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Biomedical subjects

T Bryan

Publications and source records attributed to T Bryan.

At least 19 recordsLinked to original sources
PubMed1997

Telomeres in the haemopoietic system.

The limited life span of most blood cells requires the continuous production of cells, which in adults exceeds 10(12) cells/day. This impressive production of cells (approximately 4 x 10(16) cells over a lifetime) is achieved by the proliferation and differentiation of committed progenitor cells, which themselves are derived from a population of pluripotent stem cells with self-renewal potential. Paradoxically, the large majority of stem cells in adult bone marrow are quiescent cells. One possibility is that stem cells, like other somatic cells, have only a limited replicative potential (< 100 divisions). This hypothesis is supported by two key observations and the consideration that, in theory, 55 divisions can yield 4 x 10(16) cells. First, it was shown that 'candidate' stem cells purified from fetal and adult tissue showed dramatic functional differences in turn-over time and the ability to produce cells with stem cell properties, Second, these functional differences were found to correlate with a measurable loss of telomere repeats despite the presence of low but readily detectable levels of telomerase in all purified cell fractions. In order to address questions about the role of telomeres in normal and malignant haemopoiesis, we developed a quantitative fluorescence in situ hybridization technique. Here we review the characteristics of this novel tool to assess the number of telomere repeats at the end of individual chromosomes and provide an overview of recent observations.

B-Lymphocytes↗
PubMed1996

Analysis of live, oral poliovirus vaccine monopools for human immunodeficiency virus type 1 and simian immunodeficiency virus.

Although there is no evidence for transmission of mammalian retroviruses to humans via vaccine immunization, the allegations of contamination of oral poliovirus vaccines with human immunodeficiency virus (HIV) type 1 or a hypothetical progenitor virus from monkeys has created controversy and dispute regarding the origin of AIDS in humans. Twelve monovalent lots of live, attenuated oral poliovirus vaccine types 1, 2, and 3, which were released for use by a North American manufacturer between 1976-1989, were tested for the presence of HIV-1 and simian immunodeficiency virus (SIV). HIV/SIV were not detected in these monovalent poliovirus vaccine lots with the reverse transcriptase assay, a general detection assay, and highly sensitive and specific polymerase chain reaction assays.

Animals↗
PubMed1995

Teachers' ratings of the social competence and school adjustment of students with LD in elementary and junior high school.

The purpose of this study was to examine whether teachers' judgments of students' social competence and school adjustment differentiated students with learning disabilities (LD) (n = 30; boys = 19, girls = 11) from low-achieving (LA) students (n = 29; boys = 17, girls = 12) and average-achieving (AA) students (n = 33; boys = 18, girls = 15) at two grade levels: third/fourth (mean age = 9.97, SD = 1.09) and seventh/eighth (mean age = 13.63, SD = .65). Teachers completed the Walker-McConnell Scale of Social Competence and School Adjustment for each student. They rated younger students with LD and LA students as having significantly lower social competence and school adjustment than their AA peers. In addition, the results supported the use of teacher ratings for initial screening and identification of elementary students at high risk for social-behavioral problems. However, teachers' ratings did not discriminate LD, LA, and AA students at the older grade levels. The discussion focuses on the utility of teachers' identification of social problems at different grade levels.

Adolescent↗
PubMed1994

Getting caught in misconduct: conceptions of adolescents with and without learning disabilities.

This study examined adolescents' conceptions about how to respond after being caught in misconduct, in order to determine whether students with learning disabilities differ from nondisabled students in their beliefs regarding apprehension. A total of 88 students with learning disabilities (62 male, 26 female) and 84 nondisabled students (45 male, 39 female) were interviewed about 10 scenarios in which a teenager was caught by authorities after participating in misconduct, either alone or with a peer. The mean age of the students was 16 years (SD = 1.4). The results indicated that the students with learning disabilities were significantly more likely than other students to suggest escaping and less likely to suggest accepting the consequences, although the differences were not great. The implications of these findings are discussed.

Adolescent↗
PubMed1994

Doing homework: perspectives of elementary and junior high school students.

