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Biomedical subjects

R A Wells

Publications and source records attributed to R A Wells.

At least 19 recordsLinked to original sources
PubMed1992

FRA2B is distinct from inverted telomere repeat arrays at 2q13.

Human chromosome 2 was formed by a telomere-to-telomere fusion of two ancestral ape chromosomes. The fusion point is localized in chromosomal band 2q13, which also contains the rare, folate-sensitive fragile site FRA2B. It has been hypothesized that this fragile site may be related to the presence of interstitial telomeric and subtelomeric sequences, which have come to lie in an inverted repeat arrangement as a result of the fusion event. Fluorescence in situ hybridization of a genomic cosmid c8.1, which spans the fusion point, was carried out on metaphase spreads of an individual who expressed the fragile site at 2q13. We show that the fusion point maps distal to this fragile site. Therefore, we conclude that the inverted arrays of telomeric and subtelomeric sequences found at this fusion point are unlikely to correspond to the rare fragile site at 2q13.

Base Sequence↗
PubMed1992

Multiple variants in subtelomeric regions of normal karyotypes.

We describe a human genomic cosmid clone, 56.1.1, that contains subtelomeric sequences present on multiple human chromosomes. In particular, using fluorescence in situ hybridization, we have identified 16 sites of hybridization on 12 chromosomes. In a sample of 8 unrelated individuals, 10 of these sites showed interindividual variation. Co-hybridization with other polymorphic probes allowed us to demonstrate cytologically heterozygosity at three sites in six individuals. The chromosomal distribution of hybridization sites in a family strongly suggests that these variants are inherited in a Mendelian fashion. These data show that subtelomeric repeats are a rich source of genetic variability. Possible mechanisms of generation of such variants are discussed.

Chromosomes, Human↗
PubMed1991

Origin of human chromosome 2: an ancestral telomere-telomere fusion.

We have identified two allelic genomic cosmids from human chromosome 2, c8.1 and c29B, each containing two inverted arrays of the vertebrate telomeric repeat in a head-to-head arrangement, 5'(TTAGGG)n-(CCCTAA)m3'. Sequences flanking this telomeric repeat are characteristic of present-day human pretelomeres. BAL-31 nuclease experiments with yeast artificial chromosome clones of human telomeres and fluorescence in situ hybridization reveal that sequences flanking these inverted repeats hybridize both to band 2q13 and to different, but overlapping, subsets of human chromosome ends. We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2.

Base Sequence↗
PubMed1990

Genetic alteration of normal aging processes is responsible for extended longevity in Drosophila.

The first step in a genetic analysis of aging is to identify and characterize the genetic mutants and their controls that will be used. Such mutants or strains are initially identified by their effect on the life span. Yet many genetic interventions are known to have some effect on the life span without necessarily affecting the aging process. It is therefore necessary to prove that one is actually dealing with an aging mutant before one draws strong inferences from the data. Casarett's rules provide an operational test for doing so, relying as they do on the comparison of aging bio-markers in the experimental and reference strains. We show that our previously described genetically based long-lived NDC-L strain and its normal-lived NDC-R control strain differ only in the chronological age of expression of two behavioral and three physiological functional age biomarkers. They do not differ in the sequence or the physiological age of expression of these biomarkers. These two strains comply with the Casarett rules and thereby comprise a valid tool with which to conduct a comparative genetic analysis of aging. The implications of the available data are discussed, including the possibility that aging in these strains of Drosophila melanogaster may be the result of a multiphasic developmental process.

Aging↗
PubMed1990

Telomere-related sequences at interstitial sites in the human genome.

The ends (telomeres) of eukaryotic chromosomes are protected from degradation and from loss during DNA replication by buffers of simple tandem repetitive sequence. The nucleotide sequence of these telomeric arrays is fundamental to telomere function as a site for protein and ribonucleoprotein binding and varies only slightly in a wide range of organisms. We present evidence that arrays of this human telomeric sequence, TTAGGG, are present not only at the ends of human chromosomes but also at numerous interstitial sites. These interstitial loci share nucleotide sequence similarity outside the repetitive array, suggesting that they are related functionally or have evolved from a common progenitor locus.

