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Biomedical subjects

F S Collins

Publications and source records attributed to F S Collins.

At least 217 records · Page 12Linked to original sources
PubMed1992

Aberrant regulation of ras proteins in malignant tumour cells from type 1 neurofibromatosis patients.

Defects in the NF1 gene have been implicated in the inherited disorder neurofibromatosis type 1, which is characterized by several developmental abnormalities including an increased frequency of benign and malignant tumours of neural crest origin (neurofibromas and neurofibrosarcomas respectively). The NF1 gene encodes a ubiquitous protein homologous to p120GAP, the GTPase-activating protein (GAP) for the products of the ras protooncogenes. When expressed in non-mammalian systems, the region of the NF1 gene homologous to p120GAP produces a protein with GAP-like activity. Here we present evidence that the ras proteins in malignant tumour cell lines from patients with type 1 neurofibromatosis are in a constitutively activated state, as judged by the guanine nucleotide bound to them, and are necessary for cellular proliferation. These cells contain p21ras and p120GAP that are both functionally wild type, but barely any functional NF1 protein. Our results show that the NF1 protein is normally essential for correct negative regulation of ras proteins in the cell, even in the presence of normal p120GAP, and they support the hypothesis that NF1 is a tumour-suppressor gene whose product acts upstream of ras.

Antibodies, Monoclonal↗
PubMed1992

Recent progress toward understanding the molecular biology of von Recklinghausen neurofibromatosis.

The gene for von Recklinghausen neurofibromatosis (NF1) was recently identified by positional cloning and found to code for a large, ubiquitously expressed protein. This protein has both structural and functional similarity to a family of proteins with guanosine triphosphatase-activating properties, involved in the regulation of the protooncogene ras. One of the postulated functions of the NF1 gene product may relate to its ability to regulate ras-mediated cell proliferation. Selective pharmacotherapy directed at downregulating ras may be of benefit to patients with NF1.

Forecasting↗
PubMed1992

Characterization of an intron 12 splice donor mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.

Cystic fibrosis, the most common lethal genetic disease in the white population, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Analysis of DNA from a pancreatic insufficient patient by chemical mismatch cleavage and subsequent DNA sequencing led to the identification of a potential splice mutation in the CFTR gene. A transition of the invariant guanosine to adenosine (1898 + 1G > A) was found at the splice donor site of intron 12. To determine the effect of this mutation on the patient's CFTR transcripts, RNA from the nasal epithelium was reverse transcribed and amplified by the polymerase chain reaction (RT-PCR). Direct sequencing of the PCR products revealed that the transcript from the chromosome with the 1898 + 1G > A mutation had skipped exon 12 entirely, resulting in a joining of exons 11 and 13. Deletion of exon 12 results in the removal of a highly conserved region which encodes the Walker B consensus sequence of the first nucleotide-binding fold of CFTR.

Adult↗
PubMed1992

Transfection of wild-type CFTR into cystic fibrosis lymphocytes restores chloride conductance at G1 of the cell cycle.

We complemented the Cl- conductance defect in cystic fibrosis lymphocytes by transfection with wild-type cDNA for the cystic fibrosis transmembrane conductance regulator (CFTR). Stable transfectants were selected and subjected to molecular and functional analyses. We detected expression of endogenous CFTR mRNA in several CF and non-CF lymphoid cell lines by PCR. Expression from cDNA in the transfectants was demonstrated by amplifying vector-specific sequences. Both fluorescence and patch-clamp assays showed that transfectants expressing wild-type CFTR acquired properties previously associated with Cl- conductance (GCl) regulation in non-CF lymphocytes: (i) GCl was elevated in the G1 phase of the cell cycle, (ii) cells fixed at G1 increase GCl in response to increased cellular cAMP or Ca2+, (iii) agonist-induced increases in GCl were lost as the cells progressed to the S phase of the cell cycle. The cell cycle and agonist dependent regulation of GCl was not observed in CF lymphocytes transfected with CFTR cDNA containing stop codons in all reading frames at exon 6. Our findings indicate that lymphocytes express functional CFTR since wild-type CFTR corrects the defects in Cl- conductance regulation found in CF lymphocytes. Evaluation of the mechanism of this novel, CFTR-mediated regulation of GCl during cell cycling should provide further insights into the function of CFTR.

B-Lymphocytes↗
PubMed1992

NF1-related locus on chromosome 15.

