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J M Coffin

Publications and source records attributed to J M Coffin.

At least 19 recordsLinked to original sources
PubMed1992

Mls-1 is encoded by the long terminal repeat open reading frame of the mouse mammary tumor provirus Mtv-7.

The murine Mls-1 antigen is the prototype of endogenous superantigens, molecules whose activities lead to deletion of T cells expressing certain T-cell receptor V beta genes from the mature repertoire. However, Mls-1 also stimulates T cells expressing these particular V beta genes (V beta 6, V beta 7, V beta 8.1, and V beta 9) in vitro, making it one of the strongest known T-cell activators. We have recently reported that the Mls-1 gene is closely linked to the endogenous mammary tumor virus Mtv-7. We now demonstrate that Mls-1 is encoded by the open reading frame in the U3 region of the long terminal repeat of Mtv-7. However, control of expression of this molecule seems complex, depending on the promoter used for the transfection experiments. The sequence of the Mtv-7 open reading frame differs from all other known mammary tumor virus open reading frame sequences in the 3' end, suggesting that the T-cell receptor V beta specificity is conferred by the C terminus of the molecule. The predicted structure of the protein encoded by the open reading frame is consistent with a type II transmembrane molecule where the C terminus is extracellular.

Amino Acid Sequence↗
PubMed1992

Nonrandom integration of retroviral DNA in vitro: effect of CpG methylation.

We have developed a PCR-based system that allows us to assess the relative frequency of use of specific bases as targets for the avian leukosis virus in vitro integration system. Using this system, we tested the effect of 5-methylation of cytosine in runs of CpG on the distribution of integration target sites. We found that the distribution of preferred integration sites was not uniform along the target DNA; rather, there was a distinct and reproducible pattern of frequently used sites. This pattern was independent of orientation of the integrated DNA, and of overall structure and sequence of the target and fragment amplified. Methylation did not inhibit integration into CpG dinucleotides; on the contrary, this modification created highly preferred targets within runs of alternating CpG. Finally, similar but not identical specificity was observed by using preintegration complexes in infected extracts or purified integrase and DNA as enzyme and substrate. Thus, most of the specificity observed is conferred by interaction of integrase and targets, although it may be modified by other viral and/or cellular components.

Animals↗
PubMed1992

Mechanism of transduction by retroviruses.

Retroviruses can capture cellular sequences and express them as oncogenes. Capture has been proposed to be a consequence of the inefficiency of polyadenylation of the viral genome that allows the packaging of cellular sequences flanking the integrated provirus in virions; after transfer into virions, these sequences could be incorporated into the viral genome by illegitimate recombination during reverse transcription. As a test for this hypothesis, a tissue culture system was developed that mimics the transduction process and allows the analysis and quantitation of capture events in a single step. In this model, transduction of sequences adjacent to a provirus depends on the formation of readthrough transcripts and their transmission in virions and leads to various recombinant structures whose formation is independent of sequence similarity at the crossover site. Thus, all events in the transduction process can be attributed to the action of reverse transcriptase on readthrough transcripts without involving deletions of cellular DNA.

Base Sequence↗
PubMed1992

Characterization of the endogenous nonecotropic murine leukemia viruses of NZB/B1NJ and SM/J inbred strains.

We characterized 84 endogenous nonecotropic proviruses of NZB/B1NJ and SM/J inbred strains by examining proviral junction fragment segregation in recombinant inbred (RI) and backcross mice. Forty-five proviruses were shared with other laboratory strains, but 28 were unique to NZB/B1NJ or SM/J. Proviral loci were located on 17 of the 19 mouse autosomes and on both sex chromosomes. These markers will facilitate gene mapping in the NXSM RI set and contribute to the pursuit of a more complete map of the mouse genome.

Animals↗
PubMed1992

Mapping of the motor neuron degeneration (Mnd) gene, a mouse model of amyotrophic lateral sclerosis (ALS).

The motor neuron degeneration mutation (Mnd) causes a late-onset, progressive degeneration of upper and lower motor neurons in mice. After establishing genetic and environmental conditions that distinguish the phenotypes of Mnd/Mnd from +/Mnd mice, Mnd was mapped to proximal Chr 8, using endogenous retroviruses as markers. The map location was confirmed with additional linked polymorphic markers. The outcross/intercross matings to the strain AKR/J, which were used to follow the segregation of the retroviral markers with respect to Mnd, also revealed the existence of a timing effect. Approximately one-fourth of the affected Mnd/Mnd F2 progeny showed accelerated disease. The Mnd mouse model should allow study of mechanisms affecting onset and progression of specific neuronal degeneration in both animal and human neurological disease.

