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Biomedical subjects

P Tang

Publications and source records attributed to P Tang.

At least 127 records · Page 7Linked to original sources
PubMed1987

Analysis of mutation in human cells by using an Epstein-Barr virus shuttle system.

We developed highly sensitive shuttle vector systems for detection of mutations formed in human cells using autonomously replicating derivatives of Epstein-Barr virus (EBV). EBV vectors carrying the bacterial lacI gene as the target for mutation were established in human cells and later returned to Escherichia coli for rapid detection and analysis of lacI mutations. The majority of the clonal cell lines created by establishment of the lacI-EBV vector show spontaneous LacI- frequencies of less than 10(-5) and are suitable for studies of induced mutation. The ability to isolate clonal lines represents a major advantage of the EBV vectors over transiently replicating shuttle vectors (such as those derived from simian virus 40) for the study of mutation. The DNA sequence changes were determined for 61 lacI mutations induced by exposure of one of the cell lines to N-nitroso-N-methylurea. A total of 33 of 34 lacI nonsense mutations and 26 of 27 missense mutations involve G X C to A X T transitions. These data provide support for the mutational theory of cancer.

Cell Line↗
PubMed1987

Persistence of hepatitis B viral antigens in Culex quinquefasciatus.

Culex quinquefasciatus mosquitoes were fed on or inoculated with blood or serum positive for hepatitis B viral antigens and pools of mosquitoes were tested by radioimmunoassay daily for 3 weeks after exposure to detect the viral antigens. Hepatitis B surface antigen (HBsAg) was detectable up to 3 weeks, while hepatitis B e antigen (HBeAg) persisted only for 3 days in mosquitoes after feeding on hepatitis B viral antigens-positive blood. Mosquitoes inoculated with serum were HBsAg-positive for 3 weeks and HBeAg positive for 4 days after inoculation. These results suggest that biological multiplication of hepatitis B virus did not occur in these mosquitoes. The possibility of mechanical transmission of hepatitis B antigens by mosquitoes is discussed.

Animals↗
PubMed1986

Cytoskeletal changes during oogenesis and early development of Xenopus laevis.

The frog oocyte is well known for studies on the control of gene expression, but has been used much less in studies on the cytoskeleton. However, frog oocytes are very large single cells, whose cytoplasmic movements and asymmetries are fundamental to the correct development of the subsequent embryo. One particular example of asymmetrically distributed cytoplasm is germ plasm, thought to be important in the formation of the germ line. Data are presented that show that germ plasm is highly concentrated mass of cytoskeletal elements, which include tubulin, and an intermediate filament protein of molecular weight 55 X 10(3). The distribution of these molecules has been studied during oogenesis and during early post-fertilization development. The implications of these findings are discussed.

Animals↗
PubMed1979

Granular cell myoblastoma of the esophagus after irradiation for carcinoma.

Granular cell myoblastoma is an uncommon, usually benign tumor. Only 20 cases are reported in the esophagus. We describe a 65-year-old woman who developed a granular cell myoblastoma of the postericoid esophagus in the area of a squamous cell carcinoma successfully treated with irradiation. To our knowledge, this is the 21st reported case, and the only case occurring in the esophagus after irradiation for primary squamous cell carcinoma.

Aged↗
PubMed1977

Unusual events preceding hyperthyroidism with diffuse goiter.

Two unique patients with hyperthyroidism are presented here. A 48-year-old woman with a family history of Graves' disease was first evaluated and treated for a toxic adenoma with radioactive iodine. Three months later, she was again hyperthyroid, was found to have a diffuse thyromegaly, and was treated with radioactive iodine for the second time. This patient represents, to our knowledge, the first reported case of two sequential forms of endogenous hyperthyroidism. The second patient, a 64-year-old woman, had well-documented hypothyroidism that was presumably primary. She was admitted in thyroid storm and subsequently died. The autopsy disclosed characteristic changes in the thyroid of hyperthyroidism and a normal pituitary gland. The timing of the onset of Graves' disease with hyperthyroidism cannot be accurately determined.

Adenoma↗
PubMedDate not supplied

The radioulnar joints and forearm axis: surgeons' perspective.

Forearm injuries are common and can vary in complexity. The fractures are easily diagnosed, but the associated soft tissue injuries may not be as obvious. Treatment results are dependent not only on the fracture healing but on the return of normal relationships about the distal radioulnar joint, the interosseous membrane, and the proximal radioulnar joint. Alteration in any of these elements can result in permanent loss of forearm rotation and stability. Recent anatomic and biomechanical studies have increased our knowledge of these structures and their role in forearm function. The findings from these studies may lead to earlier repair of soft tissue injuries about the radioulnar joints and the interosseous membrane. Further follow-up of these procedures will be needed to validate their indications.

Biomechanical Phenomena↗
PubMedDate not supplied

Regulation of steroidogenic enzymes and a novel testicular RNA helicase.

Luteinizing hormone (LH) supports steroidogenesis and maintains testicular and ovarian function. Mediators of LH action exert homologous regulation of membrane receptors, steroidogenic enzymes and other regulatable genes of the Leydig cell (LC). Androgen and estrogen induced by LH could act through its cognate receptors in the LC to regulate gene expression. Although androgens are unquestionable essential for spermatogenesis and presumably exert their heterologous action through androgen receptors present in the Sertoli its regulatory mechanism in germinal cell maturation is far from clear. In contrast to physiological concentrations of gonadotropins which maintain the steroidogenic functions and LH and prolactin receptors in the gonads, high concentrations of gonadotropin (hCG) cause receptor down-regulation and desensitization of steroidogenic enzymes of the LCs in vivo (3beta-hydroxysteroid dehydrogenase types I and II, 17alpha-hydroxylase/17,20 lyase, and 17beta-hydroxysteroid dehydrogenase type III [17beta-HSD]). In addition, 17beta-HSD is regulated by compartmentalized endogenous glucose/ATP. The attenuation of steroidogenesis which results from receptor mediated activation by cognate hormone, but is independent of the subsequent phase of receptor down-regulation, is due to changes at the transcriptional level. Among the candidates affecting this regulation are active steroid metabolites (direct or indirect of steroids and other mediator(s) i.e. cAMP, putative transcription factors induced by LH action). Differential display assay revealed another gene which is transcriptionally regulated by gonadotropin termed GRTH (Gonadotropin Regulated Testicular Helicase). GRTH is a novel member of the DEAD-box family of RNA helicases, and is specifically expressed in LCs and meiotic LC of the testis. It is markedly up-regulated by hCG via cAMP-induced androgen formation in LCs at doses that cause down-regulation of receptors and steroidogenic enzymes. GRTH functions as a translational activator. Androgen produced by gonadotropin stimulation exerts intracrine/autocrine actions on GRTH, and also could influence transcription within the seminiferous tubule. GRTH may contribute to the control of steroidogenesis, including the restoration of down regulated cellular functions, and in the paracrine regulation of androgen dependent gene(s) involved in the meiotic process, and could thus have a crucial role in spermatogenesis.

Amino Acid Sequence↗