Biological characterization of avian osteopetrosis

Keratan sulfate as a marker for medullary bone in fossil vertebrates

The ability to determine the sex of extinct dinosaurs by examining the bones they leave behind would revolutionize our understanding of their paleobiology; however, to date, definitive sex-specific skeletal traits remain elusive or controversial. Although living dinosaurs (i.e., extant birds) exhibit a sex-specific tissue called medullary bone that is unique to females, the confident identification of this tissue in non-avian archosaurs has proven a challenge. Tracing the evolution of medullary bone is complicated by existing variation of medullary bone tissues in living species; hypotheses that medullary bone structure or chemistry varied during its evolution; and a lack of studies aimed at distinguishing medullary bone from other types of endosteal tissues with which it shares microstructural and developmental characteristics, such as pathological tissues. A recent study attempted to capitalize on the molecular signature of medullary bone, which, in living birds, contains specific markers such as the sulfated glycosaminoglycan keratan sulfate, to support the proposed identification of medullary bone of a non-avian dinosaur specimen (Tyrannosaurus rex MOR 1125). Purported medullary bone samples of MOR 1125 reacted positively to histochemical analyses and the single pathological control tested (avian osteopetrosis) did not, suggesting the presence of keratan sulfate might serve to definitively discriminate these tissues for future studies. To further test these results, we sampled 20 avian bone pathologies of various etiologies (18 species), and several MB samples. Our new data universally support keratan sulfate as a reliable marker of medullary bone in birds. However, we also find that reactivity varies among pathological bone tissues, with reactivity in some pathologies indistinguishable from MB. In the current sample, some pathologies comprised of chondroid bone (often a major constituent of skeletal pathologies and developing fracture calluses in vertebrates) contain keratan sulfate. We note that beyond chemistry, chondroid bone shares many characteristics with medullary bone (fibrous matrix, numerous and large cell lacunae, potential endosteal origin, trabecular architecture) and medullary bone has even been considered by some to be a type of chondroid bone. Our results suggest that the presence of keratan sulfate is not exclusive evidence for MB, but rather must be used as one in a suite of criteria available for identifying medullary bone (and thus gravid females) in non-avian dinosaur specimens. Future studies should investigate whether there are definite chemical or microstructural differences between medullary bone and reactive chondroid bone that can discriminate these tissues.

Identifying medullary bone in extinct avemetatarsalians: challenges, implications and perspectives

Medullary bone (MB) is a sex-specific tissue produced by female birds during the laying cycle, and it is hypothesized to have arisen within Avemetatarsalia, possibly outside Avialae. Over the years, researchers have attempted to define a set of criteria from which to evaluate the nature of purported MB-like tissues recovered from fossil specimens. However, we argue that the prevalence, microstructural and chemical variability of MB in Neornithes is, as of yet, incompletely known and thus current diagnoses of MB do not capture the extent of variability that exists in modern birds. Based on recently published data and our own observations of MB distribution and structure using computed tomography and histochemistry, we attempt to advance the discourse on identifying MB in fossil specimens. We propose: (i) new insights into the phylogenetic breadth and structural diversity of MB within extant birds; (ii) a reevaluation and refinement of the most recently published list of criteria suggested for confidently identifying MB in the fossil record; (iii) reconsideration of some prior identifications of MB-like tissues in fossil specimens by taking into account the newly acquired data; and (iv) discussions on the challenges of characterizing MB in Neornithes with the goal of improving its diagnosis in extinct avemetatarsalians. This article is part of the theme issue 'Vertebrate palaeophysiology'.

Human-Aided Movement of Viral Disease and the Archaeology of Avian Osteopetrosis

The term avian osteopetrosis is used to describe alterations to the skeletal elements of several species of domestic bird, most typically the chicken, Gallus gallus domesticus (L. 1758). Such lesions are routinely identified in animal bones from archaeological sites due to their distinctive appearance, which is characterised by proliferative diaphyseal thickening. These lesions are relatively uncomplicated for specialists to differentially diagnose and are caused by a range of avian leucosis viruses in a series of subgroups. Only some avian leucosis viruses cause the development of such characteristic lesions in osteological tissue. Viraemia is necessary for the formation of skeletal pathology, and avian osteopetrosis lesions affect skeletal elements at different rates. Lesion expression differs by the age and sex of the infected individual, and environmental conditions have an impact on the prevalence of avian leucosis viruses in poultry flocks. These factors have implications for the ways in which diagnosed instances of avian osteopetrosis in archaeological assemblages are interpreted. By integrating veterinary research with archaeological evidence for the presence of avian leucosis viruses across Western Europe, this paper discusses the nature of these pathogens, outlines criteria for differential diagnosis, and offers a fresh perspective on the human-aided movement of animal disease in the past through investigation of the incidence and geographic distribution of avian osteopetrosis lesions from the first century BC to the post-medieval period.

