SCO-spondin: a new member of the thrombospondin family secreted by the subcommissural organ is a candidate in the modulation of neuronal aggregation

A number of cues are known to influence neuronal development including growth factors, cell-adhesion molecules, components of the extracellular matrix and guidance molecules. In this study, we present molecular and functional evidence that SCO-spondin, a novel relative of the thrombospondin family, could also be involved in neuronal development by modulating cell aggregative mechanisms. SCO-spondin corresponds to glycoproteins secreted by the subcommissural organ (SCO), an ependymal differentiation of the vertebrate brain located at the entrance to the Sylvian aqueduct. A cDNA clone of 2.6 kb, isolated from a bovine SCO cDNA library, was shown to be specifically and highly expressed in the bovine SCO by in situ hybridization and was subsequently sequenced. Analysis of the deduced amino acid sequence reveals the presence of four conserved domains known as thrombospondin (TSP) type I repeats. To account for the homology with thrombospondins and F-spondin, this secreted glycoprotein was called SCO-spondin. Two potent binding sites to glycosaminoglycan (BBXB) and to cytokine (TXWSXWS) are also found in the TSP type I repeats. The deduced amino acid sequence exhibits three other conserved domains called low density lipoprotein (LDL) receptor type A repeats. The possibility of SCO-spondin involvement in neuronal development as a component of the extracellular matrix is discussed regarding these molecular features. The idea of a modulation of cell-cell and/or cell-matrix interaction is further supported by the anti-aggregative effect observed on cultured neuronal cells of material solubilized from Reissner's fiber. That Reissner's fiber, the condensed secretory product of the SCO present along the whole spinal cord can be a potent morphogenetical structure is an important concept for the analysis of the molecular mechanisms leading to spinal cord differentiation.

Aberrant pre-mRNA maturation is caused by LINE insertions into introns of the white gene of Drosophila melanogaster

Insertional mutagenesis screens have provided thousands of mutant alleles for analysing genes of varied functions in Drosophila melanogaster. We here document mechanisms of insertional mutagenesis by a LINE element, the I factor, by determining the molecular structure of RNAs produced from two alleles of the white gene of D.melanogaster, wIR1 and wIR6. These alleles result from insertion of the I factor into introns of the gene. We show that sequences present within the element direct aberrant splicing and termination events. When the I factor is inserted within the white first intron it may lead to the use of a cryptic 3' splice site which does not contain the dinucleotide AG. This splicing gives rise to a chimeric messenger RNA whose synthesis is controlled differently in tissues where the mutated gene is expressed. When the I factor is inserted within the white last intron it induces synthesis of truncated mRNAs. These results provide, for the first time, mechanisms for I factor insertional mutagenesis. They are discussed in the more general context of RNA processing in Drosophila and the evolution of eukaryotic gene introns.

Reissner's fibre supports the survival of chick cortical neurons in primary mixed cultures

Reissner's fibre, a thread-like structure present in the central canal of the spinal cord, is a product of the condensation of specific glycoproteins that are released by specialized ependymal cells into the cerebrospinal fluid. These secretory ependymocytes constitute the subcommissural organ, a circumventricular organ that lines the roof of the third ventricle of the brain. The subcommissural organ/Reissner's fibre complex is a permanent structure in the vertebrate central nervous system. The addition of bovine Reissner's fibre itself or of soluble material released by Reissner's fibre to primary mixed cultures of chick cerebral cortical cells markedly enhances neuronal survival. The responsive cells have been identified as neurons by labelling them with antibodies to neurofilament proteins. This neuronal survival effect is dose-dependent and does not require the presence of serum in the culture medium. Affinity-purified polyclonal antibodies raised against bovine Reissner's fibre partially block the effect of Reissner's fibre on neuronal survival. These results suggest that Reissner's fibre is involved in developmental processes of the central nervous system.

Dinucleotide repeat polymorphism in the proteolipoprotein (PLP) gene

We report a dinucleotide polymorphism in the first intron of the proteolipid protein (PLP) gene with a heterozygosity frequency of 0.69 useful for molecular analysis of families with X-linked neurologic disorders characterized by dysmyelination of the central nervous system, Pelizaeus-Merzbacher Disease (PMD) and X-linked Spastic Paraplegia (SPG2).

