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At least 19 recordsLinked to original sources
PubMed2026

An ancient alpharetrovirus lineage in bats: Evolutionary insights and possible roles in reproduction.

Alpharetroviruses are an important group of pathogens known to cause leukemias and tumors, and were historically considered to be restricted to avian hosts. The identification of alpharetrovirus-like envelopes in bat genomes has hinted at a potentially wider host range, although their relations to modern alpharetroviruses and distribution remains unclear. Through a paleovirological screening of 818 vertebrate genomes we identified CHIRalphaEnv, a lineage that belongs firmly within alpharetroviruses, and emerged from a cross-class transmission from saurian hosts. We determine that CHIRalphaEnv envelope genes have been co-opted across bats on eight separate occasions between 43.8 and 18.9 million years ago and are preserved in most bat genomes screened. CHIRalphaEnv elements encode full-length envelope proteins and have been maintained under purifying selection, demonstrating multiple instances of exaptation by their bat hosts and a likely ubiquitous function. We observe high expression levels of CHIRalphaEnv envelopes in endometrium tissue from Carollia perspicillata, suggesting an involvement in reproductive function. We find CHIRalphaEnv sequence relatives in multiple mammalian clades (Afrotherians, rodents and bats), expanding the host range and extending origins of alpharetroviruses beyond 43 million years. We also propose the first mammalian co-opted Endogenous retrovirus (ERV) derived from an Alpharetrovirus envelope and explore the convergent functional recruitment of CHIRalphaEnv in hemochorial placentation in bats, elephant shrews and spiny mice. These findings highlight alpharetroviruses as a previously underappreciated source of functional exaptation in mammals.

Animals↗
PubMed2025

Diversity and evolutionary history of endogenous retroviruses in the genome of Manis pentadactyla.

Endogenous retroviruses (ERVs), remnants of ancient viral infections integrated into host genomes, serve as invaluable molecular fossils for studying viral evolution. In this study, we performed a genomic analysis of the Chinese pangolin (Manis pentadactyla), identifying novel full-length endogenous retroviruses, designated as Manis pentadactyla ERVs (MPERVs). MPERVs span three retroviral genera: Alpha-, Beta-, and Gamma-retroviruses. Using genomic screening and phylogenetic analysis, we classified MPERVs and reconstructed their evolutionary history, uncovering evidence of complex recombination events and cross-species transmission. Estimated insertion times for MPERVs range from very recent to 18.38 million years ago. MPERVs exhibit diverse structural features, notably including conserved retroviral domains and functional motifs and highlighting their preservation across extensive evolutionary periods. These findings shed light on the evolutionary dynamics of ERVs in Chinese pangolin and suggest the potential for expanded host ranges among certain retrovirus genera.IMPORTANCEEndogenous retroviruses are unique viruses distinguished by the fact that they are retained as part of the host genome after an exogenous retrovirus infects the host. The Chinese pangolin, as a host with a long independent evolutionary history, likely holds valuable insights in its genome regarding retrovirus endogenization and transmission. In this study, we identified the footprints of exogenous retroviruses from three different genera in the pangolin genome: Alpharetrovirus, Betaretrovirus, and Gammaretrovirus. Additionally, by calculating the integration times of the pangolin's endogenous retroviruses and analyzing the domains of the three main functional proteins (GAG, POL, and ENV), we found that the insertions are relatively young. This suggests that these endogenous retroviruses infected the Chinese pangolin long before their endogenization. This study represents the exploration of endogenous retroviruses in the Chinese pangolin genome, expanding our understanding of endogenous retroviruses in mammals. Furthermore, our findings provide new evidence for the phenomenon of the cross-species transmission of retroviruses prior to endogenization.

Endogenous Retroviruses↗
PubMed1975

Infectious DNA recovered from avian tumor-virus-producing cells.