A survey of homework experiences was administered to 1,527 elementary and junior high students in regular (n = 1,242), resource (n = 234), and self-contained special education (n = 51) classrooms. The results found significant main effects for Group, Grade, and Group by Grade interactions for items related to amount of, type of, and time spent doing homework; opportunity to do homework at school; parents' assistance; students' beliefs about homework assignments and grading; and students' feelings about homework and school. The higher incidence of negative feelings and opinions from students in resource room programs suggests that students' understanding of assignments, the nature of the assignments, and the feedback given to students are important issues requiring closer evaluation. The results also suggest that changes in homework assignments and grading may make the transition from elementary to junior high school particularly difficult for students with special needs.

Adolescent↗
PubMed1992

Students' expectations about peer pressure to engage in misconduct.

Previous research suggests that students with learning disabilities may differ from other students in their expectations of how peers are likely to propose engaging in misconduct. This study followed up on these findings using a methodology that did not require the participants to produce their responses verbally. Participants were 74 students with learning disabilities (53 male, 21 female) and 85 students without disabilities (40 male, 45 female) from high schools in three types of communities (urban, primarily black; urban, primarily Hispanic; suburban, primarily white). The students were presented with a series of pairs of statements that might be made by a teenager trying to entice a peer into misconduct and were asked to indicate which statement in each pair was the more persuasive. The results partially replicated the earlier research. The methodological and social implications of these results are discussed.

Adolescent↗
PubMed1991

Biochemical and biological comparison of HIV-1 NEF and ras gene products.

Human immunodeficiency virus type 1 (HIV-1) NEF protein has been reported to share certain biochemical and structural properties with known oncoproteins like src or rats. To determine whether this is a general property of NEF from various HIV isolates, three different NEF proteins were expressed in Escherichia coli using a thermoinducible expression system previously exploited to overproduce functionally active p21 ras proteins. ras and NEF proteins expressed in this manner were evaluated in parallel to compare their biochemical and biological properties. In contrast to ras, our NEF protein preparations had no detectable GTP binding but showed autophosphorylation activity when incubated in the presence of either GTP or ATP. This putative autokinase activity was higher in NEF proteins containing threonine at position 15 than in those carrying alanine at that position. Two different NEF genes also failed to induce oncogenic transformation of permanently transfected NIH 3T3 cells under conditions that led to oncogenic transformation using activated ras genes. Also, unlike ras, the NEF gene products failed to induce meiotic maturation when injected into fully grown Xenopus oocytes.

Adenosine Triphosphate↗
PubMed1991

Positive mood and math performance.

Two studies are reported that assessed the impact of positive moods on students' feelings of self-efficacy and math performance. In the first study, 32 black and Hispanic girls and boys in the third to fifth grades, who had been identified by teachers as at risk for school failure, and a control sample of normally achieving classmates served as subjects. In the second study, 15 males and 3 females in junior high and high school attending a private school for students with learning disabilities served as subjects. In both studies, students were randomly assigned to a positive-mood induction condition or a no-treatment control condition. Following this, they completed a measure of self-efficacy for math and were then given 5 minutes to do 50 math problems. In both studies, analyses of covariance using standardized math scores as the adjustor variable found that children in the positive-mood condition completed significantly more problems accurately than children in the no-treatment control condition. In addition, in the junior high and high school sample, students in the positive-mood induction condition expressed greater self-efficacy for math than students in the control condition. The results of these two studies raise many questions about the role of affect, positive and negative, in the learning and performance of students with learning disabilities that researchers and teachers might explore.

Adolescent↗
PubMed1991

Popliteal arterial injuries associated with fractures or dislocations about the knee as a result of blunt trauma.

A total of 73 patients with popliteal arterial injuries due to blunt trauma were treated at the Los Angeles County/University of Southern California Medical Center between January 1975 and January 1986. The injuries resulted from high-energy trauma (70% were motor-vehicle-related), and were associated with a variety of fractures and dislocations about the knee. Forty-eight of the patients (66%) had open injuries, 27% of which became infected; the infection rate for all injuries was 22%. The average time from injury to anastomosis was 14.6 hours. The overall amputation rate in the series was 15%. Ten of the 11 amputations were associated with open, type III fractures. The amputation rate did not correlate with type of fracture, delay in diagnosis, or delay in surgery of up to 24 hours, but was directly related to the degree of soft-tissue trauma.

Academic Medical Centers↗
PubMed1988

Oligomeric structure of p21 ras proteins as determined by radiation inactivation.