The secretory material of the subcommissural organ of the chick embryo. Characterization of a specific polypeptide by two-dimensional electrophoresis

The subcommissural organ (SCO) is a cerebral gland that releases into the cerebrospinal fluid a carbohydrate-rich glycoprotein which condenses to form Reissner's fiber (RF). Western blots from two-dimensional gel electrophoresis were stained with lectins (Concanavalin-A, wheat germ agglutinin) and anti-bovine RF serum to identify the secretory products of the chick embryo SCO. Immunohistochemical investigations showed that the anti-bovine RF serum reacted exclusively with the secretion of the SCO. Comparative protein patterns of SCO, pineal organ and cerebral hemisphere extracts allowed us to characterize a specific polypeptide in the SCO electrophoretic profiles. The polypeptide was a highly acid compound (isoelectric point of 4.7) with a high molecular weight (390 kDa). On Western blots only this component was immunoreactive with the RF antiserum and it exhibited an affinity for the two lectins. On the basis of these results, this polypeptide may be considered as a specific component of the secretory material synthesized by the SCO cells of the chick embryo.

Specific transcripts analysed by in situ hybridization in the subcommissural organ of bovine embryos

The subcommissural organ (SCO) secretes specific glycoproteins into the cerebrospinal fluid that aggregate to constitute Reissner's fiber (RF), a thread-like structure running along the central canal of the spinal cord. For further identification of the gene(s) encoding these secretions, we have prepared a cDNA library in the vector IGT11 from bovine embryonic SCO. The screening of this library was performed using a polyclonal antibody raised against bovine RF. Three positive clones were isolated and purified and one of these lambda RF101 comprising an insert of #400 nucleotides was undercloned into pBluescript plasmid and mapped. After labeling with 35S (ATP) this cDNA fragment served as a probe to analyse the presence of specific transcripts in the subcommissural organ of the embryonic bovine by in situ hybridization. A labeling signal was observed in the embryonic SCO both in the secretory ependymal and hypendymal cells. This labeling is specific since the ependymal layer bordering the ventricular cavity as well as the surrounding nervous tissue remained negative. Thus, the embryonic SCO contains specific transcripts that are colocalized with the specific glycoproteins as shown after the use of a specific monoclonal antibody C1B8A8. In addition, the pattern of labeling with the specific SCO cDNA is different from those of beta actin cDNA and tear lipocalin cDNA, which, respectively, served as positive and negative controls. In a subsequent set of experiments the expression pattern was compared in embryos at two different stages of development (4-month-old and 8-month-old embryos).(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic homogeneity of Pelizaeus-Merzbacher disease: tight linkage to the proteolipoprotein locus in 16 affected families. PMD Clinical Group

Among the numerous leukodystrophies that have an early onset and no biochemical markers, Pelizaeus-Merzbacher disease (PMD) is one that can be identified using strict clinical criteria and demonstrating an abnormal formation of myelin that is restricted to the CNS in electrophysiological studies and brain magnetic resonance imaging (MRI). In PMD, 12 different base substitutions and one total deletion of the genomic region containing the PLP gene have been reported, but, despite extensive analysis, PLP exon mutations have been found in only 10%-25% of the families analyzed. To test the genetic homogeneity of this disease, we have carried out linkage analysis with polymorphic markers of the PLP genomic region in 16 families selected on strict diagnostic criteria of PMD. We observed a tight linkage of the PMD locus with markers of the PLP gene (cDNA PLP, exon IV polymorphism) and of the Xq22 region (DXS17, DXS94, and DXS287), whereas the markers located more proximally (DXYS1X and DXS3) or distally (DXS11) were not linked to the PMD locus. Multipoint analysis gave a maximal location score for the PMD locus (13.98) and the PLP gene (8.32) in the same interval between DXS94 and DXS287, suggesting that in all families PMD is linked to the PLP locus. Mutations of the extraexonic PLP gene sequences or of another unknown close gene could be involved in PMD. In an attempt to identify molecular defects of this genomic region that are responsible for PMD, these results meant that RFLP analysis could be used to improve genetic counseling for the numerous affected families in which a PLP exon mutation could not be demonstrated.

