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Biomedical subjects

R Zhong

Publications and source records attributed to R Zhong.

151 records · Page 9Linked to original sources
PubMed1983

The primary structure and expression of four cloned human histone genes.

The complete nucleotide sequence of four human histone genes has been determined. Each gene codes for a core histone protein which is very homologous with the corresponding calf thymus of rat histones. The 5' and 3' flanking regions of the human histone genes contain previously identified concensus sequences: the TATA box, the GACTTC element; the CCAAT sequence; the 3' terminal dyad symmetry element thought to be involved in transcription termination; and a recently identified H2b specific upstream sequence. A putative H2a specific upstream sequence 5'-TTCTTGGACTCCTCTTTTC-3' is present approximately 40 base pairs upstream from the TATA box in the human H2a gene promoter. Nuclease S1 analysis of the human histone mRNAs encoded within each of these clones demonstrates that the mRNA terminii map to the expected positions relative to the known concensus sequences, and that the abundance of each mRNA is regulated during the HeLa cell cycle. Finally, in contrast to the H2b, H3 and H4 mRNAs encoded within clones pHh 4A/pHh4C, pHh5B and pHu4A, respectively, the H2a mRNA encoded by Hh5G is not present in human placental RNA.

Amino Acid Sequence↗
PubMedDate not supplied

Xenotransplantation of human decay accelerating factor transgenic porcine kidney to non-human primates: 4 years experience at a Canadian center.

From July 1999 to December 2002, a total of 27 baboons underwent transplantation with human decay accelerating factor (hDAF) transgenic porcine kidneys. The immunosuppressive protocol included combinations of 1 or more of the following immunosuppressive agents: cyclosporine, TPC, cyclosphophamide, methylprednisolone, GAS914 (a polymeric alpha-Gal), rabbit antithymocyte serum (RATS), and rapamycin derivative (RAD). The animals were followed up clinically with monitoring of renal function based on daily creatinine and urinary output. Histopathological examination of the tissue samples was performed after paraffin embedding. Electron microscopy was performed on occasion. All pathology was read blindly with a semiquantitative scoring method to assess the presence or absence of histological features of xenotransplant rejection. Mean survival time was 20.7 days (range, 4-75 days) with 15 animals dying of classic humoral rejection and 12 dying of complications unrelated to rejection. The most frequent complications were as follows: chronic diarrhea with malabsorption, bleeding diathesis, infections, and drug toxicity. Irrespective of the immunosuppressive regimen, a significant number of baboons (10) developed untreatable diarrhea and gastrointestinal bleeding. Samples of their gastrointestinal tracts showed evidence of varying degrees of necrotizing vasculitis with immunoglobulin (Ig)G,IgM, and fibrin deposition. The survival in pig-to-baboon kidney xenotransplantation continues to be limited by acute xenograft rejection and complications of immunosuppression. Although significantly increased survivals have been obtained, an ideal protocol has not yet been achieved. Efforts will continue in an attempt to develop a protocol with minimal complications and long-term survival beyond 90 days.

Animals↗
PubMedDate not supplied

Development of an XTT tetrazolium salt-based assay for detection of specific hyperthermia sensitizers in a high-flux screening programme.

It is now possible to search for new drugs using high-throughput screening of chemical libraries accumulated over the past few years. To detect potential new hyperthermia sensitizers, we are screening for chemical inhibitors of thermotolerance. For the screening of a large chemical library, a rapid and simple assay based on the XTT-tetrazolium salt with the addition of intermediate electron acceptor, phenazine methosulphate (PMS) as a promoter, was developed. It was found that the sensitivity of the XTT/PMS assay is sufficient for assessing thermal cell killing and thermotolerance, although it was highly dependent on cell number and type. When the formazan assay system was challenged with the bioflavonoid drug quercetin (up to 25mm) and validated against the clonogenic cell survival assay, significant decreases in thermotolerant cell viability were observed, directly reflecting inhibition of thermotolerance. Although short-term assays can, in some instances, underestimate overall cell killing, the dose dependency of inhibition of thermotolerance by quercetin recorded in this study by clonogenic and XTT/PMS assays was similar. Application of the XTT/PMS assay in chemical library screening was highly effective in differentiating potential thermotolerance inhibitors from both chemicals with lack of efficacy and from toxic compounds. Taken together, these results show that the XTT/PMS assay, when carried out under careful conditions, is well suited for primary high-flux screen of many thousands of compounds, thus opening up new areas for discovery of hyperthermia sensitizers.

3T3 Cells↗