmembrane region of the protein. This is the first aminoacid substitution reported in human MOG. The polymorphism can be detected by restriction enzyme digestion of genomic DNA or reverse-transcribed PCR amplified products, making it a simple tool to detect a potential implication of MOG alleles in susceptibility to MS by association study. The analysis of 83 unrelated MS patients and 82 unrelated healthy controls showed that the polymorphism is found in similar proportions in MS patients (18%) and controls (14.6%). It is therefore unlikely that the MOG Val 145 Ile variant is responsible for genetic susceptibility to MS.

Structure of the human myelin/oligodendrocyte glycoprotein gene and multiple alternative spliced isoforms.

Myelin/oligodendrocyte glycoprotein (MOG), a specific component of the central nervous system localized on the outermost lamellae of mature myelin, is a member of the immunoglobulin superfamily. We report here the organization of the human MOG gene, which spans approximately 17 kb, and the characterization of six MOG mRNA splicing variants. The intron/exon structure of the human MOG gene confirmed the splicing pattern, supporting the hypothesis that mRNA isoforms could arise by alternative splicing of a single gene. In addition to the eight exons coding for the major. MOG isoform, the human MOG gene also contains, in the 3' region, a previously unknown alternatively spliced coding exon, VIA. Alternative utilization of two acceptor splicing sites for exon VIII could produce two different C-termini. The nucleotide sequences presented here may be a useful tool to study further possible involvement of the MOG gene in hereditary neurological disorders.

Overexpression of annexin V in cystic fibrosis epithelial cells from fetal trachea.

In this report, we investigated the expression of annexins I, II, V, and VI by Northern and Western blot analysis in four cell lines isolated from human fetal tracheae. Two cell lines were obtained from normal fetuses and the two others from fetuses with cystic fibrosis (CF). One CF fetus was heterozygous for the S549N and N1303K substitutions, whereas the other was homozygous for the delta F508 deletion. We found that the four annexins are always coexpressed. The expression of annexins I, II, and VI was the same in the four cell lines. In contrast, that of annexin V was significantly higher in CF than in normal cells. These observations demonstrate that annexins I, II, V, and VI are independently regulated in tracheal epithelial cell lines. Moreover, they suggest that the overexpressed annexin V, a Ca2+ channel, might profoundly modify Ca2+ transport across the membranes of CF cells.

Physical mapping of the human and mouse MOG gene at the distal end of the MHC class Ib region.

Myelin/oligodendrocyte glycoprotein (MOG) is expressed specifically in the central nervous system (CNS) by myelinating glial cells, the oligodendrocytes. The external location of MOG on myelin sheaths and its late expression during myelinogenesis argue for a role of MOG in the completion of myelin and maintenance of its integrity. MOG is a target autoantigen in demyelinating diseases, such as experimental autoimmune encephalomyelitis (EAE) in animals and multiple sclerosis (MS) in humans. We previously located the gene encoding MOG to the major histocompatibility complex (MHC), both in human, by cytogenetics, and in mouse, by analysis of recombinants. To refine the position, we have now selected yeast artificial chromosome clones (YAC) which contain the MOG gene. Physical mapping of the human MOG and the mouse Mog genes by characterization of these YAC clones indicated that the gene is located at the distal end of the major histocompatibility complex (MHC) class Ib region in both species. The human MOG gene lies 60 kilobases (kb) telomeric to HLA-F in a head-to-head orientation; the mouse Mog gene lies 25 (kb) telomeric to H2-M5 in a tail-to-head orientation. These orthologous genes provide markers for comparative analysis of the evolution of the MHC in the two species. The physical mapping of MOG should facilitate analysis of its role in hereditary neurological diseases, and the YAC clones identified here will permit the identification of new genes in the region.

Characterization and expression of the cDNA coding for the human myelin/oligodendrocyte glycoprotein.

We report here the characterization of a full-length cDNA encoding the human myelin/oligodendrocyte glycoprotein (MOG). The sequence of the coding region of the human MOG cDNA is highly homologous to that of other previously cloned mouse, rat, and bovine MOG cDNAs, but the 3' untranslated region differs by an insertion of an Alu sequence between nucleotides 1,590 and 1,924. Accordingly, northern blot analyzes with cDNA probes corresponding to the coding region or the 3' untranslated Alu-containing sequence revealed a single band of 2 kb, rather than the 1.6 kb of bovine, rat, or mouse MOG cDNA(s). Immunocytochemical analysis of HeLa cells transfected with human MOG cDNA, which was performed using a specific antibody raised against whole MOG, clearly indicated that MOG is expressed at the cell surface as an intrinsic protein. These data are in accordance with the predicted amino acid sequence, which contains a signal peptide and two putative transmembrane domains. The knowledge of the human MOG sequence should facilitate further investigations on its potential as a target antigen in autoimmune demyelinating diseases like multiple sclerosis.

Developmental regulation of calmodulin gene expression in rat brain and skeletal muscle.

Three different calmodulin genes that encode the identical protein have been identified in the rat (Nojima, 1989); however, calmodulin gene expression at the various stages of tissue differentiation and maturation has not been previously determined. We have quantitated the content of mRNAs encoding calmodulin in the developing brain and skeletal muscle using RNA blot analysis with three specific cDNA probes. Our results show that five species of calmodulin mRNAs: 4.0 and 1.7 kb for CaM I, 1.4 kb for CaM II, and 2.3 and 0.8 kb for CaM III are detectable at all ages in the brain as well as in skeletal muscle but exhibit a tissue-specific developmental pattern of expression. The comparison of the temporal pattern of calmodulin gene expression with both mitotic activity, as demonstrated by cyclin A mRNA levels, and differentiation and maturation of specific brain or muscle regions is consistent with calmodulin involvement in development.