Establishment and characterization of chicken embryo fibroblast clone LSCC-H32

Hi-C analysis of genomic contacts revealed karyotype abnormalities in chicken HD3 cell line

BACKGROUND

Karyotype abnormalities are frequent in immortalized continuous cell lines either transformed or derived from primary tumors. Chromosomal rearrangements can cause dramatic changes in gene expression and affect cellular phenotype and behavior during in vitro culture. Structural variations of chromosomes in many continuous mammalian cell lines are well documented, but chromosome aberrations in cell lines from other vertebrate models often remain understudied. The chicken LSCC-HD3 cell line (HD3), generated from erythroid precursors, was used as an avian model for erythroid differentiation and lineage-specific gene expression. However, karyotype abnormalities in the HD3 cell line were not assessed. In the present study, we applied high-throughput chromosome conformation capture to analyze 3D genome organization and to detect chromosome rearrangements in the HD3 cell line.

RESULTS

We obtained Hi-C maps of genomic interactions for the HD3 cell line and compared A/B compartments and topologically associating domains between HD3 and several other cell types. By analysis of contact patterns in the Hi-C maps of HD3 cells, we identified more than 25 interchromosomal translocations of regions ≥ 200 kb on both micro- and macrochromosomes. We classified most of the observed translocations as unbalanced, leading to the formation of heteromorphic chromosomes. In many cases of microchromosome rearrangements, an entire microchromosome together with other macro- and microchromosomes participated in the emergence of a derivative chromosome, resembling "chromosomal fusions'' between acrocentric microchromosomes. Intrachromosomal inversions, deletions and duplications were also detected in HD3 cells. Several of the identified simple and complex chromosomal rearrangements, such as between GGA2 and GGA1qter; GGA5, GGA4p and GGA7p; GGA4q, GGA6 and GGA19; and duplication of the sex chromosome GGAW, were confirmed by FISH.

CONCLUSIONS

In the erythroid progenitor HD3 cell line, in contrast to mature and immature erythrocytes, the genome is organized into distinct topologically associating domains. The HD3 cell line has a severely rearranged karyotype with most of the chromosomes engaged in translocations and can be used in studies of genome structure-function relationships. Hi-C proved to be a reliable tool for simultaneous assessment of the spatial genome organization and chromosomal aberrations in karyotypes of birds with a large number of microchromosomes.

Isolation of Ontario aquatic bird bornavirus 1 and characterization of its replication in immortalized avian cell lines

BACKGROUND

Aquatic bird bornavirus 1 (ABBV-1) has been associated with neurological diseases in wild waterfowls. In Canada, presence of ABBV-1 was demonstrated by RT-qPCR and immunohistochemistry in tissues of waterfowls with history of neurological disease and inflammation of the central and peripheral nervous tissue, although causation has not been proven by pathogenesis experiments, yet. To date, in vitro characterization of ABBV-1 is limited to isolation in primary duck embryo fibroblasts. The objectives of this study were to describe isolation of ABBV-1 in primary duck embryonic fibroblasts (DEF), and characterize replication in DEF and three immortalized avian fibroblast cell lines (duck CCL-141, quail QT-35, chicken DF-1) in order to evaluate cellular permissivity and identify suitable cell lines for routine virus propagation.

METHODS

The virus was sequenced, and phylogenetic analysis performed on a segment of the N gene coding region. Virus spread in cell cultures, viral RNA and protein production, and titres were evaluated at different passages using immunofluorescence, RT-qPCR, western blotting, and tissue culture dose 50% (TCID₅₀) assay, respectively.

RESULTS

The isolated ABBV-1 showed 97 and 99% identity to European ABBV-1 isolate AF-168 and North American ABBV-1 isolates 062-CQ and CG-N1489, and could infect and replicate in DEF, CCL-141, QT-35 and DF-1 cultures. Viral RNA was detected in all four cultures with highest levels observed in DEF and CCL-141, moderate in QT-35, and lowest in DF-1. N protein was detected in western blots from infected DEF, CCL-141 and QT-35 at moderate to high levels, but minimally in infected DF-1. Infectious titre was highest in DEF (between approximately 10⁵ to 10⁶ FFU / 10⁶ cells). Regarding immortalized cell lines, CCL-141 showed the highest titre between approximately 10⁴ to 10⁵ FFU / 10⁶ cells. DF-1 produced minimal infectious titre.

CONCLUSIONS

This study confirms the presence of ABBV-1 among waterfowl in Canada and reported additional in vitro characterization of this virus in different avian cell lines. ABBV-1 replicated to highest titre in DEF, followed by CCL-141 and QT-35, and poorly in DF-1. Our results showed that CCL-141 can be used instead of DEF for routine ABBV-1 production, if a lower titre is an acceptable trade-off for the simplicity of using immortalized cell line over primary culture.