Age Factors↗
PubMed1992

Retroviral DNA integration.

This overview summarizes the properties and mechanism of retroviral DNA integration and the consequences of the integration process to the infected cell and host. Integration of viral into cellular DNA is a regular and irreversible event, essential for virus replication, whose mechanism is becoming well understood. Many pathogenic consequences of retrovirus infection are due to side-effects of the integration process, including gene disruption, activation of proto-oncogenes, acquisition of oncogenes, and inappropriate expression of viral gene products. The properties and risks associated with these events are reviewed along with overall conclusions as to the importance of these to possible retroviral contaminants of biologicals.

Animals↗
PubMed1991

Genes for epilepsy mapped in the mouse.

The neurological mutant mouse strain E1 is a model for complex partial seizures in humans. The inheritance of epileptic seizures with seven conventional chromosomal markers and over 60 endogenous proviral markers was studied by means of back-crosses of E1 with two seizure-resistant strains, DBA/2J and ABP/LeJ. The major gene responsible for this epileptic phenotype (El-1) was localized to a region distal with respect to the centromere on chromosome 9. At least one other gene, El-2, linked to proviral markers on chromosome 2, also influences the seizure phenotype. In addition, a potential modifier of seizures was detected in the DBA/2J background. The location of El-1 on distal chromosome 9 may allow identification of an epilepsy candidate gene in humans on the basis of conserved synteny with human chromosome 3.

Animals↗
PubMed1991

Linkage of Mls genes to endogenous mammary tumour viruses of inbred mice.

T cells that recognize self antigen are clonally deleted in the thymus--a maturation process that occurs in the context of histocompatibility molecules and the T-cell receptor. The minor lymphocyte stimulation antigens (Mls) effect these deletions through interactions with the V beta portion of the T-cell receptor, thus mimicking bacterial 'superantigens'. Intrigued by the fact that each known Mls gene maps to the same chromosomal region as an endogenous mouse mammary tumour virus (Mtv), we reevaluated the linkage relationships between the two gene families. Here we report perfect concordance in inbred and recombinant inbred mice between the presence of four Mtv proviruses with the expression of Mls gene products. These data suggest a general model in which mammary tumour virus gene products themselves are the ligands that shape a considerable portion of the immunological repertoire of common laboratory mice.

Animals↗
PubMed1991

Effect of BMY 21502 on classical conditioning of the eyeblink response in young and older rabbits.

BMY 21502, a substituted pyrrolidionone, has been found to enhance a simple form of learning in older rabbits. In humans, this simple type of learning, classical conditioning of the eyeblink response, declines in normal aging and is seriously impaired in Alzheimer's disease (AD). We have demonstrated that eyeblink classical conditioning reliably discriminates patients diagnosed with probable AD from non-demented, age-matched elderly subjects. Older organisms can be classically conditioned, but they condition at a much slower rate than younger organisms. Our preliminary analyses indicate age differences in distribution of protein kinase C in the hippocampus. Here we also report that older rabbits that are administered two different doses of BMY 21502 classically condition at a rate approximating that of young rabbits.

Aging↗
PubMed1991

Virological events leading to spontaneous AKR thymomas.

The spontaneous leukemias of AKR mice are caused by mink cell focus-forming (MCF) viruses. These viruses are generated by recombination between several endogenous murine retroviruses. The virological events leading to the generation of the leukemogenic agent were investigated by using an oligonucleotide specific for the U3 region of the leukemogenic virus and env-reactive oligonucleotide probes specific for the different classes of endogenous murine leukemia virus. It was shown that (i) the leukemogenic MCF virus is formed by recombination between at least three different endogenous sequences; (ii) the U3 donor for the leukemogenic virus is the inducible xenotropic virus Bxv-1; (iii) all spontaneous tumors contain viruses with duplicated enhancer regions in their long terminal repeats; (iv) enhancer duplication is a somatic event, since Bxv-1 contains only one copy; (v) the first recombinant virus detectable in mass populations of thymocytes by Southern hybridization analysis contains all structural features of the ultimate leukemogenic virus; and (vi) the multiple novel viruses in a given tumor represent progeny of the same unique recombination events. On the basis of these results, an analysis of the virological events leading to AKR thymomas is presented.