Chemistry supports the identification of gender-specific reproductive tissue in Tyrannosaurus rex

Medullary bone (MB), an estrogen-dependent reproductive tissue present in extant gravid birds, is texturally, histologically and compositionally distinct from other bone types. Phylogenetic proximity led to the proposal that MB would be present in non-avian dinosaurs, and recent studies have used microscopic, morphological, and regional homologies to identify this reproductive tissue in both theropod and ornithischian dinosaurs. Here, we capitalize on the unique chemical and histological fingerprint of MB in birds to characterize, at the molecular level, MB in the non-avian theropod Tyrannosaurus rex (MOR 1125), and show that the retention of original molecular components in fossils allows deeper physiological and evolutionary questions to be addressed.

Differential expression and cellular localization of novel isoforms of the tendon biomarker tenomodulin

Tenomodulin (Tnmd, also called Tendin) is classified as a type II transmembrane glycoprotein and is highly expressed in developing as well as in mature tendons. Along with scleraxis (scx), Tnmd is a candidate marker gene for tenocytes. Its function is unknown, but it has been reported to have anti-angiogenic properties. Results in a knockout mouse model did not substantiate that claim. It has homology to chondromodulin-I. Single nucleotide polymorphisms of TNMD have been associated with obesity, macular degeneration, and Alzheimer's disease in patients. In the present study, three Tnmd isoforms with deduced molecular weights of 20.3 (isoform II), 25.4 (isoform III), and 37.1 (isoform I) kDa were proposed and verified by Western blot from cells with green fluorescent protein-linked, overexpressed constructs, tissue, and by qPCR of isoforms from human tissues and cultured cells. Overexpression of each Tnmd isoform followed by immunofluorescence imaging showed that isoforms I and II had perinuclear localization while isoform III was cytoplasmic. Results of qPCR demonstrated differential expression of each Tnmd isoform in patient's specimens taken from flexor carpi radialis, biceps brachii, and flexor digitorum profundus tendons. Knockdown of Tnmd increased the expression of both scleraxis (scx) and myostatin, indicating a potential negative feedback loop between Tnmd and its regulators. Knockdown of all Tnmd isoforms simultaneously also reduced tenocyte proliferation. I-TASSER protein three-dimensional conformation modeling predictions indicated each Tnmd isoform had different structures and potential functions: isoform 1, modeled as a cytosine methyltransferase; isoform 2, a SUMO-1-like SENP-1 protease; and isoform 3, an α-syntrophin, plextrin homology domain scaffolding protein. Further functional studies with each Tnmd isoform may help us to better understand regulation of tenocyte proliferation, tendon development, response to injury and strain, as well as mechanisms in tendinoses. These results may indicate novel therapeutic targets in specific tenomodulin isoforms as well as treatments for tendon diseases.

Natural infection and transmission of a retrovirus closely related to myeloblastosis-associated virus type 1 in egg-type chickens

Myeloblastosis-associated virus type 1 (MAV-1) is an exogenous avian retrovirus with oncogenic potential. MAV-1 was detected in young chicks hatching from eggs produced by an experimental genetic line of egg-type chickens. Transmissibility of MAV-1 had not been documented previously. This investigation was intended to partially characterize the virus involved and to study its transmissibility and oncogenicity in naturally and contact-infected chickens. Commercially produced white and brown layer pullets free of exogenous avian leukosis viruses were commingled at hatch with naturally MAV-1-infected chickens. The original MAV-1-infected chickens were discarded after approximately 8 wk, and the contact-exposed chickens were maintained in isolation for 36 wk. Young specific-pathogen-free (SPF) single comb white leghorn chickens were added to the group to study possible horizontal transmission of MAV-1 in young chickens. Upon weekly virus isolation attempts, MAV-1 was readily isolated from the contact-exposed white layers but not from the brown layers between 36 and 53 wk of age (18 wk in total). Three-week-old SPF chickens were readily infected with MAV-1 by contact as early as 1 wk postexposure. Throughout 22 hatches derived from the white and brown MAV-1-contact-exposed layers (between 36 and 53 wk of age), MAV-1 was frequently detected in the white layer progeny, whereas the virus was seldom isolated from the progeny produced by the brown layers during the same 18-wk period. MAV-1 induced a persistent infection in some of the SPF chickens that were exposed by contact at 3 wk of age. Gross tumors were not detected in any of the originally infected experimental chickens at 8 wk of age, in the contact-exposed brown or white layers at the termination of the study at 53 wks of age, or in the contact-exposed SPF chickens at the end of the study at 12 wk of age. Exogenous avian leukosis-related viruses may still be detected in egg-type chickens, emphasizing the importance of thorough screening before incorporation of experimental genetic material into commercial genetic lines of egg-type chickens.