A single treatment of chick embryo fibroblasts with DNA recovered from chick embryo fibroblasts productively infected and transformed with four different strains of RSV, or productively infected with two different strains of RAV, resulted in virus production and cell transformation (in the case of RSV) two or three passages after treatment (8-25 days). The virus recovered from cultures was phenotypically identical to that produced by the donor cells. No virus production nor cell transformation resulted from treatment of control cultures with DNA digested with DNAse. Infectious RSV-DNA was recovered from purified donor cell nuclei and was associated with the precipitable fraction of DNA prepared according to the method of Hirt (1967). It also sedimented with cellular DNA in density gradients, and with high molecular weight DNA (2-4 times 10-7 daltons) in sucrose gradients, which suggests that it is associated and may be integrated with chromosomal DNA. In some experiments, DNA fractions of lower molecular weight (down to 6 times 10-6 daltons) were also infectious. DNA from virus-producing RSV-transformed cells also gave rise to virus and Rous cells in cultures of fibroblasts from gs- embryos. However, the amount of DNA required for successful infection varied widely between experiments, and no reproducible dose-effect relationship was observed. The frequency of DNA-treated cells which produced virus remained low, even when the assay cultures were pretreated with 5-bromodeoxyuridine.

Alpharetrovirus↗
PubMed1976

Expression of viral proteins in mammalian cells transformed by avian sarcoma viruses.

The expression of viral proteins in nine lines of hamster and rat cells transformed by avian sarcoma viruses (ASV) was studied by indirect immunofluorescence with monospecific antisera to purified gp85 and p27 of AMV-B and a polyvalent antiserum to all the p proteins of this same virus. The lines of ASV-transformed cells were either low virus producers (VP) or inducible or non-inducible non producers (NP). Cytoplasmic expression of p proteins was observed in all the cell lines except the least inducible NP cell line, and cytoplasmic expression of gp85 in all the cell lines. The degree of expression varied widely with the lines and was not related to the class of permissiveness or inducibility. However, in the inducible NP class, the expression of p proteins and gp85 was higher in the most inducible cell lines. The data also suggest that the expression of the p proteins must be uncoordinate in at least some cell lines and must also be uncoordinate with the expression of gp85. In the VP cell lines and the most inducible NP lines, g85 and some p proteins other than p27 were also expressed on the cell membrane. The membrane expression of gp85 and the p proteins which were expressed appeared to be coordinate and to parallel the degree of cytoplasmic expression. In contrast, no, or a negligible expression of viral proteins was observed on the membrane of the least inducible and the non-inducible cell lines. These results suggest that there may exist translational and/or post-translational controls of the expression of viral proteins in the ASV-transformed mammalian cells and that the permissiveness and the inducibility of the cells may depend on the insertion of viral proteins in the cell membrane. The failure of p27 to insert in the cell membrane could account for the low permissiveness or the non-permissiveness of the cells.

Alpharetrovirus↗
PubMed1977

Adenylate cyclase activity and the cAMP level are not directly correlated with transformation by avian sarcoma viruses.

The adenylate cyclase activity was measured in chick embryo fibroblasts (CEF) infected with temperature-sensitive mutants (ts) of avian sarcoma virus (ASV). When CEF transformed with a (ts) mutant at 36 degrees C were incubated at the non-permissive temperature (41 degrees C), recovery from the low adenylate cyclase activity detectable in the transformed state was slower than the disappearance of signs of morphological transformation. After a downward shift of the temperature the activity decreased and this change was also slower than the alteration of cell morphology. The affinity of the enzyme system for ATP also changed after, and not during, morphological alteration. No significant difference was observed between the cAMP levels in ASV-transformed and non-infected CEF. These findings are consistent with the idea that adenylate cyclase is not involved in cell transformation and that the change in its activity is secondary to cell transformation.

Adenylyl Cyclases↗
PubMed1977

Avian retrovirus-induced surface antigens and their cross-reactivity with chemically-transformed cells and primary embryonic cells of Japanese quails.