A neurofibromatosis type I (NF1)-related locus has been identified on chromosome 15. It contains a partial copy of the NF1 GAP-related domain, which is known to interact with the ras protooncogenes. However, the chromosome 15 sequence contains multiple deletions resulting in frameshift mutations and stop codons in several highly conserved sequence blocks. The locus on chromosome 15 therefore represents an NF1 pseudogene. This nonprocessed NF1 pseudogene may produce additional fragments in Southern blotting, pulsed-field gel, and PCR experiments with some NF1 cDNA probes or oligonucleotides. In addition, certain regions of the NF1 gene also cross-hybridize with a locus on chromosome 14. These loci must be considered in mutation analysis of patients with NF1 since aberrant findings may not always reflect changes in the NF1 gene.

Base Sequence↗
PubMed1992

A yeast artificial chromosome contig encompassing the type 1 neurofibromatosis gene.

The yeast artificial chromosome (YAC) system (Burke et al., 1987, Science 236: 806-812) allows the direct cloning of large regions of the genome. A YAC contig map of approximately 700 kb encompassing the region surrounding the type 1 neurofibromatosis (NF1) locus on 17q11.2 has been constructed. A single YAC containing the entire NF1 locus has been constructed by homologous recombination in yeast. In the process of contig construction a novel method of YAC end rescue has been developed by YAC circularization in yeast and plasmid rescue in bacteria. YACs containing homology to the NF1 region but mapping to another chromosome have also been discovered. Sequences of portions of the homologous locus indicate that this other locus is a nonprocessed pseudogene.

Base Sequence↗
PubMed1992

Sequence-tagged sites (STSs) spanning 4p16.3 and the Huntington disease candidate region.

The generation of sequence-tagged sites (STSs) has been proposed as a unifying approach to correlating the disparate results generated by genetic and various physical techniques being used to map the human genome. We have developed an STS map to complement the existing physical and genetic maps of 4p16.3, the region containing the Huntington disease gene. A total of 18 STSs span over 4 Mb of 4p16.3, with an average spacing of about 250 kb. Eleven of the STSs are located within the primary candidate HD region of 2.5 Mb between D4S126 and D4S168. The availability of STSs makes the corresponding loci accessibility to the general community without the need for distribution of cloned DNA. These STSs should also provide the means to isolate yeast artificial chromosome clones spanning the HD candidate region.

Base Sequence↗
PubMed1992

The gene for a novel epidermal antigen maps near the neurofibromatosis 1 gene.

Recently the M17S1 gene, encoding an epidermal antigen thought to play a role in cell adhesion, was mapped to chromosome bands 17q11-q12, placing it in the vicinity of the gene for the genetic disorder neurofibromatosis 1 (NF1). The pleomorphic cutaneous lesions of NF1 and the precedent for other genes being embedded within the NF1 gene prompted us to investigate whether the M17S1 gene mapped near, or within, the NF1 gene. Genetic linkage analyses revealed that M17S1 was tightly linked to NF1 and mapped within the interval bounded by D17S58 and D17S54. Physical mapping of an M17S1 cDNA on somatic cell hybrids, yeast artificial chromosomes, and an NF1 patient with a deletion involving an entire NF1 allele demonstrated that M17S1 is located at least 180 kb centromeric to the NF1 gene. The distance between the genes suggests that M17S1 is unlikely to contribute to the NF1 phenotype since a gross chromosomal rearrangement would be required to disrupt expression of both genes.

Animals↗
PubMed1992

Phylogenetic footprinting reveals a nuclear protein which binds to silencer sequences in the human gamma and epsilon globin genes.

Tissue- and developmental stage-specific expression of the human beta-like globin genes is regulated by a combination of ubiquitous and erythroid-restricted trans factors that bind to cis elements near each of the five active genes. Additional interactions of these cis and trans factors with sequences located in the far 5' end of the cluster occur by as yet obscure mechanisms. Because of the complexity of this regulatory puzzle, precise identification of the determinants that control hemoglobin switching has proven difficult. Phylogenetic footprinting is an evolutionary approach to this problem which is based on the supposition that the basic mechanisms of switching are conserved throughout mammalian phylogeny. Alignment of the 5' flanking regions of the gamma genes of several species allows the identification of footprints of 100% conserved sequence. We have now tested oligomers spanning 13 such phylogenetic footprints and find that 12 are bound by nuclear proteins. One conserved element located at -1086 from the gamma genes exhibits repressor activity in transient transfection studies. The protein that binds this element, CSBP-1 (conserved sequence-binding protein 1), also binds at three sites within a silencer element upstream from the epsilon globin gene. Further analysis reveals that the CSBP-1 binding activity is identical to that of a recently cloned zinc finger protein that has been shown to act as a repressor in other systems. The binding of CSPB-1 to silencer sequences in the epsilon and gamma globin genes may be important in the stage-specific silencing of these genes.