Forensic investigation of a 1986 outbreak of osteopetrosis in commercial brown layers reveals a novel avian leukosis virus-related genome

Avian leukosis virus (ALV) is known to cause several neoplastic conditions in chickens, such as B-cell lymphomas, myelocytomas, erythroblastosis, and other types of neoplasia including osteopetrosis. We describe herein the identification of unique ALV-related proviral DNA sequences in an archived chicken bone affected with osteopetrosis. The osteopetrotic bone was obtained from an affected 46-week-old brown layer during an outbreak of osteopetrosis in Costa Rica in 1986. Analysis of proviral DNA in the 23-year-old osteopetrotic bone revealed unique exogenous ALV-related sequences that were named CR-1986 (Costa Rica, 1986). The 5' and 3' long terminal repeats (LTR) in the proviral DNA were identical to each other. The U3 regions in the LTRs were most similar to equivalent sequences in ALV-J, while U5 was identical to known endogenous ALV-E sequences. The predicted CR-1986 envelope protein was most similar to the envelope of myeloblastosis associated virus type 1 (MAV-1), although the percentage of amino acid sequence similarity to MAV-1 was low (90.4%). The variable and hypervariable regions of gp85 displayed several mutations compared to representative strains of ALV. The gp37 (transmembrane or TM) envelope protein showed three leucine to serine mutations that may represent important changes in the conformation of this protein, a finding that is currently being investigated. Several recombination events may have contributed to the emergence of CR-1986 because each analyzed segment was similar to a different ALV. CR-1986 may represent a unique ALV based on distinctive characteristics of its predicted envelope protein in comparison to previously reported ALVs.

Infectobesity: Obesity of Infectious Origin

The rapid increase in obesity and the associated health care costs have prompted a search for better approaches for its prevention and management. Such efforts may be facilitated by better understanding the etiology of obesity. Of the several etiological factors, infection, an unusual causative factor, has recently started receiving greater attention. In the last two decades, 10 adipogenic pathogens were reported, including human and nonhuman viruses, scrapie agents, bacteria, and gut microflora. Some of these pathogens are associated with human obesity, but their causative role in human obesity has not been established. This chapter presents information about the natural hosts, signs and symptoms, and pathogenesis of the adipogenic microorganisms. If relevant to humans, "Infectobesity" would be a relatively novel, yet extremely significant concept. A new perspective about the infectious etiology of obesity may stimulate additional research to assess the contribution of hitherto unknown pathogens to human obesity and possibly to prevent or treat obesity of infectious origins.

Retroviruses and bone diseases

In 1980, retroviruses were shown to be pathogenic to humans, and experimentation on animals involving retroviruses as causal agents of tumors and degenerative diseases of bone, brain, and lung gained interest. Osteopetrosis, which can be either inherited in rodents or retrovirally induced in cats, is exemplary. Because of replication cycle, retroviruses can be propagated not only as infectious agents but also as cellular genes. If a retroviral infection occurs in germ line cells, the viral genes, which must integrate in the host's DNA, can be passed on to the progeny and inherited as Mendelian characteristics. Therefore, a retroviral etiology could account for diseases that present either as sporadic (infectious) or familial (inherited), although they may be similar in their clinical manifestations. This approach led to the finding of 2 new human retroviruses: 1 in a patient who had sporadic benign osteopetrosis, and the other in a patient who had sporadic paraarticular osteoma. In both patients, the retrovirus was isolated from mononuclear blood cells, not from bone cells, because of the links between bone and the immune system. A systematic search for retroviruses in patients who have sporadic bone disease, which also may appear as inherited disease, has yet to be performed. Patients with sporadic disease could be managed by antiretroviral agents such as Zidovudin.