The Doc transposable element in Drosophila melanogaster and Drosophila simulans: genomic distribution and transcription

The mobile element Doc is similar in structure and coding potential to the LINE families found in various organisms. In this paper, we analyze the insertional and structural polymorphism of this element and show that it appears to have a long evolutionary history in the genome of D. melanogaster. Like the family of I elements, the Doc family seems to display three types of elements: full length elements, defective members that have recently transposed and long since immobilized members common to each D. melanogaster strain. These three classes of Doc elements seem to be present in D. simulans, a closely related species to D. melanogaster. Furthermore, we show that Doc is transcribed as a polyadenylated RNA of about 5 kb in length, presumed to be a full length RNA. This transcript is present in different tissues and at different stages of Drosophila development. These results are compared with previous records on the chromosomal distribution of LINEs or other transposable element families. Doc transcription is analyzed in an attempt to understand the link between Doc transcription and transposition.

Intronic and 5' flanking sequences of the Drosophila beta 3 tubulin gene are essential to confer ecdysone responsiveness

The expression of the beta 3 tubulin gene is regulated, at the transcriptional level, by the steroid hormone ecdysone, in Drosophila Kc cells. Using a transient expression assay, we show that 360 bp from the first intron of the beta 3 tubulin gene, associated with the 5' flanking sequences, are essential to confer ecdysone inducibility on a minimum promoter driving the chloramphenicol acetyl transferase (CAT) gene. The 5' flanking region contains ecdysone-independent cis-positive elements located in proximity to the promoter. Deletion analysis of the 360 bp intronic region reveals that a fragment of 57 bp is crucial for the ecdysone response of the beta 3 tubulin gene. This fragment contains 5'-TGA(A/C)C-3' motifs homologous to ecdysone responsive elements (EcRE) half sites. Band shift assays show that this 57-bp fragment is bound by three specific complexes. One of them appears to be involved in the level of the ecdysone response.

In Drosophila Kc cells 20-OHE induction of the 60C beta3 tubulin gene expression is a primary transcriptional event

In Drosophila Kc cells, the 60C beta3 tubulin transcription unit, whose expression is induced by 20-hydroxyecdysone (20-OHE), has the same structure as in Drosophila. This gene is characterized by an unusual 5' intron of regulating importance, by an alternatively spliced second intron and by a long 3' transcribed but untranslated region. This gene codes for two beta3 tubulin isoforms with one amino acid difference. We have established that beta3 tubulin gene expression is transcriptionally regulated by the steroid hormone in a time and hormonal concentration-dependent fashion, without requirement of protein synthesis. This implies that this transcriptional induction is a primary event and that this gene is probably a direct target for the 20-OHE receptor.

Enhancer and silencer elements within the first intron mediate the transcriptional regulation of the beta 3 tubulin gene by 20-hydroxyecdysone in Drosophila Kc cells

We have studied the transcriptional regulation of the beta 3 tubulin gene by the steroid hormone 20-hydroxyecdysone (20-E) in Drosophila Kc cells. A series of hybrid genes, with different fragments of the beta 3 tubulin gene driving the bacterial chloramphenicol acetyl transferase (CAT) gene were constructed. The promoter activity was assayed after transient expression in Kc cells, in the presence and the absence of 20-E. Constructs with 0.91 kb upstream from the transcription start site and 360 bp from the first large intron allowed the hormonal regulation, i.e. a repression in the absence of 20-E and a derepression-activation in the presence of the hormone. This 360 bp fragment contains several enhancers and silencer(s) sequences. The regulation of the expression of the beta 3 tubulin gene results from the combined activity of all the positive and negative regulatory sequences of the first intron, and a dialogue with the promoter sequences. The nucleotide sequence of this intronic regulatory-fragment has been established and we have identified several EcRE (ecdysone responsive element) consensus sequences.

