PubMed Health⌕ Search

Biomedical subjects

N Benachenhou

Publications and source records attributed to N Benachenhou.

10 recordsLinked to original sources
PubMed2001

Physical and transcriptional map of the mouse Chromosome 10 proximal region syntenic to human 6q16-q21.

Toward the isolation of the grey-lethal (gl) gene, we have genetically localized this locus on mouse Chromosome (Chr) 10 between the Fyn gene and the D10Mit148 microsatellite marker. Here, we have screened five yeast artificial chromosome (YAC) libraries and isolated more than 100 YAC clones mapping to this region. Forty-two clones were characterized and assembled in an approximately 8.5 megabases (Mb) contig showing high linkage conservation with the human 6q16-q21 interval. During this study, 24 specific novel sequence-tagged sites (STSs) were derived from YAC insert ends, and 15 mouse genes were precisely mapped to the contig. The physical and transcriptional map presented here will provide novel resources to isolate the gl locus associated with osteopetrosis, and will also provide candidate loci for other defects mapped on human Chr 6q.

Animals↗
PubMed2001

The mouse osteopetrotic grey-lethal mutation induces a defect in osteoclast maturation/function.

The osteopetrotic grey-lethal (gl) mouse mutant displays many similarities to the human malignant autosomal-recessive form of osteopetrosis. In this study, we show that the gl osteopetrotic bone phenotype is characterized by the presence of numerous differentiated multinucleated osteoclasts. A significant increase in the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts was detected in vivo, suggesting induction of differentiation in the osteoclast lineage as a compensatory mechanism. These gl osteoclast cells demonstrated a defective cytoskeletal reorganization and an underdeveloped ruffled border, a membrane structure essential for active bone resorption. Accordingly, resorption activity of these cells is markedly impaired by four- to tenfold as evaluated with the pit formation assay. This low bone resorption in gl osteoclasts is highly reminiscent of the loss in key enzymes, V-ATPase or cathepsin-K, and in signaling factors, Src or TRAF-6, which were shown not to be significantly altered in gl osteoclasts. Thus, independently of a deficiency in V-ATPase, Src, cathepsin-K, and TRAF-6, the gl mutation results in increased number of osteoclasts, characterized by a disrupted cytoskeleton and an underdeveloped ruffled border.

Acid Phosphatase↗
PubMed1999

Frequent loss of heterozygosity at the DNA mismatch-repair loci hMLH1 and hMSH3 in sporadic breast cancer.

To study the involvement of DNA mismatch-repair genes in sporadic breast cancer, matched normal and tumoral DNA samples of 22 patients were analysed for genetic instability and loss of heterozygosity (LOH) with 42 microsatellites at or linked to hMLH1 (3p21), hMSH2 (2p16), hMSH3 (5q11-q13), hMSH6 (2p16), hPMS1 (2q32) and hPMS2 (7p22) loci. Chromosomal regions 3p21 and 5q11-q13 were found hemizygously deleted in 46% and 23% of patients respectively. Half of the patients deleted at hMLH1 were also deleted at hMSH3. The shortest regions of overlapping (SRO) deletions were delimited by markers D3S1298 and D3S1266 at 3p21 and by D5S647 and D5S418 at 5q11-q13. Currently, the genes hMLH1 (3p21) and hMSH3 (5q11-q13) are the only known candidates located within these regions. The consequence of these allelic losses is still unclear because none of the breast cancers examined displayed microsatellite instability, a hallmark of mismatch-repair defect during replication error correction. We suggest that hMLH1 and hMSH3 could be involved in breast tumorigenesis through cellular functions other than replication error correction.

Adaptor Proteins, Signal Transducing↗
PubMed1998

The tRNA(guanine-26,N2-N2) methyltransferase (Trm1) from the hyperthermophilic archaeon Pyrococcus furiosus: cloning, sequencing of the gene and its expression in Escherichia coli.