Base Sequence↗
PubMed1989

Hypervariable minisatellites: recombinators or innocent bystanders?

It has become apparent in recent years that unexpectedly large numbers of minisatellites exist within the eukaryotic genome. Their use in genetics is well known, but as with any new class of sequence, there is also much speculation about their involvement in a range of biological processes. How much is known of their biology?

Base Sequence↗
PubMed1989

Simultaneous genetic mapping of multiple human minisatellite sequences using DNA fingerprinting.

We have used several DNA probes which simultaneously recognize multiple loci to follow the segregation of a large number of minisatellite loci through two large reference pedigrees. The segregation data were analyzed for linkage to previously characterized marker loci using RFLP mapping data for these pedigrees from a previous study and from the Centre d'Etude du Polymorphisme Humain data bank. In this way we have mapped 31 separate minisatellite alleles of a total of 146 studied. The results of these analyses suggest that the distribution of minisatellites in the human genome is skewed toward telomeres and is highly clustered in character. A group of at least five separate minisatellites was found at 7 qter, and smaller clusters are present in several other regions. We detected a smaller than expected number of linkages, perhaps because of the clustering of minisatellite loci. The 7qter minisatellite cluster is in a region of excess male meiotic recombination, and in this respect is similar to minisatellite clusters at 16pter and in the X-Y pseudoautosomal region.

Alleles↗
PubMed1988

Metabolic rates in genetically based long lived strains of Drosophila.

The goal of these experiments was to determine if the increased longevity characteristics of our genetically selected long lived line of Drosophila could be attributed to metabolic differences. The data shows an inverse relationship between life span and temperature for both the long lived (L) and normal (R) strains; however, the higher longevity of the L strain relative to the R strain is not affected by these treatments. Therefore, the genetic factors unique to the L strain do not affect the same processes affected by the temperature treatments. A second set of experiments detected a linear relationship between the MDMR (mean daily metabolic rate) and the ambient adult temperature. However, at each temperature, the MDMR of either strain was statistically equivalent; a finding which demonstrates that an increased life span depends on something other than conservation of calories. A third set of experiments looked at the metabolic efficiency of the two strains and were not able to detect any statistically significant differences. The two strains appear to expend approximately equivalent numbers of calories per day in an approximately equivalent manner. These data are interpreted in the context both of a previously postulated genetic switch mechanism believed responsible for initiating the onset of senescence, and of contemporary reinterpretations of the "rate of living" theory which implicates the essential role of various anti-oxidant defense systems.

Aging↗
PubMed1988

Prediction of consanguinity using human DNA fingerprints.

DNA fingerprinting was performed to verify the pedigree structure of a family under investigation for an unusual case of beta thalassaemia. A higher than expected proportion of hypervariable bands was shared by the proband and his mother, leading to suspicion that the child had been the product of a consanguineous mating. Further analysis of the mother's brother showed that he was almost certainly the proband's father.

Child, Preschool↗
PubMed1988

Assessment of clonality in gastrointestinal cancer by DNA fingerprinting.

DNA fingerprinting with three different probes (33.15, 33.6, and alpha-globin 3'HVR) was investigated as a method for the determination of clonality in gastrointestinal tumors. In 29/44 carcinomas the tumor DNA showed clonal somatic mutations that were not seen in the corresponding peripheral blood and normal mucosa samples. The changes consisted of either novel fingerprint bands, losses of bands, or both. The probe 33.15 yielded the highest rate of abnormal DNA fingerprints (21/44 carcinomas). Sequential use of the probes increased the number of cases where clonal fingerprint markers could be detected. One out of five colorectal adenomas also showed a clonal loss of a fingerprint band. In two cases of gastric cancer, DNA from the metastatic tumor had a different DNA fingerprint from that found in the primary carcinoma. DNA fingerprinting offers a novel approach to determining clonality in tumors and may prove useful for the study of tumor progression.