Presence of the mouse mammary-tumor virus (mmtv) pol gene in breast-cancer

We have used the polymerase chain reaction (PCR) to detect sequences related to the mouse mammary tumor virus (MMTV) reverse transcriptase gene in DNA from breast cancer cell lines and an extensive series of breast tumors. Similar MMTV-related sequences were observed in DNA from normal tissues. The segments amplified by PCR showed over 90% homology to the nucleotide sequence of the MMTV pol gene and no significant differences were noted between the DNA from normal or tumor tissue. When the amplified DNA was used to probe Southern blots, a unique restriction fragment indicative of a single copy locus was detected in all DNAs tested, but the high background of hybridization suggested that many closely related sequences may occur in the human genome.

Screening for new mutations in the LDL receptor gene in seven French familial hypercholesterolemia families by the single strand conformation polymorphism method

To investigate the molecular basis of familial hypercholesterolemia (FH) in France, we applied the single strand conformation polymorphism (SSCP) method to the promoter region and the 18 exons of the low density lipoprotein receptor (LDLR) gene. Seven probands, 4 heterozygotes, 2 compound heterozygotes, and 1 homozygote, belonging to FH families were tested. In all cases, previous genetic analysis and/or LDL receptor fibroblast assay had shown that the disease was due to defects in the LDLR gene. Out of the nine mutations expected, one nonsense mutation in exon 2 and six missense mutations were identified in exons 3, 6, 8, 11, and 15. Two of the latter were found in exon 6. In each family, cosegregation of the base substitution and the disease was observed. Ninety-five control subjects were screened for the presence of the six missense mutations. None was detected, implying that the mutations identified are deleterious. Our results indicate that the SSCP analysis of amplified genomic DNA fragments can be successfully used to rapidly screen mutation containing exons in large genes. Furthermore, all these mutations are newly described and demonstrate heterogeneity of LDLR gene mutations responsible for FH in the French population, as in other reported Caucasian populations.

Detection of Epstein-Barr virus sequences in primary brain lymphoma without immunodeficiency

We searched for Epstein-Barr virus (EBV) sequences by enzymatic DNA amplification in nine primary brain lymphomas from patients without immunodeficiency. We used seven nonlymphoma brain tumors as negative controls, and the Raji cell line as a positive control. We detected EBV DNA, using ethidium bromide-stained-agarose minigel electrophoresis and dot blot hybridization, in the positive control and in only one brain lymphoma tumor; we did not detect EBV DNA in the other tumors. The EBV-positive patient had a second B-cell monoclonal population in the peripheral blood without detectable EBV DNA, suggesting a direct role for EBV in the development of the brain lymphoma.

Clonotypic heterogeneity in cutaneous T-cell lymphomas

The antigen receptor genes studied (immunoglobulin gene for B-cells, and T-cell receptor -beta or -gamma gene for T-cells) represent the most powerful tools for diagnosing the clonality of a lymphoid lineage. We have clonotyped 23 cutaneous T-cell lymphomas and 5 were found to be clonotypically all heterogeneous. Analysis of each patient was performed either from serial skin biopsies taken several months apart or from different tumor samples. In these cases, T-cell lymphoma clonotypic heterogeneity was demonstrated and was especially evident when examining different tumor sites. Moreover, in one case, a biogenotypic population (immunoglobulin and T-cell receptor-rearranged) was found. This unexpected high frequency of T-cell clonal heterogeneity (22%) could be explained either by the evolution of subclones from a single undifferentiated malignant cell or by the independent transformation to cancer of 2 or more lymphocytes, though the latter seems less likely. Clonotypic heterogeneity seems to be as frequent in T-cell lymphomas with cutaneous lesions as in B-cell leukemias.

Regulatory elements in the first intron contribute to transcriptional regulation of the beta 3 tubulin gene by 20-hydroxyecdysone in Drosophila Kc cells

We have studied the transcriptional regulation of the beta 3 tubulin gene by the steroid hormone 20-hydroxyecdysone (20-OH-E) in Drosophila Kc cells. A series of hybrid genes with varying tubulin gene lengths driving the bacterial chloramphenicol acetyl transferase (CAT) gene were constructed. The promoter activity was assayed after transient expression in Kc cells, in the presence or absence of 20-OH-E. We find that 0.91Kb upstream from the transcription start site contain one or several hormone independent positive cis-acting elements, responsible for the constitutive expression of the beta 3 tubulin gene. In the large (4.5 Kb) first intron of this gene, we identified additional hormone dependent negative and positive regulatory elements, which can act in both directions and in a position-independence manner. Then, the negative intron element(s), which repress the transcription in the absence of 20-OH-E has characteristics of silencer.