Sequences from myeloblastosis-associated virus MAV-2(O) and UR2AV involved in the formation of plaques and the induction of osteopetrosis, anemia, and ataxia

Recombinant viruses were made between myeloblastosis-associated virus MAV-2(O) and UR2AV to examine the relationship between regions of the MAV-2(O) genome and disease induction. The env-long terminal repeat (LTR) portion of MAV-2(O), when substituted into UR2AV, was sufficient to induce osteopetrosis identical to that caused by the parent MAV-2(O). When this region was reduced to the gp37 and LTR of MAV-2(O), osteopetrosis more severe than that caused by the parent virus was induced. Recombinant viruses that contained all or part of the MAV-2(O) env gene in the absence of the MAV-2(O) LTR induced a severe, chronic anemia and late-onset osteopetrosis, leading to the conclusion that the MAV-2(O) LTR, in addition to env, was required for rapid induction of osteopetrosis. A viral recombinant, pEU, which contained the gp85 segment of UR2AV substituted into MAV-2(O), induced an ataxia/cerebellar dysfunction not seen during infection with the other chimeric or parent viruses. In vitro studies of the parent and recombinant viruses demonstrated that the ability to form plaques on chicken embryo fibroblasts correlated with the presence of the MAV-2(O) gp37 and LTR except for construct pEU. When the viruses were inoculated into 10-day-old chickens, chimeras containing the env-LTR of gp37-LTR region of MAV-2(O) induced severe regenerative anemia similar to that induced by MAV-2(O). pEU was the exception, suggesting that the unique configuration of this chimera is responsible for its unusual pathogenic properties.

Persistent viral DNA synthesis associated with an avian osteopetrosis-inducing virus

Bone and red blood cell DNA was obtained from MAV-2(O) infected, osteopetrotic chickens and analyzed for the presence of integrated and unintegrated viral DNA. Results indicate that unintegrated MAV-2(O) DNA did not appear until after osteopetrotic lesions were well established. These observations lead us to conclude that, unlike some retroviral diseases, unintegrated viral DNA may not play a significant role in the pathogenesis of MAV-2(O) osteopetrosis. In addition, there was no evidence of a clonally derived tumor in the bone.

Pathogenic effect of osteopetrosis virus strain MAV-2(0) on guinea fowl pancreas

Osteopetrosis virus strain MAV-2(0) in guinea fowl pancreas induces early unspecific changes in separate acini and the development of neoplasia among apparently unaffected acinar tissue. The tumors were classified as serous and mucinous adenomas and adenocarcinomas, as well as poorly differentiated carcinomas. Foci of phenotypically altered acinar cells were observed in single experimental birds.

Induction of nephroblastoma by myeloblastosis-associated virus type 1: state of proviral DNAs in tumor cells

Myeloblastosis-associated virus type 1 (MAV1) derived from a molecular clone of infectious proviral DNA (B. Perbal, J. S. Lipsick, J. Svoboda, R. F. Silva, and M. A. Baluda, J. Virol. 56:240-244, 1985) was shown to specifically induce nephroblastoma in chickens and therefore belongs to the MAV-N class. We show that nephroblastomas are polyclonal tumors containing rearranged proviral genomes. Rearrangements occur preferentially in the gag-pol region of the MAV1 proviral genome, and similar rearrangements can be detected in well-developed independent tumors.

Osteoclasts in human osteopetrosis contain viral-nucleocapsid-like nuclear inclusions

We report the discovery of nuclear inclusions in the osteoclasts of three unrelated patients with benign osteopetrosis that resemble the osteoclast inclusions characteristic of Paget's disease of bone. These inclusions are morphologically and dimensionally identical to the nucleocapsids of a virus of the Paramyxoviridae family. Supporting a possible viral association with benign osteopetrosis in the observation of the presence of antigens of respiratory syncytial virus, measles virus, and/or mumps virus in the cells of all five patients whose paraffin-embedded bone specimens were tested. These included two patients whose osteoclasts contained nuclear inclusions. No patients with the malignant form of the disease have been studied. There is as yet no proof that a virus is causally related to human osteopetrosis even though a virus can produce an avian form of the disease.

Effect of Rous associated virus number 7 on lymphoid cells and tissues of the chicken

Infection of chicks or chick embryos with Rous associated virus number 7 (RAV-7) led to a decreased blastogenic response to Concanavalin A (Con A) by lymphocytes isolated from the spleen and thymus. Chicks infected with RAV-7 8 days after hatch manifested decreased Con A blastogenesis 5 weeks postinfection, while chicks infected in ovo at 10 days of incubation showed an unusual pattern of cell density dependent decreased blastogenesis two weeks post-hatch (three weeks post-infection). Histopathological examination of tissues from RAV-7 infected chicks revealed evidence of lymphoid organ involution and widespread lymphoproliferative lesions by 3 weeks of age. The combination of decreased in vitro lymphoid blastogenesis and in vivo lymphoproliferation suggests that RAV-7 interacts with lymphocytes in a fashion that has not previously been described in the chicken.