The establishment of clonally derived chicken embryonic fibroblast cell line (CSC) with high transfection efficiency and ability as a feeder cell

This study established a single cloned chicken embryonic fibroblast (CEF) cell line. It solves the main problem of the instability of a cultured primary cell and its impact on the experiment. In this study, CEF pass through this crisis and formed a continuous cell line after subculture. We isolated single postcrisis CEF by a mouth pipette under a convert microscope then established a single cloned cell line named CSC-1-5 which passaged continuously from 96-well plates to 60 mm culture plates. CSC has a normal chicken diploid karyotype, no tumorigenicity, and a high G2/M phase cell ratio. We found that Fugene could mediate the transfection of CSCs efficiently; it was significantly improved compared with the primary cells. It could also promote the proliferation of chicken embryonic stem cell as a feeder layer.

The Periplasmic Trehalase Affects Type 1 Fimbria Production and Virulence of Extraintestinal Pathogenic Escherichia coli Strain MT78

Extraintestinal pathogenic Escherichia coli (ExPEC) is responsible for various infections outside the gastrointestinal tract in humans and other animals. ExPEC strain MT78 is invasive to various nonphagocytic cells and highly virulent in vivo To identify genes required for invasion of nonphagocytic cells by this strain, we applied signature-tagged mutagenesis to generate a library of mutants and tested them for invasion of avian fibroblasts. Mutants showing reduced cellular invasion included those with insertions in the fim operon, encoding type 1 fimbriae. Another attenuated mutant showed a disruption in the treA gene, which encodes a periplasmic trehalase. The substrate of TreA, trehalose, can be metabolized and used as a carbon source or can serve as an osmoprotectant under conditions of osmotic stress in E. coli K-12. We generated and characterized mutant MT78ΔtreA In contrast to the wild type, MT78ΔtreA was able to grow under osmotic stress caused by 0.6 M urea but not in minimal M9 medium with trehalose as the only carbon source. It presented decreased association and invasion of avian fibroblasts, decreased yeast agglutination titer, and impaired type 1 fimbria production. In a murine model of urinary tract infection, MT78ΔtreA was less able to colonize the bladder. All phenotypes were rescued in the complemented mutant. Our results show that the treA gene is needed for optimal production of type 1 fimbriae in ExPEC strain MT78 and that loss of treA significantly reduces its cell invasion capacity and colonization of the bladder in a murine model of urinary tract infection.

The virulence factor ychO has a pleiotropic action in an Avian Pathogenic Escherichia coli (APEC) strain

Background

Avian pathogenic Escherichia coli strains cause extraintestinal diseases in birds, leading to substantial economic losses to the poultry industry worldwide. Bacteria that invade cells can overcome the host humoral immune response, resulting in a higher pathogenicity potential. Invasins are members of a large family of outer membrane proteins that allow pathogen invasion into host cells by interacting with specific receptors on the cell surface.

Results

An in silico analysis of the genome of a septicemic APEC strain (SEPT362) demonstrated the presence of a putative invasin homologous to the ychO gene from E. coli str. K-12 substr. MG1655. In vitro and in vivo assays comparing a mutant strain carrying a null mutation of this gene, a complemented strain, and its counterpart wild-type strain showed that ychO plays a role in the pathogenicity of APEC strain SEPT362. In vitro assays demonstrated that the mutant strain exhibited significant decreases in bacterial adhesiveness and invasiveness in chicken cells and biofilm formation. In vivo assay indicated a decrease in pathogenicity of the mutant strain. Moreover, transcriptome analysis demonstrated that the ychO deletion affected the expression of 426 genes. Among the altered genes, 93.66 % were downregulated in the mutant, including membrane proteins and metabolism genes.

Conclusion

The results led us to propose that gene ychO contributes to the pathogenicity of APEC strain SEPT362 influencing, in a pleiotropic manner, many biological characteristics, such as adhesion and invasion of in vitro cultured cells, biofilm formation and motility, which could be due to the possible membrane location of this protein. All of these results suggest that the absence of gene ychO would influence the virulence of the APEC strain herein studied.

Indirect immunofluorescence assay for intra vitam diagnosis of avian bornavirus infection in psittacine birds

Different avian bornavirus (ABV) genotypes have recently been detected in psittacine birds with proventricular dilatation disease (PDD), an inflammatory fatal central and peripheral nervous system disorder. An indirect immunofluorescence assay (IIFA) for intra vitam demonstration of ABV-specific serum antibodies was established since reverse transcription-PCR (RT-PCR) assays may not detect all ABV variants.

