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Reticuloendotheliosis virus: A species in the group RETICULOENDOTHELIOSIS VIRUSES, AVIAN of the genus GAMMARETROVIRUS that causes a chronic neoplastic and a more acute immunosuppressive disease in fowl.Reticuloendotheliosis Viruses, Avian: A group of viruses in the genus GAMMARETROVIRUS comprising a few isolates from birds, with no known corresponding endogenous relatives.Reticuloendotheliosis, Avian: A group of pathologic syndromes found in avian species caused by RETICULOENDOTHELIOSIS VIRUS. The distinct syndromes include non-neoplastic runting, acute neoplastic disease, and chronic neoplastic disease. Humans and mammals appear resistant.Retroviridae: Family of RNA viruses that infects birds and mammals and encodes the enzyme reverse transcriptase. The family contains seven genera: DELTARETROVIRUS; LENTIVIRUS; RETROVIRUSES TYPE B, MAMMALIAN; ALPHARETROVIRUS; GAMMARETROVIRUS; RETROVIRUSES TYPE D; and SPUMAVIRUS. A key feature of retrovirus biology is the synthesis of a DNA copy of the genome which is integrated into cellular DNA. After integration it is sometimes not expressed but maintained in a latent state (PROVIRUSES).Fowlpox: A poxvirus infection of poultry and other birds characterized by the formation of wart-like nodules on the skin and diphtheritic necrotic masses (cankers) in the upper digestive and respiratory tracts.Alpharetrovirus: A genus of the family RETROVIRIDAE with type C morphology, that causes malignant and other diseases in wild birds and domestic fowl.Lymphatic Diseases: Diseases of LYMPH; LYMPH NODES; or LYMPHATIC VESSELS.Oncogene Proteins v-rel: Transforming proteins coded by rel oncogenes. The v-rel protein competes with rel-related proteins and probably transforms cells by acting as a dominant negative version of c-rel. This results in the induction of a broad range of leukemias and lymphomas.Oncogenic Viruses: Viruses that produce tumors.Chickens: Common name for the species Gallus gallus, the domestic fowl, in the family Phasianidae, order GALLIFORMES. It is descended from the red jungle fowl of SOUTHEAST ASIA.Helper Viruses: Viruses which enable defective viruses to replicate or to form a protein coat by complementing the missing gene function of the defective (satellite) virus. Helper and satellite may be of the same or different genus.Fowlpox virus: The type species of the genus AVIPOXVIRUS. It is the etiologic agent of FOWLPOX.Mardivirus: A genus in the family HERPESVIRIDAE, subfamily ALPHAHERPESVIRINAE, associated with malignancy in birds.DucksSatellite Viruses: Defective viruses which can multiply only by association with a helper virus which complements the defective gene. Satellite viruses may be associated with certain plant viruses, animal viruses, or bacteriophages. They differ from satellite RNA; (RNA, SATELLITE) in that satellite viruses encode their own coat protein.Marek Disease: A transmissible viral disease of birds caused by avian herpesvirus 2 (HERPESVIRUS 2, GALLID) and other MARDIVIRUS. There is lymphoid cell infiltration or lymphomatous tumor formation in the peripheral nerves and gonads, but may also involve visceral organs, skin, muscle, and the eye.Turkeys: Large woodland game BIRDS in the subfamily Meleagridinae, family Phasianidae, order GALLIFORMES. Formerly they were considered a distinct family, Melegrididae.Chick Embryo: The developmental entity of a fertilized chicken egg (ZYGOTE). The developmental process begins about 24 h before the egg is laid at the BLASTODISC, a small whitish spot on the surface of the EGG YOLK. After 21 days of incubation, the embryo is fully developed before hatching.Birds: Warm-blooded VERTEBRATES possessing FEATHERS and belonging to the class Aves.Herpesvirus 2, Gallid: The type species of the genus MARDIVIRUS in the family HERPESVIRIDAE. It is the etiologic agent of MAREK DISEASE, infecting domestic fowl and wild birds.Cell Transformation, Viral: An inheritable change in cells manifested by changes in cell division and growth and alterations in cell surface properties. It is induced by infection with a transforming virus.Oncogenes: Genes whose gain-of-function alterations lead to NEOPLASTIC