A sequential study of bone lesions caused by isolates of an avian osteopetrosis virus, MAV-2(0)

The pathogenesis of avian osteopetrosis caused by rapid and slow-onset isolates of myeloblastosis associated virus, MAV-2(0), was studied by inoculation of 10-day-old chick embryos with virus. Femur and calvarium were examined at 15, 17 and 19 days in ovo and 7 and 25 days after hatching by histologic and immunoperoxidase techniques. Femur and calvarium were also examined by electron microscopy at 17 and 19 days in ovo and at 7 days after hatching. Avian osteopetrotic bone lesions were characterized by exuberant periosteal proliferation; the time of onset varied with different virus isolates. In the femur virus was first associated with osteoprogenitor cells, then with osteoblasts and finally with osteocytes as the cells progressed through normal sequences of differentiation. The amount of virus produced by these cells did not correlate with onset of periosteal proliferation. Slow onset isolates provoked early virus production, but proliferative lesions did not develop until later. Conversely, the rapid onset isolate induced little early virus production, although lesions were present. Periosteal proliferation was associated with and preceded by perivascular edema and perivascular cell necrosis within the bone cortex following infection by all isolates. However, the rapid onset isolate caused more severe lesions than other isolates. These lesions included vascular thrombosis, capillary necrosis and focal bone necrosis. The relationship between early vascular lesions and late periosteal proliferation seen with the slow onset isolates is not as clear as with the rapid onset isolate. Calvarial bone, a representative flat bone, was found to have virus present, but at a level less than the femur. Vascular lesions were rarely seen in the calvarium and bone proliferation did not occur at this site.

Chicken strain G-B1 exhibits a relative resistance to avian osteopetrosis

The disease induced by the avian myeloblastosis associated virus MAV-2-O in the susceptible chicken strains Brown Leghorn (BLH) and Prague CB (CB) was compared with that induced in the resistant G-B1 strain. Osteopetrosis, stunting and lymphoid organ atrophy were more severe in BLH than in CB chickens. G-B1 animals remained superficially normal until the end of the experiment. In contrast to the other two strains, the histopathological changes were very mild and there was no sign of immunosuppression. After 4 months, however, nephroblastomas could be detected in more than 50 per cent of the infected G-B1 chickens. Similar tumors were also found in CB birds kept for up to 5 months. Antibodies against MAV-2-O specific viral proteins were detected in plasma from infected G-B1 chickens but the titers were less than in plasma of convalescent birds. Virus could be demonstrated in peripheral blood until the end of the experiment (at 8 weeks). Therefore the resistance of the G-B1 strain is due neither to a restriction at the receptor level nor the result of a humoral immune reaction, but represents a new type of relative resistance at the cellular level. From (CC X G-B1)F1 and (CC X G-B1)F2 crosses the resistant phenotype is determined by a single genetic factor. This gene is not linked to the major histocompatibility complex. There is also a sex-dependent factor, possibly hormonal, involved in the resistant phenotype.

Transformation of Brown Leghorn chicken embryo fibroblasts by avian myeloblastosis virus proviral DNA

Brown Leghorn chicken embryo fibroblasts were transfected with a mixture of avian myeloblastosis virus (AMV) and myeloblastosis-associated virus type 1 (MAV1) proviral DNA purified from lambda-Charon 4A recombinant clones. A transformed cell line (T1AM) able to grow without anchorage in semisolid medium was obtained. The presence of both proviral AMV and MAV sequences was detected in T1AM DNA by hybridization with v-myb- and MAV1-specific probes. Altered AMV and MAV1 proviral genomes were found in T1AM genome. Characterization of the RNA species expressed in transformed cells showed that in addition to a 2.5-kilobase (kb) putative subgenomic v-myb-specific RNA, three other myb-containing RNAs (9.4, 8.4, and 7.0 kb) were present in T1AM cells. No AMV genomic RNA was detected. Also, a new 5.0-kb MAV1-specific RNA species was expressed in transformed cells in addition to MAV1 genomic RNA species (7.8 kb). No infectious AMV virions are released by T1AM cells. Chicken embryo fibroblasts infected by T1AM-released virions contained and expressed all MAV1 sequences detected in T1AM transformed cells but did not express any transformation parameter. These results indicated that the presence of AMV proviral sequences in T1AM cells is responsible for their transformed phenotype.

