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Biomedical subjects

A Shih

Publications and source records attributed to A Shih.

At least 55 records · Page 3Linked to original sources
PubMed1991

Evolutionary implications of primate endogenous retroviruses.

Endogenous DNA sequences related to retroviruses are probably present in all primates. By using approaches based on the polymerase chain reaction, two separate studies have revealed the evolutionary history of some of these sequences. In the first study, a retrovirus-like reverse transcriptase (RT) sequence homologous to that of Baboon endogenous virus (BaEV) has been identified in both Old World monkeys and African apes, but not in humans or Asian apes. This RT sequence is highly conserved at the amino acid level, but not the nucleotide level, in the baboon, African green monkey, Java macaque, chimpanzee, and gorilla. The patterns of nucleotide substitution indicate functional conservation and suggest that this RT sequence was present in the primate germline before apes and Old World monkeys diverged about 30 million years ago. In the second study, a comparison of endogenous proviral DNAs and their adjacent sequences has been used to analyze the evolutionary history of three previously reported human endogenous retroviruses, HERV-E(4.14), HERV-R(3), and HERV-Ia. It is shown that these retroviruses have also been resident in the primate line since before the ape-Old World monkey divergence. The implications of the presence of functionally conserved RT genes in the germlines of primates, and the potential for using integration sites as tools for analyzing phylogenetic relationships among primates and their retroviruses, are discussed.

Amino Acid Sequence↗
PubMed1991

Copper loading of hearts increases postischemic reperfusion injury.

We studied the role of copper as a potential mediator of postischemic reperfusion injury in the isolated, perfused rat heart. Hearts were equilibrated with Krebs-Henseleit buffer for 10 minutes and then loaded with copper by way of perfusion with buffer containing 20 microM copper(II)-bis-histidial for 30 minutes. Control hearts were perfused with Krebs-Henseleit buffer alone during the loading period. Hearts than were washed with buffer for 10 minutes and subjected to 20 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Atomic absorption spectroscopy revealed a 67% increase in total copper content in loaded hearts by the end of the wash. By the end of the 30-minute period of reperfusion, control hearts demonstrated a 50-60% recovery of myocardial function as determined by peak systolic pressure, contractility, and heart rate. In contrast, copper-loaded hearts exhibited virtually no functional recovery within the 30-minute time period. Using salicylate as a probe, we determined that peak and duration of .OH formation appears to be increased in copper-loaded hearts during reperfusion. Furthermore, efflux of lactic dehydrogenase was significantly increased in copper-loaded hearts. Our results clearly demonstrate that increasing cardiac content of copper results in enhanced postischemic reperfusion injury associated with increased formation of .OH, thus suggesting an important catalytic role for this transition metal.

Analysis of Variance↗
PubMed1991

Primary structure and biological activity of human brain-derived neurotrophic factor.

Brain-derived neurotrophic factor (BDNF) is a 27-kDa basic protein of noncovalently linked 13.5-kD subunits related to nerve growth factor and is produced by the central nervous system (CNS). BDNF has been shown to promote the survival of neurons located in or directly connected with the CNS and is likely to function in adjusting the cell number within neuronal populations to the need of this projection field. Here we describe the primary structure of a human BDNF cDNA, the biological activities of pure recombinant human BDNF, and the tissue distribution of rat BDNF. BDNF mRNA can be found in some peripheral tissues as well as in the CNS, and recombinant human BDNF is a potent neurotrophic factor for primary peripheral sensory neurons.

Amino Acid Sequence↗
PubMed1991

Identification and characterization of a human homolog of the Schizosaccharomyces pombe ras-like gene YPT-3.

The Polymerase Chain Reaction was used to amplify ras and ras-like sequences from two human cDNA libraries. Members corresponding to each of the three major ras-subfamilies (ras, rho, and rab/YPT) were identified. The one homologous to rab/YPT, referred to here as YL8, appears to be the human homolog of the recently reported Schizosaccharomyces pombe YPT3 gene. The YL8 gene could encode a guanine nucleotide binding protein of 216 amino acids with about 70% amino acid sequence identity to S. pombe YPT3, and is transcriptionally active in a variety of human cell lines.

Amino Acid Sequence↗
PubMed1990

Primary structure and biological activity of a novel human neurotrophic factor.

During development, each tissue receives and maintains a number of specific neuronal projections that are adequate to sustain its function. The mechanism by which this intricate process occurs is not well understood, but it has been proposed that diffusible neurotrophic factors derived from the target tissue may be involved. Here we describe the identification of a novel human protein that is important for the growth, differentiation, and survival of primary sympathetic and placode-derived sensory neurons. This polypeptide, designated neuronotrophin-3, has a broad tissue distribution and is structurally related to both nerve growth factor and brain-derived neurotrophic factor. Its unique range of trophic and differentiation-inducing activities suggests that it is likely to play a wide role in defining the fate and function of nerve cells during development.

Amino Acid Sequence↗
PubMed1990

Characterization of four novel ras-like genes expressed in a human teratocarcinoma cell line.

A mixed-oligonucleotide probe was used to identify four ras-like coding sequences in a human teratocarcinoma cDNA library. Two of these sequences resembled the rho genes, one was closely related to H-, K-, and N-ras, and one shared only the four sequence domains that define the ras gene superfamily. Homologs of the four genes were found in genomic DNA from a variety of mammals and from chicken. The genes were transcriptionally active in a range of human cell types.