CELL TRANSFORMATION. They include, for example, genes for activators or stimulators of CELL PROLIFERATION such as growth factors, growth factor receptors, protein kinases, signal transducers, nuclear phosphoproteins, and transcription factors. A prefix of "v-" before oncogene symbols indicates oncogenes captured and transmitted by RETROVIRUSES; the prefix "c-" before the gene symbol of an oncogene indicates it is the cellular homolog (PROTO-ONCOGENES) of a v-oncogene.Poultry Diseases: Diseases of birds which are raised as a source of meat or eggs for human consumption and are usually found in barnyards, hatcheries, etc. The concept is differentiated from BIRD DISEASES which is for diseases of birds not considered poultry and usually found in zoos, parks, and the wild.Avian Leukosis: A group of transmissible viral diseases of chickens and turkeys. Liver tumors are found in most forms, but tumors can be found elsewhere.Avian leukosis virus: The type species of ALPHARETROVIRUS producing latent or manifest lymphoid leukosis in fowl.RNA-Directed DNA Polymerase: An enzyme that synthesizes DNA on an RNA template. It is encoded by the pol gene of retroviruses and by certain retrovirus-like elements. EC 2.7.7.49.DNA, Viral: Deoxyribonucleic acid that makes up the genetic material of viruses.Virus Replication: The process of intracellular viral multiplication, consisting of the synthesis of PROTEINS; NUCLEIC ACIDS; and sometimes LIPIDS, and their assembly into a new infectious particle.Avian Sarcoma Viruses: Group of alpharetroviruses (ALPHARETROVIRUS) producing sarcomata and other tumors in chickens and other fowl and also in pigeons, ducks, and RATS.Genes, Viral: The functional hereditary units of VIRUSES.RNA, Viral: Ribonucleic acid that makes up the genetic material of viruses.Tumor Virus Infections: Infections produced by oncogenic viruses. The infections caused by DNA viruses are less numerous but more diverse than those caused by the RNA oncogenic viruses.Antigens, Viral: Substances elaborated by viruses that have antigenic activity.Viral Proteins: Proteins found in any species of virus.Nucleic Acid Hybridization: Widely used technique which exploits the ability of complementary sequences in single-stranded DNAs or RNAs to pair with each other to form a double helix. Hybridization can take place between two complimentary DNA sequences, between a single-stranded DNA and a complementary RNA, or between two RNA sequences. The technique is used to detect and isolate specific sequences, measure homology, or define other characteristics of one or both strands. (Kendrew, Encyclopedia of Molecular Biology, 1994, p503)TartratesCell Line: Established cell cultures that have the potential to propagate indefinitely.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Cell Transformation, Neoplastic: Cell changes manifested by escape from control mechanisms, increased growth potential, alterations in the cell surface, karyotypic abnormalities, morphological and biochemical deviations from the norm, and other attributes conferring the ability to invade, metastasize, and kill.Repetitive Sequences, Nucleic Acid: Sequences of DNA or RNA that occur in multiple copies. There are several types: INTERSPERSED REPETITIVE SEQUENCES are copies of transposable elements (DNA TRANSPOSABLE ELEMENTS or RETROELEMENTS) dispersed throughout the genome. TERMINAL REPEAT SEQUENCES flank both ends of another sequence, for example, the long terminal repeats (LTRs) on RETROVIRUSES. Variations may be direct repeats, those occurring in the same direction, or inverted repeats, those opposite to each other in direction. TANDEM REPEAT SEQUENCES are copies which lie adjacent to each other, direct or inverted (INVERTED REPEAT SEQUENCES).RNA Viruses: Viruses whose genetic material is RNA.Galliformes: An order of heavy-bodied, largely terrestrial BIRDS including pheasants, TURKEYS, grouse, QUAIL, and CHICKENS.Genetic Vectors: DNA molecules capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. Many are derived from PLASMIDS; BACTERIOPHAGES; or VIRUSES. They are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain GENETIC MARKERS to facilitate their selective recognition.Tritium