Developmental and molecular aspects of nephroblastomas induced by avian myeloblastosis-associated virus 2-O

Avian myeloblastosis-associated virus-induced nephroblastomas are tumors consisting mainly of mesenchymal and epithelial renal elements with variable degrees of differentiation. The spatial distribution of developmental stages reflects a gradient of differentiation from less differential structures in the periphery towards more differentiated structures in the center of the lobules formed in the nephroblastomas. These heterogenic tumors contain discrete virus-cell DNA junction fragments and are therefore clonal outgrowths of a single transformed cell. These findings support the hypothesis that a mesenchymal, nephrogenic cell residual in the postembryonic kidney is the origin of the tumor, which grows by proliferation and differentiation of this target cell. All the tumors expressed higher levels of viral genomic and env messages than nontransformed tissue from the same kidney. A screening of oncogene expression with 13 different oncogenes revealed enhanced myc levels. There was, however, no rearrangement of c-myc or of the other oncogenes detected with EcoRI-digested tumor DNAs. This suggests that there is no insertion of viral elements adjacent to a c-myc. The levels of myc expression in embryonic kidneys were as high as in the tumors. Therefore, the enhanced myc expression in nephroblastomas is a reflection of the embryonic status of the tumor rather than a newly acquired function. This finding, plus the similarity of development and morphology of nephroblastomas and embryonic kidneys, suggests that the tumors arise as a result of a deficiency in a function which turns the embryonic status off.

Responses of chickens lacking or expressing endogenous avian leukosis virus genes to infection with exogenous virus

Line 0 chickens that lack endogenous viral (ev) genes and 15I5 X 7 chickens that carry and express ev genes were inoculated with the avian leukosis virus, RAV-1, at 1 day of age or as embryos, and maintained to 70 days of age. Comparable uninoculated controls were also kept. Most of the day-old inoculated chickens developed antibody by 70 days, but as expected, most of the embryo inoculated chickens remained viremic. Major differences in response between the lines were only noted after day-old inoculation. About 40% of Line 0 died of a specific nonneoplastic syndrome (NNS) while none of the 15I5 X 7 chickens did. Line 0 also developed neutralizing antibodies at a much earlier age than 15I5 X 7 and, consequently, virus was cleared from the serum much earlier. Day-old RAV-1 infection of Line 0 also lowered hematocrit more at 14 and 21 days of age than in 15I5 X 7 chickens. Body weight was clearly reduced at all ages in both lines of chickens by both day-old and embryo inoculation. After embryo inoculation, hematocrit was lowered in both lines of chickens between 28 and 42 days of age. Immune response to sheep red blood cells and Brucella abortus was only slightly and inconsistently reduced by inoculation of RAV-1 by both routes in both lines of chickens. It was concluded that the major influences of ev gene expression was to reduce the incidence of NNS and the neutralizing antibody response after RAV-1 inoculation of day-old chicks.

Pathogenesis of osteopetrosis induced by rapid and slow onset plaque isolates of an avian osteopetrosis virus

Examination of bone from chickens infected as 10-day-old embryos with isolates of an avian osteopetrosis virus revealed that MAV-2(O) plaque isolate 32/2/4 caused rapid bone growth, while MAV-2(O) plaque isolate 13 caused a mild form of bone growth. MAV-2(O) plaque isolate 32/2/4 caused anemia when injected into the 8-day-old hatched chick and bone growth in ovo when injected into the 4-day-old embryo. Passive administration of neutralizing antibody protected against MAV-2(O)-induced bone growth when antibody was given to the embryo 1 day after virus. Neutralizing antibody also protected against an acute anemia observed when normal and bursectomized chickens were given MAV-2(O) 32/2/4, but antibody did not prevent the appearance of a chronic anemia or osteopetrosis in bursectomized chickens. Repeated animal passage of a slow onset plaque isolate of MAV-2(O) caused the virus to progressively induce more severe bone growth and anemia.

A monoclonal antibody recognizes an epitope common to an avian-specific nuclear antigen and to cytokeratins

X3, a monoclonal antibody of unusual specificity, is described. This antibody reacts with one or more cytokeratin polypeptides and also reacts with an avian (chicken, quail) nuclear antigen that appears to be present in all cell types (chicken) tested, although with variable staining pattern and intensity. This antigen is distinct from the cytokeratins but does have an epitope in common with this class of proteins. It disappears from the nucleus during the early stages of cell division and reappears during anaphase as a granular cytoplasmic structure. In late telophase the antigen is relocated in the nucleus. This antigen, which we have designated as avian-specific nuclear antigen ( AVNA ), is not associated with chromatin or ribonucleoproteins. From immunoblotting experiments on chicken fibroblast nuclei, AVNA is probably a complex composed of one or several polypeptides, one of which has a molecular weight of approximately 60 kD. The proteins were identified as nuclear matrix proteins rather than pore complex-lamina proteins by immunoblotting experiments on the purified nuclear matrix of chicken erythrocytes. The major polypeptide had a molecular weight of 60 kD and the minor polypeptide a molecular weight of 69 kD.