The structural gene pfTRM1 (GenBank accession no. AF051912), encoding tRNA(guanine-26, N 2- N 2) methyltransferase (EC 2.1.1.32) of the strictly anaerobic hyperthermophilic archaeon Pyrococcus furiosus, has been identified by sequence similarity to the TRM1 gene of Saccharomyces cerevisiae (YDR120c). The pfTRM1 gene in a 3.0 kb restriction DNA fragment of P.furiosus genomic DNA has been cloned by library screening using a PCR probe to the 5'-part of the corresponding ORF. Sequence analysis revealed an entire ORF of 1143 bp encoding a polypeptide of 381 residues (calculated molecular mass 43.3 kDa). The deduced amino acid sequence of this newly identified gene shares significant similarity with the TRM1- like genes of three other archaea (Methanococcus jannaschii, Methanobacterium thermoautotrophicum and Archaeoglobus fulgidus), one eukaryon (Caenorhabditis elegans) and one hyperthermophilic eubacterium (Aquifex aeolicus). Two short consensus motifs for S-adenosyl-l-methionine binding are detected in the sequence of pfTrm1p. Cloning of the P.furiosus TRM1 gene in an Escherichia coli expression vector allowed expression of the recombinant protein (pfTrm1p) with an apparent molecular mass of 42 kDa. A protein extract from the transformed E.coli cells shows enzymatic activity for the quantitative formation of N 2, N 2-dimethylguanosine at position 26 in a transcript of yeast tRNAPhe used as substrate. The recombinant enzyme was also shown to modify bulk E.coli tRNAs in vivo.

Amino Acid Sequence↗
PubMed1998

High resolution deletion mapping reveals frequent allelic losses at the DNA mismatch repair loci hMLH1 and hMSH3 in non-small cell lung cancer.

To study the involvement of DNA mismatch repair genes in non-small cell lung cancer, matched normal and tumoral DNA samples from 31 patients were analyzed for both LOH and microsatellite instability with 34 markers at or linked to hMLH1 (3p21), hMSH2 (2p16), hMSH3 (5q11-q13), hMSH6 (2p16), hPMS1 (2q32), and hPMS2 (7p22) loci. Chromosomal regions 3p21 and 5q11-q13 were found to be hemizygously deleted in 55% and 42% of the patients, respectively. Sixty five percent of the patients deleted at hMLH1 were also deleted at hMSH3. The shortest regions of overlap for 3p21 and 5q11-q13 deletions delimited by D3S1561/D3S1612 and D5S2107/D5S624, respectively, were restricted to genetic distances of only 1 cM. Currently, the hMLH1 (3p21) and hMSH3 (5q11-q13) genes are the only known candidates located within these regions. The mutational analysis of hMLH1 and hMSH3 in hemizygously deleted patients led to the detection of 2 new polymorphisms in hMSH3. The consequence of these allelic losses remains unclear, but the lack of inactivating mutation might explain that replication error, the hallmark of mismatch repair genes inactivation in cancer cells, was quasi-absent in tumors. We suggest that hMLH1 and hMSH3 genes could be involved in lung tumorigenesis through dosage effect in cellular functions other than replication error correction.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Allelic losses and DNA methylation at DNA mismatch repair loci in sporadic colorectal cancer.

Normal and tumor DNA samples of 35 patients with sporadic colorectal carcinoma were analyzed for microsatellite alterations at 12 markers linked to mismatch repair loci: hMLH1, hMSH2, hMSH3, hMSH6, hPMS1 and hPMS2. Remarkably, no correlation was observed between the replication error phenotype (RER+) and allelic losses at these loci. Hemizygous deletions, seen in 6/35 (17%) informative cases at hMLH1, 4/27 (15%) at hMSH2/hMSH6 and 6/34 (18%) at hMSH3, were rarely found in RER+ tumors. Since mismatch repair protein components act in molecular complexes of defined stoichiometry we propose that hemizygous deletion of the corresponding loci may be involved in colorectal tumorigenesis through defects in cellular functions other than replication error correction. The analysis of the methylation status of the promoter region of hMLH1 revealed that methylation might be an important mechanism of this locus inactivation in RER+ sporadic colorectal cancer.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Microsatellite instability in childhood T cell acute lymphoblastic leukemia.

