Avian Oncoviruses Research Articles

Size and Genetic Content of Viral RNAs in Avian Oncovirus-Infected Cells

Viral complementary DNA (cDNA) sequences corresponding to the gag, pol, env, src, and c regions of the Rous sarcoma virus genome were selected by hybridizing viral cDNA to RNA from viruses that lack the env or src gene or to polyadenylic acid [poly(A)]-containing RNA fragments of different lengths and isolating either hybridized or unhybridized DNA. The specificities, genetic complexities, and map locations of the selected cDNA's were shown to be in good agreement with the size and map locations of the corresponding viral genes. Analyses of virus-specific RNA, using the specific cDNA's as molecular probes, demonstrated that oncovirus-infected cells contained genome-length (30-40S) RNA plus either one or two species of subgenome-length viral RNA. The size and genetic content of these RNAs varied, depending on the genetic makeup of the infecting virus, but in each case the smaller RNAs contained only sequences located near the 3' end of the viral genome. Three RNA species were detected in Schmidt-Ruppin Rous sarcoma virus-infected cells: 39S (genome-length) RNA; 28S RNA, with an apparent sequence of env-src-c-poly(A); and 21S RNA, with an apparent sequence of src-c-poly(A). Cells infected with the Bryan high-titer strain of Rous sarcoma virus, which lacks the env gene, contained genome-length (35S) RNA and 21S src-specific RNA, but not the 28S RNA species. Leukosis virus-infected cells contained two detectable RNA species: 35S (genome-length) RNA and 21S RNA, with apparent sequence env-c-poly(A). Since gag and pol sequences were detected only in genome-length RNAs, it seems likely that the full-length transcripts function as mRNA for these two genes. The 28S and 21S RNAs could be the active messengers for the env and src genes. Analyses of sequence homologies among nucleic acids of different avian oncoviruses demonstrated substantial similarities within most of the genetic regions of these viruses. However, the "common" region of Rous-associated virus-0, an endogenous virus, was found to differ significantly from that of the other viruses tested.

Continuous tissue culture cell lines derived from chemically induced tumors of Japanese quail

Several continuous tissue culture cell lines were established from methylcholanthrene-induced fibrosarcomas of Japanese quail. The lines consist either of fibroblastic elements, round refractile cells or polygonal cells. They show transformed characteristics in agar colony formation and hexose uptake, and most are tumorigenic. Their cloning efficiency in plastic dishes is not increased over that of normal quail embryo fibroblasts. The quail tumor cell lines do not produce endogenous avian oncoviruses and fail to complement the Bryan high titer strain of Rous sarcoma virus; those tested lack the p27 protein of avian oncoviruses. Most of the cell lines are susceptible to subgroup A avian sarcoma viruses, but are relatively resistant to viruses of subgroups C, E and F as compared to normal quail embryo fibroblasts.

Biological and biochemical studies on the inactivation of avian oncoviruses by ultraviolet irradiation

The effects of ultraviolet (uv) irradiation on transforming and replicating capacities of avian oncoviruses and on the synthesis of virus specific products after infection with irradiated virus were studied. Different strains of nondefective avian sarcoma viruses were inactivated at the same rate following single-hit kinetics. The 37% survival dose D 37 (1/ e) was 736 erg mm −2 on average. A comparison of the inactivation kinetics in a focus assay (transforming capacity) and an infectious center assay (replicating and transforming capacity) showed no partial inactivation of the virus genome; focus and infectious center formation were inactivated at the same rate. Similar results were obtained when the replicating capacity of the avian sarcoma virus was measured in a plaque assay; focus and plaque formation were inactivated at the same rate. No repair of the uv damage by either complementation or recombination with exogenous or endogenous avian leukosis virus could be demonstrated. The rates of inactivation of avian sarcoma virus assayed in focus and infectious center tests on chick embryo fibroblasts expressing or not expressing chicken helper factor, on chick embryo cells preinfected with RAV-1, and on Peking duck cells were identical. Nondefective avian sarcoma virus and deletion mutants of avian sarcoma virus defective for replication or transformation were inactivated at the same rate. Biochemical analysis of the DNA extracted from a Japanese quail tumor cell line (QT-6) 26 hr after infection with irradiated avian sarcoma virus strain B77 showed a decrease of total virus specific DNA and of full-length covalently closed circular (form I) viral DNA synthesis with increase of the uv dose. Virus-specific RNA synthesis, measured by hybridization of labeled RNA extracted from chicken embryo fibroblasts infected with irradiated virus to viral DNA, and particle production, assayed by uridine incorporation, were also inhibited with increasing uv dose. The inactivation rates for virus-specific DNA and RNA synthesis and for particle production were very similar, but lower than the rate for the loss of infectivity.

Endogenous leukosis viruses in the avian family phasianidae

Helper virus. activity for the defective Bryan high titer strain of Rous sarcoma virus (RSV) has been found in normal embryo fibroblast cultures of Ghighi, green, Mongolian, silver, and Swinhoe pheasants, and of Chinese quail and chukar. The helper viruses from Chinese quail and from Swinhoe pheasant were isolated from their respective RSV pseudotypes. Chinese quail, Ghighi, and golden pheasant cultures were also found to synthesize endogenous virus spontaneously. No such spontaneous production was seen with the other avian species investigated. The helper activity demonstrated in Chinese quail, chukar, Mongolian pheasant, and Swinhoe pheasant appears to specify envelope determinants which are different from those previously described. Viruses from Ghighi and silver pheasant have the G envelope, and those from green pheasant the F envelope specificity. The RSV pseudotype formed with Chinese quail virus shows a high plating efficiency on fibroblasts from mouse and European field vole. Chinese quail virus and Swinhoe pheasant virus also form plaques in chicken cells. Whether these pheasant viruses belong to established avian oncovirus groups, or whether they represent new ones, will have to be decided by immunological and biochemical studies now in progress.