Detection of Epstein-Barr viral genomes in lymph nodes of Hodgkin's disease patients

Previous studies using Southern blot analysis or in situ hybridization have shown that approximately 20% of patients with Hodgkin's disease have Epstein-Barr virus (EBV) in involved tissues. We used the more sensitive polymerase chain reaction (PCR) technique to determine if a higher percentage of EBV could be detected. Of the 16 Hodgkin's disease patients studied, the PCR technique detected EBV in eight (50%). No prognostic significance was associated with the presence of EBV in the eight EBV-positive patients, and the presence of EBV was not associated with B cell monoclonality.

Dual genotype in cutaneous T-cell lymphomas and pseudolymphomas

Genomic DNA digests of skin biopsies from 20 patients with cutaneous T-cell lymphomas and pseudolymphomas were studied by hybridization, using probes for the constant region of the T-cell receptor beta chain and the joining region of the immunoglobin heavy chain gene. Skin biopsies from all 20 patients contained a monoclonal T-cell population. In addition, DNA from 5 patients contained an immunoglobulin gene rearrangement. These results demonstrate that cutaneous T-cell lymphomas are clonal T-cell malignancies that frequently express a dual genotype, which may sometimes reflect the clonotypic heterogeneity of these disorders.

20-OH-ecdysone regulates 60 C beta tubulin gene expression in Kc cells and during Drosophila development

Cultured Kc cells of Drosophila melanogaster are sensitive to the insect moulting hormone, 20-hydroxy-ecdysone (20-OH-E). Morphological changes of Kc-treated cells were observed and electron microscopic analysis of pseudopodia shows a large increase in the number of microtubules, all arranged in the same orientation. The 60 C beta tubulin gene which is expressed only in 20-OH-E-treated cells encodes a 2.6-kb mRNA which is essentially cytoplasmic and polyadenylated. The corresponding premessenger is 7 kb in length and is absent in untreated cells. Two peaks of expression of the 60 C beta tubulin gene are observed during Drosophila development: at midembryogenesis (stage 8-13 h) and at the late third instar larvae-early pupae stage. By use of the Ecdysone 1 mutant, 60 C beta tubulin gene expression was demonstrated to be regulated in part by 20-OH-E during Drosophila development. Through these two complementary biological models of study, the mode and role of beta tubulin gene regulation are discussed.

[Prenatal diagnosis of X-linked adrenal hypoplasia associated with glycerol kinase deficiency]

We report a case of X-linked adrenal hypoplasia associated with glycerol kinase deficiency in a boy. Cytogenetic studies and X-linked probes did not demonstrate deletion at Xp21. These probes are not informative enough to be used in prenatal diagnosis. This diagnosis was achieved by glycerol concentration assay in amniotic fluid and by maternal plasma estriol assay.

Serum neuron-specific/nonneuronal enolase ratio in the diagnosis of neuroblastomas

Pretreatment samples from 24 children with neuroectodermal tumors (two ganglioneuromas, 22 neuroblastomas) and from 106 others with various tumors were submitted to the enzymatic determination of the serum neuron-specific enolase (NSE). The enzymatic procedure employed in this study allows the systematic determination of the NSE and of the nonneuronal enolase (NNE), thus permitting the calculation of the ratio of the two enolase components. Like results obtained with other procedures, enzymatic determined serum NSE results were raised in a high proportion of Stage IV neuroblastoma (100%) but elevated values also were found in a considerable number of the other tumors (29.2%) like Wilms' tumor, lymphomas, and soft tissue sarcomas. The use of the NSE/NNE ratio which characterizes NSE elevations originating from relative poor or rich sources of NSE, represents an additional index for improving the specificity of the NSE results in the diagnosis of neuroblastomas. With a cutoff value fixed at 7.5%, the specificity of the test is 85.9%. When this limit is fixed at 15%, the specificity reaches 95.3% whereas 81.8% of the results of Stage IV neuroblastomas are still above this value.