Signature-tagged mutagenesis in a chicken infection model leads to the identification of a novel avian pathogenic Escherichia coli fimbrial adhesin

The extraintestinal pathogen, avian pathogenic E. coli (APEC), known to cause systemic infections in chickens, is responsible for large economic losses in the poultry industry worldwide. In order to identify genes involved in the early essential stages of pathogenesis, namely adhesion and colonization, Signature-tagged mutagenesis (STM) was applied to a previously established lung colonization model of infection by generating and screening a total of 1,800 mutants of an APEC strain IMT5155 (O2:K1:H5; Sequence type complex 95). The study led to the identification of new genes of interest, including two adhesins, one of which coded for a novel APEC fimbrial adhesin (Yqi) not described for its role in APEC pathogenesis to date. Its gene product has been temporarily designated ExPEC Adhesin I (EA/I) until the adhesin-specific receptor is identified. Deletion of the ExPEC adhesin I gene resulted in reduced colonization ability by APEC strain IMT5155 both in vitro and in vivo. Furthermore, complementation of the adhesin gene restored its ability to colonize epithelial cells in vitro. The ExPEC adhesin I protein was successfully expressed in vitro. Electron microscopy of an afimbriate strain E. coli AAEC189 over-expressed with the putative EA/I gene cluster revealed short fimbrial-like appendages protruding out of the bacterial outer membrane. We observed that this adhesin coding gene yqi is prevalent among extraintestinal pathogenic E. coli (ExPEC) isolates, including APEC (54.4%), uropathogenic E. coli (UPEC) (65.9%) and newborn meningitic E. coli (NMEC) (60.0%), and absent in all of the 153 intestinal pathogenic E. coli strains tested, thereby validating the designation of the adhesin as ExPEC Adhesin I. In addition, prevalence of EA/I was most frequently associated with the B2 group of the EcoR classification and ST95 complex of the multi locus sequence typing (MLST) scheme, with evidence of a positive selection within this highly pathogenic complex. This is the first report of the newly identified and functionally characterized ExPEC adhesin I and its significant role during APEC infection in chickens.

Generation and evaluation of a recombinant modified vaccinia virus Ankara vaccine for rabies

Modified vaccinia virus Ankara (MVA) has become a vaccine vector of choice for recombinant vaccine development. A MVA-based rabies vaccine would be advantageous for use as a vaccine for dogs (and wildlife), particularly if it proves innocuous and efficacious by the oral route. Here, the generation and immunological testing of a recombinant MVA expressing a rabies virus glycoprotein gene is described. In a murine model, higher dosages of recombinant MVA were needed to induce equivocal immune responses as with Vaccinia Copenhagen or Vaccinia Western Reserve recombinants, when administered by a parenteral route. The MVA recombinant was not immunogenic or efficacious when administered per os in naïve mice. The ability of the recombinant MVA to induce anamnestic responses in dogs and raccoons was also investigated. Recombinant MVA boosted humoral immune responses in these animals when administered peripherally, but not when administered orally.

Chicken embryo extract mitigates growth and morphological changes in a spontaneously immortalized chicken embryo fibroblast cell line

The SC-1 spontaneously immortalized chicken embryo fibroblast (CEF) cell line has been established recently. Although this cell line had been in culture for over 3 yr, its growth rate has remained lower than that of primary CEF cells, and the morphology has not been as uniform as observed in primary cells. In the present study, the SC-1 cell line was treated with chicken embryo extract (CEE) to determine whether growth rates could be increased and cell morphology enhanced. The CEE also was tested on primary CEF cells, another spontaneously immortalized CEF cell line (DF-1), and on 2 other nonvirally and nonchemically immortalized CEF cell lines (BCEFi and HCEFi). Results indicated that concentrations of CEE > or = 100 microg/mL inhibited growth of all cells tested. However, addition of 50 microg of CEE/mL enhanced the growth rate and improved the morphology of the SC-1 cells. Addition of CEE to the other immortal or primary CEF cells did not increase the growth rate or change their morphology. Analysis of mRNA expression revealed that SC-1 cells treated with 50 microg of CEE/mL had lower levels of the p16(INK4a) alternate reading frame sequence (ARF) and E2F-1 than untreated SC-1 cells. The increased growth rate and improved morphology of the SC-1 cells achieved with CEE treatment were retained following removal of CEE, and these improvements should aid in increasing the utility of the SC-1 cell line as a cellular/molecular reagent.