Animals↗
PubMed1991

Characterization of endogenous and recombinant proviral elements of a highly tumorigenic AKR cell line.

As an approach to evaluating the contribution of classes of endogenous viral sequences to leukemogenesis, a genomic library was prepared from the highly tumorigenic AKR SL12.3 cell line and screened for env-containing proviruses. An extensive battery of virus-derived probes and specific oligonucleotide probes were used to segregate 83 positive clones into related groups. The nonecotropic endogenous retroviruses were identified as members of the polytropic, modified polytropic, or xenotropic groups. At least three unique xenotropic proviruses were detected that differed from the published xenotropic sequence within a variable region of the 5' portion of env. Changes among the xenotropic proviruses included relative insertions and/or deletions that maintain an open reading frame and hence the potential to encode viable envelope gene products. Several recombinant viruses were also detected. Recombination was not random and primarily involved the formation of mink cell focus-inducing class I retroviruses via recombination between polytropic elements and ecotropic virus. One other recombinant was detected which contained ecotropic virus sequences in the 5' region encoding p15 of an otherwise xenotropic provirus. An interesting observation was the finding that certain clones contained more than one provirus within the average 20-kb cloned insert. This would not be expected if integration were totally random. The de novo recombinant proviruses identified here provide a series of potential candidates to be evaluated for their contribution to the tumorigencity of the SL12.3 cell line.

Base Sequence↗
PubMed1991

Relationship of avian retrovirus DNA synthesis to integration in vitro.

An in vitro integration system derived from avian leukosis virus-infected cells supports both intra- and intermolecular integration of the viral DNA. In the absence of polyethylene glycol, intramolecular integration of viral DNA molecules into themselves (autointegration) was preferred. In the presence of polyethylene glycol, integration into an exogenously supplied DNA target was greatly promoted. Analysis of integration intermediates revealed that the strand transfer mechanisms of both reactions were identical to those of retroviruses and some transposons: each 3' end of the donor molecule is joined to a 5' end of the cleaved target DNA. The immediate integration precursor appears to be linear viral DNA with the 3' ends shortened by 2 nucleotides. Finally, in the avian system, most cytoplasmic viral DNA appears to be incomplete and further DNA synthesis is required for integration in vitro.

Avian Leukosis Virus↗
PubMed1990

Isotype switching of an immunoglobulin heavy chain transgene occurs by DNA recombination between different chromosomes.

Transgenic mice carrying an immunoglobulin mu heavy chain transgene exhibit isotype switching of the transgene. We have now characterized the mechanism of transgene switching in these mice. The site of mu transgene insertion in one transgenic line has been localized to chromosome 5 using a series of polymorphic endogenous retroviruses as genetic markers in backcross mice. The endogenous immunoglobulin heavy chain locus resides on mouse chromosome 12, which shows that transgene isotype switching can occur between two different chromosomes even though normal antibody gene switching has generally been thought to occur within one chromosome. We find that transgene isotype switching involves interchromosomal DNA recombination, and our data suggest that the same enzymatic mechanisms mediate both normal isotype switch recombination and interchromosomal transgene switching. Our findings also support the notion that the isotype switching mechanism can induce chromosomal translocations such as observed for the c-myc gene in some B cell tumors.

Animals↗
PubMed1990

Molecular mechanisms of nucleic acid integration.

There are three known mechanisms by which foreign DNA can be made a permanent part of the genome of an animal cell, and their properties are summarized in this report. Naked DNA introduced into cells is usually rapidly lost, but a small fraction can be integrated by illegitimate recombination, usually accompanied by major and unpredictable rearrangements in both inserted DNA and target. This mechanism, although inefficient and disruptive, accounts for virtually all integrated DNA seen in virus infections, and is often used for making cell lines carrying specific genes as well as transgenic mice. Homologous recombination between inserted and resident DNA is much rarer but can be detected and put to use. The best understood mechanism is that employed by retroviruses and related elements. In contrast to the other mechanisms, retroviral integration results in a predictable, stable association between virus and cell DNA with only minor sequence changes. However, it occurs only when the DNA is derived by reverse transcription of the RNA in an incoming viral particle and contains the correct sequences at its ends. Thus, from a standpoint of vaccine safety, only the first of the three mechanisms is at all relevant. Based on some prior experimentation in animals, the risk of introduction of activated oncogenes or other dangerous sequences by this means is extremely small.

Animals↗