Biomedical subjects
Publications and source records attributed to A Burny.
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Cattle and sheep infected by Bovine Leukemia Virus (BLV) harbor complement-dependent cytotoxic IgG1 antibodies. These antibodies lyse BLV producing cells but are inactive against noncultured tumorous lymphocytes of animals with persistent lymphocytosis. The target structure in the cell membrane contains antigenic determinants of BLV gp 60. The level of cytotoxic activity increases with progression of the disease towards the tumor phase. Sheep vaccinated with inactivated BLV have no cytotoxic activity in the serum but seem to resist infectious BLV challenge. Such cytotoxic activities do not protect the host against tumor growth but strongly control viremia and thus limit BLV spread within bovine and ovine populations.
Bovine leukemia virus (BLV) single-stranded cDNA was used to study the distribution of DNA sequences in tissues (normal or malignant) from bovine, ovine and human origin. After recycling against normal bovine DNA, BLV (3H) cDNA hybridized with bovine enzootic tumor DNA but did not hybridize with normal bovine DNA. These results indicate that BLV is an exogenous RNA oncogenic virus and confirm that enzootic bovine leukosis (EBL) is an infectious disease. Proviral BLV sequences were also detected in buffy coat cells of animals in persistent lymphocytosis (PL) and carrying antibodies to BLV but no tumors. In animals at the tumor stage of EBL, the proviral sequences were found in buffy coat cells, in solid tumors (lymphosarcomas) and in organs infiltrated with tumoral lymphoid cells but not in apparently normal organs. No hybridization above background was observed between BLV (3H) cDNA and DNAs extracted from buffy coat cells and tumors corresponding to sporadic forms of bovine leukosis and some human leukemias and sarcomas.
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After microinjection of Xenopus laevis oocytes with RNA from avian myeloblastosis virus, viral structural proteins p27, p19, p15, and p12 are formed by a sequence of posttranslational cleavages of a high-molecular-weight precursor polypeptide. The 60-70S RNA aggregate or its 30-40S RNA subunits obtained by heat or formamide treatment possess the same ability to serve as template in X. laevis oocytes. The processing pattern of virus-specific precursor polypeptides is the same in X. laevis oocytes as in chick embryo fibroblasts infected with avian myeloblastosis virus, but the processing takes place at a much slower rate.
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The size of the polyadenylate segment of globin messenger RNA isolated from spleens of anaemic rabbits was estimated by comparison of its electrophoretic migration in polyacrylamide gels to that of synthetic poly(A) segments of known lengths. Conditions of enzymic degradation of mRNA with pancreatic ribonuclease and T1 ribonuclease were carefully established in order to ensure complete degradation of the heteropolymeric part of mRNA without affecting the polyadenylate sequence. The poly (A) segments of spleen globin mRNA were found to be 25-90 nucleotides long whilst those of peripheral blood reticulocytes from the same animals were only 10-30 residues long. Since spleen contains young erythroid cells and since anucleated blood reticulocytes constitute a statistically older population of the same cell line, these results support the idea that the poly(A) segment of mRNA shortens when the message ages.
Using polyacrylamide gel elution-electrophoresis in aqueous medium, highly purified rabbit globin mRNA can be fractionated into several populations of molecules differing by their mean poly(A) content. Both alpha and beta globin mRNA are heterogenous with respect to their electrophoretic mobilities. With the conditions used no separation of alpha and beta globin mRNA occurs during electrophoresis. From the specific radioactivity distribution in the different mRNA fractions one can conclude that the polyadenylate sequence at the 3' end of globin mRNA molecules becomes shorter with aging. This shortening occurs on alpha as well as beta, globin mRNAs and the extent of heterogeneity in poly(A) content is similar for both globin mRNAs. Furthermore, using two different methods of mRNA fractionation (polyacrylamide gel elution-electrophoresis and elution of poly (U)-Sepharose-bound mRNA at increasing temperatures) it is shown that old mRNA molecules differ from relatively young messages in their ability to direct cell-free globin synthesis. Modifications reducing template activity in vitro thus seem to take place during globin mRNA aging.
Short term cultures of bovine leukemic lymphocytes release virus particles with biochemical properties of RNA oncogenic viruses. These particles, tentatively called Bovine Leukemia Virus (BLV) have a high molecular weight-reverse transcriptase complex and a density averaging 1.155 g/ml in sucrose solutions. Molecular hybridizations between BLV-3H cDNA and several viral RNAs show that BLV is not related to Mason-Pfizer Monkey Virus (MPMV) Simian Sarcoma Associated Virus (SSV-1) Feline Leukemia Virus (FeLV) or Avian Myeloblastosis Virus (AMV). Rauscher Leukemia Virus (RLV) exhibits a slight but reproducible relatednesse to BLV. The high preference of BLV reverse transcriptase for Mg++ as the divalent cation suggests that BLV might be an atypical mammalian leukemogenic type C virus. Hybridization studies using BLV 3H cDNA as a probe suggest that the DNA of bovine leukemic cells contains viral sequences that cannot be detected in normal bovine DNA.
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