Animals↗
PubMed1992

Sequencing and analysis of genomic fragments from the NF1 locus.

The sequence of five non-contiguous genomic fragments encompassing 14.4 kilobases from the NF1 locus have been determined by fluorescence-based automated DNA sequence analysis. These fragments included one kilobase of the NF1 coding region, which resulted in the identification of the intron/exon boundaries of five exons. Based on these sequences, five new NF1 exon-PCR assays have been developed, that could be useful for detecting new NF1 mutations. The genomic sequences were analyzed for the presence of Alu repetitive elements and their classification is described. This analysis may provide some insight into the characterization of genetic rearrangements resulting in disruption of the NF1 gene.

Base Sequence↗
PubMed1992

A recombination event that redefines the Huntington disease region.

We report both a recombination event that places the Huntington disease gene proximal to the marker D4S98 and an extended linkage-disequilibrium study that uses this marker and confirms the existence of disequilibrium between it and the HD locus. We also report the cloning of other sequences in the region around D4S98, including a new polymorphic marker R10 and conserved sequences that identify a gene in the region of interest.

Chromosomes, Human, Pair 4↗
PubMed1991

Chloride conductance expressed by delta F508 and other mutant CFTRs in Xenopus oocytes.

The cystic fibrosis transmembrane conductance regulator (CFTR) is associated with expression of a chloride conductance that is defective in cystic fibrosis (CF). Xenopus oocytes injected with RNA coding for CFTR that contained mutations in the first nucleotide binding fold (NBF1) expressed chloride currents in response to raising adenosine 3',5'-monophosphate (cAMP) with forskolin and 3-isobutyl-1-methylxanthine (IBMX). The mutant CFTRs were less sensitive than wild-type CFTR to this activating stimulus, and the reduction in sensitivity correlated with the severity of cystic fibrosis in patients carrying the corresponding mutations. This demonstration provides the basis for detailed analyses of NBF1 function and suggests potential pharmacologic treatments for cystic fibrosis.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Identification of the neurofibromatosis type 1 gene product.

The gene for neurofibromatosis type 1 (NF1) was recently identified by positional cloning. The complete cDNA encodes a polypeptide of 2818 amino acids. To study the NF1 gene product, antibodies were raised against both fusion proteins and synthetic peptides. Initial characterization of two anti-peptide antibodies and one fusion-protein antibody demonstrated a specific protein of approximately 250 kDa by both immunoprecipitation and immunoblotting. This protein was found in all tissues and cell lines examined and is detected in human, rat, and mouse tissues. To demonstrate that these antibodies specifically recognize the NF1 protein, additional fusion proteins containing the sequence specific to the synthetic peptide were generated. Both peptide antisera recognize the proper specific fusion proteins so generated. Immunoprecipitates using the peptide antisera were shown to recognize the same protein detected by immunoblotting with either the other peptide antiserum or the fusion-protein antiserum. Immunoblotting using antiserum specific to spatially distinct epitopes conducted on tissue homogenates demonstrated the NF1 protein in all adult tissues. Based on the homology between the NF1 gene product and members of the GTPase-activating protein (GAP) superfamily, the name NF1-GAP-related protein (NF1GRP) is suggested.

Amino Acid Sequence↗
PubMed1991

A de novo Alu insertion results in neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder with a high mutation rate and variable expression, characterized by neurofibromas, café-au-lait spots, Lisch nodules of the iris, and less frequent features including bone deformities and learning disabilities. The recently cloned NF1 gene encodes a transcript of 13 kilobases from a ubiquitously expressed locus on chromosome 17. Most NF1 patients are expected to have unique mutations, but only a few have so far been characterized, restricting genetic and functional information and the design of DNA diagnostics. We report an unusual NF1 mutation, that of a de novo Alu repetitive element insertion into an intron, which results in deletion of the downstream exon during splicing and consequently shifts the reading frame. This previously undescribed mechanism of mutation indicates that Alu retrotransposition is an ongoing process in the human germ line.

Adult↗