Amino Acid Sequence↗
PubMed1989

Detection of multiple, novel reverse transcriptase coding sequences in human nucleic acids: relation to primate retroviruses.

A variety of chemically synthesized oligonucleotides designed on the basis of amino acid and/or nucleotide sequence data were used to detect a large number of novel reverse transcriptase coding sequences in human and mouse DNAs. Procedures involving Southern blotting, library screening, and the polymerase chain reaction were all used to detect such sequences; the polymerase chain reaction was the most rapid and productive approach. In the polymerase chain reaction, oligonucleotide mixtures based on consensus sequence homologies to reverse transcriptase coding sequences and unique oligonucleotides containing perfect homology to the coding sequences of human T-cell leukemia virus types I and II were both effective in amplifying reverse transcriptase-related DNA. It is shown that human DNA contains a wide spectrum of retrovirus-related reverse transcriptase coding sequences, including some that are clearly related to human T-cell leukemia virus types I and II, some that are related to the L-1 family of long interspersed nucleotide sequences, and others that are related to previously described human endogenous proviral DNAs. In addition, human T-cell leukemia virus type I-related sequences appear to be transcribed in both normal human T cells and in a cell line derived from a human teratocarcinoma.

Amino Acid Sequence↗
PubMed1987

Cloned extrachromosomal circular DNA copies of the human transposable element THE-1 are related predominantly to a single type of family member.

The 2300 base-pair transposon-like human element, THE-1, has been identified in the extrachromosomal circular DNA of the established human cell line HeLa as a relatively homogeneous population of covalently closed 1900 base-pair molecules. THE-1, which has been classified tentatively as a retroviral-like transposable element (a retrotransposon), is present in the extrachromosomal circular DNA of African green monkey (BSC-1) and human lymphoblastoid (Jurkat) cell lines. The 1900 base-pair extrachromosomal elements isolated and cloned from HeLa cells (1) appear to contain only THE-1-specific nucleotide sequences, (2) are circularized versions of the linear chromosomal sequence, and (3) are related predominantly to a single, or single type of, family member.

Autoradiography↗
PubMed1978

Multiple autotransplantation of rat mammary induced by 7,12-dimethylbenz[a]anthracene: brief communication.

Mammary tumors induced in outbred Sprague-Dawley rats by 7,12-dimethylbenz]a]anthracene were excised, cut into 1- to 2-mm3 pieces, and then autotransplanted sc along the mammary line at six sites. Following an average period of 20--30 days, these autografts grew to approximately 2 cm in diameter in 32 of 48 rats (67%). Autografts in the other 33% of the rats remained dormant. Mammary tumors transplanted into allogeneic hosts failed to grow. Tumors derived from autotransplantation were indistinguishable from their primary tumors with respect to their histologic features, the nature of hormone dependency, the content of estrogen receptors, and their ability to incorporate [3H]leucine. Furthermore, autotransplanted tumors derived from a single primary tumor varied little with regard to the preceding parameters; thus they provided an opportunity for serial sampling of individual tumors for repeated morphologic and biochemical evaluations.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1977

Effect of intrauterine estriol on reproductive function in the rabbit.

The effect of intrauterine estriol on spontaneous ovulation, ovum fertilization, blastocyst development, and blastocyst implantation in rabbits has been investigated. Estriolreleasing intrauterine capsules constructed of biocompatible polymer were implanted in one uterine horn of adult New Zealand White female rabbits, while placebo-containing capsules were implanted into the contralateral horn. The animals were artificially inseminated and ovulated or mated to fertile bucks. The does were killed and their reproductive tracts were examined 54 hours, 6 days, and 10 days after ovulation-inducing injection or after coitus. The results indicate that intrauterine estriol released at a steady state rate of 1.25 mug/day effectively inhibits blastocyst development and implantation. This contraceptive effect was clearly local, since implantations in the contralateral,placebo-bearing horn were not inhibited. Furthermore, the same dose of estriol, when released systemically from a subcutaneously placed capsule, had no effect on implantation. Intrauterine estriol appeared also to have no effect on spontaneous ovulation or ovum fertilization.

Animals↗
PubMedDate not supplied

The effects of dietary zinc deficiency on voluntary alcohol drinking in rats.

The effects of dietary zinc deficiency on voluntary alcohol drinking in rats were examined in three separate experiments. Zinc-deficient rats showed a significantly greater voluntary alcohol intake as compared with the pair-fed controls. In the first experiment there were 14 male Sprague-Dawley rats with 7 controls and 7 who were begun on a zinc-deficient diet (below 2 ppm) at body weight 58-81 g. In the second experiment with 11 male Sprague-Dawley rats, the same diet was begun at 103-107 g. In the last experiment, 11 rats were begun at 120-199 g. Hair zinc measurements documented lower levels in the zinc-deficient rats after 6 weeks on the diet. The data indicate that a zinc-deficient state did increase voluntary alcohol intake in rats. In each experiment, the per cent alcohol consumed declined when a normal diet was given after the 6th week, and the difference was significant in experiments 1 and 3.

Alcohol Drinking↗