Rapid induction of hypothyroidism by an avian leukosis virus

Infection of 10-day chicken embryos with an avian leukosis virus, RAV-7, resulted in hypothyroidism within 3 weeks posthatching. Histological examination of the thyroids from infected chickens showed an extensive infiltration of lymphoblastoid cells by 7 days posthatching. Areas resembling germinal centers were present in the thyroids of infected chickens by 3 weeks posthatching. Examination of circulating thyroid and pancreas hormones showed a significant reduction in T3 and T4 levels and a trend toward higher insulin levels after 16 days posthatching. T4 supplementation of RAV-7-infected chickens alleviated some aspects of the disease syndrome but did not abrogate all symptoms. Marked involution of both bursa and thymus glands was noted. RAV-7 had an RNA genome of 8.2 kilobases and a polypeptide composition characteristic of an avian leukosis virus. The hypothyroidism followed a dose response to RAV-7 infection.

Induction of angiosarcomas by ring-necked pheasant virus

Ring-necked pheasant virus, an avian leukosis virus, when injected into 10-day old chick embryos, caused angiosarcomas in the lungs of infected chickens within a short time. Angiosarcomas appeared as localized foci of proliferating cells in the lungs as early as 2 weeks posthatch, and by 6 weeks, the lungs of the infected chickens were frequently filled with tumor cells. Between 3 and 10 weeks of age, 80% of infected chickens died of the angiosarcomas; the 20% which lived 8 weeks or longer had small lung lesions and also developed fibrosarcomas, osteopetrosis, nephroblastoma, and lymphoid leukosis. Chickens with lung tumors were cyanotic, had breathing difficulty, and had packed cell volumes in excess of 50%. Other changes not necessarily correlated with lung tumor mass were stunting, lymphoid organ involution, and profuse diarrhea. Ring-necked pheasant virus has a genome RNA of 8.2 kb. This observation, together with its replication and disease induction after repeated plaque purification, suggests that ring-necked pheasant virus is a replication-competent avian retrovirus. Therefore, our results suggest that ring-necked pheasant virus is an avian leukosis virus which causes angiosarcomas rapidly at high incidence and which, therefore, may induce this type of tumor by a mechanism different from the induction of sarcomas by avian sarcoma viruses.

Rous-associated virus type 7 induces a syndrome in chickens characterized by stunting and obesity

Infection of 10-day-old chicken embryos with an avian retrovirus. Rous-associated virus type 7, resulted in a disease characterized by stunting and hyperlipidemia. By 20 days after hatch, infected chickens were smaller than hatchmates and developed ataxia and obesity over the next 30 days. Histological examinations of livers from infected chickens revealed a diffuse panlobular fatty infiltrate involving an accumulation of fat in microdroplets. Electron microscopic examinations of livers from infected chickens revealed hepatocytes with swollen mitochondria that lacked cristae. The thyroid and pancreas were infiltrated with lymphoblastoid cells by 1 week after hatch. An examination of the blood revealed a mild anemia, a frank lipemia, and high levels of uric acid. This syndrome induced by Rous-associated virus type 7 in chickens may be useful for elucidating the nature of several diseases, including that found in the fatty liver and kidney syndrome of chickens and that observed in a strain of obese chickens.

Electron microscopy of avian osteopetrosis induced by retrovirus MAV.2-O

Diaphyseal tibial bone of 12.5-13-day and 19-day-old embryos and 20-day-old hatched chicks infected with retrovirus MAV.2-O were examined by transmission electron microscopy. The viruses were associated with lining osteoblasts and osteocytes. Whereas the infection of the osteoblast layer seemed to be a transient stage, virus association with osteocytes was a constant and main ultrastructural feature. The viruses were found either in the osteoid or in the periosteocytic space of the bone lacunae. They arose from dense cytoplasmic areas located near the cell plasmalemma via a budding process. The newly budded virus particles often had a large tail or a fine stalk-like process lost in the extracellular space. The viruses underwent calcification by deposition of inorganic material and were incorporated in the bone trabeculae. No production of virus was observed in typical osteoclasts with well-differentiated ruffled borders. The viral-induced avian osteopetrosis seemed to result from increased bone deposition through stimulation of osteoblast and osteocyte activities, whereas osteoclastic bone resorption seemed to be undisturbed.