By testing spleen cells from avian leukosis (ALV) and avian sarcoma virus (ASV)-injected Japanese quails in a microcytotoxicity assay against various target cells, we have demonstrated the existence of several target antigens. With non-transformed ALV-infected Japanese quail cells used as target cells, an avian retrovirus subgroup-specific destruction was obtained when spleen cells from animals infected with either avaian sarcoma or leukosis virus of the same subgroup were employed. This reaction is probably due to the virus envelope glycoproteins (Ve-gp) expressed on the cell surface. Apart from this subgroup-specific reaction, avian retrovirus group-specific destruction of ASV-transformed cells was demonstrated by means of effector cells immunized with ASV of a different subgroup. This reaction is restricted to transformed cells and not due to the virus envelope glycoprotein because the same effector cells are not cytotoxic to ALV-infected non-transformed cells but cytotoxic to sarcoma-virus-transformed cells which lack Ve-gp. Quail methylcholanthrene-tumor cells which show a transformation phenotype similar to that of ASV-transformed cells but which are free of detectable endogenous and exogenous retrovirus were also destroyed by the spleen cells from ASV tumorbearing animals. The same effector cells also exerted a weak cytotoxic effect on uninfected primary embryo cells but not to embryo cells after several passages.

Alpharetrovirus↗
PubMed1979

Neutralization of pseudotypes of vesicular stomatitis virus by sera from avian retrovirus-infected hosts.

We investigated the capacity of lymphocytes and sera from chickens bearing tumors induced by avian sarcoma viruses (ASV) to interact with phenotypically mixed particles of vesicular stomatitis virus (VSV) and ASV. Immune chicken sera were able to specifically neutralize such VSV pseudotypes. This ability could be absorbed out, however, on purified preparations of avian retroviruses, suggesting that reactivity was primarily against avian retrovirus enveloped components. Supernatant fluids containing phenotypically mixed particles were unable to stimulate division of lymphocytes of tumor-bearing hosts, an ability possessed by culture fluids containing native ASV particles. Polyacrylamide gel analysis was unable to resolve any distinct pseudotype protein, which was not present in either of the parental virus types. Treatment with crude preparations of ultraviolet (UV)-irradiated VSV pseudotype material did not afford immunity against subsequent challenge with live ASV.

Alpharetrovirus↗
PubMed1976

The effect of transformation-defective avian oncornavirus mutants on tumor antigen expression.

The recent isolation of conditional (temperature sensitive) and nonconditional transformation-defective mutants of avian sarcoma virus strains has facilitated the investigation of the effect of virus transformation on the cell's phenotype, e.g., with respect to morphology, growth pattern, or cell surface antigenicity. Special emphasis was laid on elucidating the correlation between transformed phenotype and tumor antigen expression. All of the tested nontransforming deletion mutants and the majority of the temperature-sensitive mutants were unable to induce tumor antigens in phenotypically untransformed cells. However, 3 temperature-sensitive mutants were found which were able to support the expression of tumor specific surface antigens even at restrictive temperature, when cells otherwise exhibited a normal phenotype. The theoretical and practical implications of this association between normal phenotype and tumor antigen expression are discussed.

Agglutination↗
PubMed1975

Chick muscle in tissue culture: the ubiquity of viral infection.

In chick skeletal muscle fibers cultured from embryos of commercially obtained "normal" eggs we have demonstrated numerous C-particles and large amounts of avian leucosis/sarcoma envelope antigen, especially when cultured in the presence of dinitrophenol. C-particles were present in t-tubules, which were possible intracellular viaducts of infection or dissemination and perhaps were the loci of receptors of viral invasion of the cytoplasm and sites of egress. The abundant lace-like membraneous proliferations, probably of t-tubules, usually had C-particles adjacent to or within them and perhaps were virus-provoked. Questioned is the validity of using cultured muscle, or extract, of embryos from ordinary chicken eggs for analysing normal biological phenomena--or conversely, is viral influence "normal" in chick development?

Alpharetrovirus↗