Using radiation inactivation we determined that p21 ras proteins exhibit an oligomeric target size when assayed both structurally and functionally. Similar target sizes of p21 in ras-transformed cells and in purified preparations of the protein suggested that its structure is homo-oligomeric. p21 monomers were destroyed by radiation with the same target size as the GTP binding activity, indicating the occurrence of a tight association allowing energy transfer between the monomers. Irradiation in the presence of GTP, dithiothreitol, or EDTA did not change the target size. Normal (Gly12) and transforming (Lys12) forms of the protein exhibited similar target sizes. The homo-oligomeric structure suggests that p21 ras proteins do not conform to the structure of monomeric alpha subunits in classical G proteins (alpha beta gamma heterotrimers) and establishes similarities with other homo-oligomeric proteins (such as Escherichia coli CRP) which acquire the active conformation through subunit reorientation upon nucleotide binding.

Cell Line, Transformed↗
PubMed1987

Human retroviral sequences on the Y chromosome.

Novel endogenous human retroviral sequences were cloned by low-stringency hybridization, using the pol gene of endogenous human retrovirus 51-1. One clone, lambda NP-2, contained gag, pol, env, and long terminal repeat sequences related to the corresponding portions of clone 51-1 and the closely related full-length endogenous human retrovirus 4-1. The sequence of the env gene of NP-2 was 73% homologous to that of 4-1. Genomic Southern blots of male and female DNAs showed that NP-2 is located on the Y chromosome and that the Y chromosome also contains one other sequence closely related to the env and 3' flanking regions of NP-2. Conservation of flanking DNA suggests that the second Y chromosome copy of the NP-2 env sequence arose by gene duplication rather than provirus insertion.

Base Sequence↗
PubMed1986

Amplification and chromosomal dispersion of human endogenous retroviral sequences.

Endogenous retroviral sequences in humans have undergone amplification events involving both viral and flanking cellular sequences. We cloned members of an amplified family of full-length endogenous retroviral sequences. Genomic blotting, employing a flanking cellular DNA probe derived from a member of this family, revealed a similar array of reactive bands in both humans and chimpanzees, indicating that an amplification event involving retroviral and associated cellular DNA sequences occurred before the evolutionary separation of these two primates. Southern analyses of restricted somatic cell hybrid DNA preparations suggested that endogenous retroviral segments are widely dispersed in the human genome and that amplification and dispersion events may be linked.

Animals↗
PubMed1984

Distinctive termini characterize two families of human endogenous retroviral sequences.

Human DNA contains many copies of endogenous retroviral sequences. Characterization of molecular clones of these structures reveals the existence of two related families. One family consists of full-length (8.8 kilobases) proviral structures, with typical long terminal repeates (LTR's). The other family consists of structures, which contain only 4.1 kilobases of gag-pol sequences, bounded by a tandem array of imperfect repeats 72 to 76 base pairs in length. Typical LTR sequences that exist as solitary elements in the genome were cloned and characterized.

Base Sequence↗
PubMed1984

Conversational interactions between mothers and learning-disabled or nondisabled children during a problem-solving task.

This study focused on mother-child interactions during a problem-solving task to determine whether (a) mothers of learning-disabled children engage in conversational buffering to facilitate their child's participation in the task, and (b) whether learning-disabled children differ from nondisabled children in their use of language with their mothers. The results of this study provide some evidence that mothers of both learning-disabled and nondisabled children engage in conversational buffering, although there were few differences between the mothers of the learning-disabled and nondisabled children. Differences between learning-disabled and nondisabled children showed that the learning-disabled were more likely to agree with and less likely to disagree with their mothers than were the nondisabled children. These findings provide some evidence of maternal conversational buffering and suggest that learning-disabled children's previously reported unassertive conversational style in peer interactions extends to talk with their mothers.

Child↗
PubMed1983

Learning disabled boys' performance and self-assessments on physical fitness tests.

30 learning disabled boys drawn from a segregated private school for learning disabled children and 22 from a public school mainstream program and 22 nondisabled boys performed two physical fitness tests, sit-ups and shuttle run in one of two conditions. While normal achievers performed significantly better on one of the tests, there were no differences between the two samples of learning disabled youngsters. However, students' comparisons of their performance with classmates' indicated that learning disabled youngsters in the private school ranked themselves more favorably than those in mainstream classrooms.

Adolescent↗