Acute lymphoblastic leukemia (ALL) is the most frequent cancer encountered in children. Little is known about the molecular pathology of childhood T cell ALL. Oncogenesis is a multistep process that involves alterations in proto-oncogenes and tumor suppressor genes. Recently, a mutator phenotype detectable by microsatellite instabilities was shown to be associated with predisposition to cancer. This new mechanism for human carcinogenesis is caused by defects in the DNA replication/repair system. To study the involvement of some of these mutational events in the development of T cell ALL, we have initiated a systematic search for losses of heterozygosity (LOH) and microsatellite instabilities in children affected with this disease. These patients were allelotyped by PCR using 56 microsatellite markers located near known or putative tumor suppressor genes. The microsatellite patterns were altered in more than 80% of the patients. LOH were detected in chromosomes 6p, 12p and 9p. Two third of the patients were deleted for chromosome 9p21, suggesting the involvement of a tumor suppressor gene, probably the p16 gene. The only patient refractory to chemotherapy was shown to be associated with a mutator phenotype. This is the first documented case of a childhood neoplasia associated with genomic instabilities. Our results suggest that defects in DNA replication/repair components are involved in the development of a subset of childhood T cell ALL.

Adolescent↗
PubMed1995

A novel enzymatic pathway leading to 1-methylinosine modification in Haloferax volcanii tRNA.

Transfer RNAs of the extreme halophile Haloferax volcanii contain several modified nucleosides, among them 1-methylpseudouridine (m1 psi), pseudouridine (psi), 2'-0-methylcytosine (Cm) and 1-methylinosine (m1l), present in positions 54, 55, 56 and 57 of the psi-loop, respectively. At the same positions in tRNAs from eubacteria and eukaryotes, ribothymidine (T-54), pseudouridine (psi-55), non-modified cytosine (C-56) and non-modified adenosine or guanosine (A-57 or G-57) are found in the so-called T psi-loop. Using as substrate a T7 transcript of Haloferax volcanii tRNA(Ile) devoid of modified nucleosides, the enzymatic activities of several tRNA modification enzymes, including those for m1 psi-54, psi-55, Cm-56 and m1l-57, were detected in cell extracts of H.volcanii. Here, we demonstrate that modification of A-57 into m1l-57 in H.volcanii tRNA(Ile) occurs via a two-step enzymatic process. The first step corresponds to the formation of m1A-57 catalyzed by a S-adenosylmethionine-dependent tRNA methyltransferase, followed by the deamination of the 6-amino group of the adenine moiety by a 1-methyladenosine-57 deaminase. This enzymatic pathway differs from that leading to the formation of m1l-37 in the anticodon loop of eukaryotic tRNA(Ala). In the latter case, inosine-37 formation preceeds the S-adenosylmethionine-dependent methylation of l-37 into m1l-37. Thus, enzymatic strategies for catalyzing the formation of 1-methylinosine in tRNAs differ in organisms from distinct evolutionary kingdoms.

Adenosine↗
PubMed1991

The gene for a halophilic glutamate dehydrogenase: sequence, transcription analysis and phylogenetic implications.

We have isolated and sequenced the gene for a putative NADP-dependent glutamate dehydrogenase from the extremely halophilic archaebacterium Halobacterium salinarium. This gene is transcribed as a unique RNA molecule of about 1700 nucleotides. The 5' end of the transcript contains characteristic consensus transcription initiation and promoter sequences observed in halophilic archaebacteria. The encoded polypeptide, with a predicted length of 435 amino acids, shows significant overall homology and conservation of functional domains when compared with different eubacterial and eukaryotic glutamate dehydrogenases. Surprisingly, the archaebacterial protein shares a larger number of identical amino acid residues with homologous polypeptides from higher eukaryotes than with those from unicellular eukaryotes and eubacteria.

Amino Acid Sequence↗