Collagen and noncollagen protein synthesis in chick limb bud cells infected with a virus that causes osteoblastoma

Infection of cultured stage 24 (day 4.5) chick limb cells (spot cultures) with myeloblastosis-associated virus 2-(osteo) (MAV-2(0)) produces cell density-dependent alterations of collagen and noncollagen protein synthesis over the course of 8 days in culture. Collagen synthesis in infected, low density cultures (100 k cells/spot) was maximal on day 4 and increased 12 fold compared with maximal values on days 5-6 for uninfected counterparts. The patterns of collagen synthesis were similar in uninfected or MAV-2(0)-infected cultures seeded at 200 (medium density) or 400 k cells (high density) per spot with peaks on days 5-6. Noncollagen protein synthesis (NCP) in infected, low density cultures was maximal on day 4 and increased 15.7 fold compared with maximal values on days 5-6 for uninfected counterparts. The patterns for NCP synthesis were similar for uninfected and MAV-2(0)-infected cultures seeded at medium density (peak on day 5). However, in MAV-2(0)-infected , high density cultures, NCP synthesis was maximal on day 4 and increased 2.9 fold compared with maximal values on days 5-6 for uninfected counterparts. Although kinetics of cell division and DNA synthesis were similar in uninfected and MAV-2(0)-infected limb bud cells, the virus may have diverse affects on different cell populations at the three cell densities employed in these experiments.

Pathology of chickens infected with avian nephoblastoma virus MAV-2(N)

A neophroblastoma-inducing myeloblastosis-associated virus, MAV-2(N), derived from avian myeloblastosis virus was characterized with respect to biochemical composition and avian pathogenesis. Purified fibroblast-grown virus contained the same size 35S ribonucleic acid and the same relative amounts of viral polypeptides as another myeloblastosis-associated virus inducing predominantly osteopetrosis MAV-2(O). Plaque-purified MAV-2(N) induced a 76 to 93% incidence of nephroblastoma and a 3 to 50% incidence of osteopetrosis in SPAFAS and line 15 x 7 chickens: the oncogenic spectrum and the onset of nephroblastoma varied with the line of chicken and the route of injection. Renal neoplasms were manifest in chickens older than 2 months and grew to a massive size. Furthermore, 29% of control chickens housed with MAV-2(N)-infected chickens demonstrated nephroblastoma. MAV-2(N)-infected chickens had growth rates and blood packed cell volumes comparable to those of uninfected chickens. Infected chickens 2 months of age had increased kidney, liver, and spleen weights; tumor-bearing chickens 3 to 4 months of age had increased liver, lung, brain, pancreas, and bone weights. The concentration of albumin was decreased and the concentration of gamma globulin was increased in the serum of MAV-2(N)-INFECTED CHICKENS. Analysis of the sera of nephroblastoma-bearing chickens for virus and antibody showed that three states existed: (i) high levels of neutralizing antibody, (ii) high levels of virus, and (iii) simultaneous presence of both at low levels. The pathological and virological features of MAV-2(N) which distinguish it from MAV-2(O) are discussed.

Characterization of anemia induced by avian osteopetrosis virus

Chickens infected intravenously at 8 days after hatching with an avian osteopetrosis virus developed a severe, progressive anemia in the absence of osteopetrosis. The anemia was characterized as a pancytopenia, in which erythrocytes, granulocytes, and thrombocytes decreased concomitantly. Serum bilirubin levels were normal, whereas erythrocytes from infected chickens demonstrated a slightly elevated osmotic fragility. A negative Coombs test indicated that there was no evidence for erythrocyte-bound antibody. Erythrocytes from infected animals had slightly decreased 51Cr-labeled erythrocyte survival time when compared with normal. Examination of marrow histological preparations, together with ferrokinetic studies with 59Fe, indicated that marrow failure occurred during the acute phase of the anemia. Circulating virus was present during the development and acute phases of the anemia, but disappeared during the recovery phase of the disease. Neutralizing antibody appeared after the disappearance of circulating virus. It is concluded that virus infection induced both marrow failure (aplastic crisis) and decreased erythrocyte survival.

Characterization of the immunosuppression accompanying virus-induced avian osteopetrosis

Infection of chickens with a myeloblastosis-associated virus which induced a high incidence of osteopetrosis was accompanied by immunosuppression. The immunosuppression was manifested in the following ways. The weight of the bursa, spleen, and thymus was depressed in infected chickens. Infected animals had a diminished capacity to form hemolytic plaques in a direct assay. Spleen cells from osteopetrotic animals did not respond to phytohemagglutinin, and the spleen and bursa had a decreased proportion of cells possessing surface immunoglobulin. Osteopetrotic animals failed to show an age-dependent increase in the proportion of cells demonstrating surface immunoglobulin that was observed in normal animals. However, several individual chickens with heavy osteopetrosis responded to antigenic stimulation in a normal fashion, indicating that although immunosuppression usually accompanies avian osteopetrosis, it may not contribute directly to abnormal bone proliferation.