Cloning, Molecular↗
PubMed1979

Loss of circulating T lymphocytes with normal levels of B and 'null' lymphocytes in Thai adults with malaria.

Peripheral blood mononuclear cells from forty-nine Thai adults infected with either Plasmodium falciparum or Plasmodium vivax were examined in order to determine the percentage of T, B, and Fc-receptor-bearing cells present. In comparison to healthy controls, both the percentage and concentration of peripheral T cells were decreased in the malaria-infected individuals as assessed by formation of rosettes with sheep red blood cells. The percentage of peripheral B cells was increased but their concentration was unchanged, as assessed by two techniques: the presence of surface immunoglobulin and the presence of a complement receptor. Both the percentage and concentration of lymphocytes bearing Fc receptors were unchanged in infected individuals. Finally, calculation of the changes in 'null' cells (defined either as non-T, non-B lymphocytes or as non-T, non-B, non Fc-receptor-bearing lymphocytes) revealed an increase in the 'null' cell percentage but a decrease in the absolute number of 'null' cells. These data indicate that in adult Thai patients naturally infected with malaria, there is a real loss of circulating T lymphocytes with no real change in B, Fc-receptor-bearing, or 'null' lymphocytes.

Adolescent↗
PubMed1978

The results of family therapy revisited: the nonbehavioral methods.

Studies from 1971 to 1976 reporting on the outcome of the nonbehavioral family therapies are analyzed and critically reviewed. Such research has increased in both quality and quantity since 1970 and, broadly speaking, has legitimized the status of family therapy as a viable mode of helping. Particularly potent effects were noted for family therapy as an alternative to psychiatric hospitalization, with psychosomatic problems in children and adolescents, and in certain applications with parent-child and parent-adolescent relationships. However, a number of studies comparing family therapy with no formal treatment or an alternative treatment found little difference in outcome. Problems in family therapy outcome research are discussed and some future directions suggested.

Adolescent↗
PubMed1978

Ideologies, idols (and graven images?): rejoinder to Gurman and Kniskern.

Three major issues raised in Gurman and Kniskern's commentary are discussed. These are (a) the suitability of established research design criteria for studying the outcome of family therapy; (b) the impact of therapist relationship factors on therapy outcome; and (c) the place of concrete or objective change measures in psychotherapy outcome research. Areas of agreement and disagreement with Gurman and Kniskern's observations are identified.

Attitude of Health Personnel↗
PubMed1977

Cyclophosphamide-induced specific suppression of the protective immune response to rodent malaria.

Nonspecific and specific chemosuppression of the immune response to Plasmodium berghei protective antigens were investigated. Specific immunosuppression was defined operationally as the selective suppression of the protective response to the parasite in mice injected with a combination of gamma-irradiated infected mouse erythrocytes (gammaPb) and cyclophosphamide (CY) with continued responsiveness to sheep erythrocytes (SRBC). After initial treatment (gammaPb + CY), mice were injected with gammaPb in potentially immunogenic doses. These and appropriate control animals were later challenged with nonirradiated infected mouse erythrocytes. The influence of the initial treatment regimens on the protective response was evaluated by parasitemia, and mortality was observed after challenge. Specificity of suppression was measured by evaluating the ability of mice to produce antibody to SRBC. Both specific and nonspecific suppression of the protective response to malaria were noted. Initial treatment with drug alone resulted in increased parasitemia and mortality and suppression of the SRBC antibody synthesis in drug-pretreated immunized mice as compared with immunized mice not pretreated with the drug. On the other hand, suppression of the response to the parasite, but not to SRBC, in animals pretreated with gammaPb + CY was clearly greater than that induced by drug alone. Thus, animals treated with malarial antigen and cyclophosphamide develop a measurable specific immunosuppression. These studies indicate that immunity to malaria is influenced by both cyclophosphamide alone (general immunosuppression) and cyclophosphamide in combination with antigen (specific immunosuppression) in a manner analogous to other immune responses.

Animals↗