Glutamate regulates Oct-2 DNA-binding activity through α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors in cultured chick Bergmann glia cells

Ionotropic glutamate receptors in cerebellar Bergmann glial cells are linked to transcriptional regulation and, by these means, are thought to play an important role in plasticity, learning and memory and in several neuropathologies. Within the CNS, the transcription factors of the POU family bind their target DNA sequences after a growth factor-dependent phosphorylation-dephosphorylation cascade. Exposure of cultured Bergmann glial cells to glutamate leads to a time- and dose-dependent increase in Oct-2 DNA-binding activity. The use of specific pharmacological tools established the involvement of Ca2+-permeable alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors. Furthermore, the signaling cascade includes phosphatidyl inositol 3-kinase as well as protein kinase C activation. Interestingly, transcriptional as well as translational inhibitors abolish the glutamate effect, suggesting a transcriptional up-regulation of the oct-2 gene. These data demonstrate that Oct-2 expression is not restricted to neurons and further strengthen the notion that the glial glutamate receptors participate in the modulation of glutamatergic cerebellar neurotransmission.

From Weismann's theory to present day gerontology 1889-2003

From Weismann's theory to present day gerontology--Weismann's theory was based on the concept that through natural selection the division potential of somatic cells become finite thus limiting the regeneration of the soma and the life span of the organism. Indeed, the somatic cells of some animals have a finite division potential but what became apparent is that the implications for aging are more complex. Experiments showed that at each cell division the genetic information received by each daughter cell differs; cells are this way progressively modified through division creating a functional drift that is responsible in part for the continuous modifications going on in the organism from its very beginning to its extinction. Comparative biology showed that the finite or the infinite division potential of somatic cells has a complex connotation with developmental characteristics of the respective organism with implications for longevity that are far from being understood.

Truncated chicken interleukin-1beta with increased biologic activity

Chicken interleukin-1beta (ChIL-1beta) is synthesized as a precursor molecule that unlike its mammalian counterpart, lacks a typical caspase-1 cleavage site. Therefore, it was unclear if proteolytic cleavage of ChIL-1beta can occur and if cleavage might modulate the biologic activity of this cytokine. Using an avian indicator cell line that carries an NF-kappaB-regulated luciferase reporter gene, we established a sensitive and highly specific bioassay for ChIL-1beta. Experiments with a rabbit antiserum indicated that the NF-kappaB-stimulating activity in supernatants of lipopolysaccharide (LPS)-treated chicken HD-11 macrophages is largely due to IL-1beta and that proteolytic processing of natural and recombinant ChIL-1beta is not very efficient. Functional analyses further revealed that cDNAs for either full-length or N-terminally truncated chicken ChIL-1beta yielded active cytokine. A truncated molecule that closely resembled putative mature ChIL-1beta exhibited more than 100-fold enhanced biologic activity after expression in mammalian cells, indicating that precursor cleavage is indeed of critical importance for maximal activity.

Sequence comparison of avian interferon regulatory factors and identification of the avian CEC-32 cell as a quail cell line

Interferon (IFN) regulatory factor-1 (IRF-1) is a well-characterized member of the IRF family. Previously, we have cloned cDNA of several members of the chicken IRF (ChIRF) family and studied the function of ChIRF-1 in the avian cell line CEC-32. The IRF-1 proteins from primary chicken embryo fibroblasts (CEF) and CEC-32 cells differed in their electrophoretic mobility. To characterize the different forms of IRF-1 in avian cells, we compared the sequences of IRF-1 cDNA from CEC-32 cells, primary CEF, and quail fibroblasts (QEF). The deduced amino acid sequences of IRF-1 cDNA from chicken and quail show high similarity. Comparison of genomic sequences of IRF-1 and IFN consensus sequence binding protein (ICSBP) also confirm the relatedness of the members of the IRF family in quail and chicken. Based on these data, it is concluded that the avian fibroblast cell line CEC-32 is derived from quail. This conclusion is further supported by deoxynucleotide sequence comparison of a DNA fragment in an avian MHC class II gene and by fluorescence in situ hybridization (FISH) using the vertebrate telomeric (TTAGGG) repeat. Chromosome morphology and the lack of interstitial hybridization signals in macrochromosomes suggest that the CEC-32 cell line has probably been derived from Japanese quail.

Novel chicken CXC and CC chemokines

Upon stimulation with lipopolysaccharide (LPS) the chicken macrophage cell line HD-11 secretes factors with cytokine activity. To characterize these molecules, representational difference analysis with RNA of LPS-induced and uninduced HD-11 cells was performed. Two cDNA clones were isolated that code for polypeptides with structural features of chemokines. cDNA K60 codes for a novel CXC chemokine of 104 residues including a putative signal peptide of 20 amino acids at the N-terminus. It is 67% identical to the previously cloned chicken chemokine 9E3/CEF4. K60 exhibits a similar degree of sequence identity to human interleukin 8 and other related CXC chemokines (about 50%), rendering straight-forward predictions of its biological properties difficult. cDNA K203 codes for a novel CC chemokine of 89 amino acids including a putative N-terminal signal peptide of 21 residues. It is 43% identical to a previously characterized chicken protein with homology to mammalian macrophage inflammatory protein 1beta (MIP-1beta). K203 exhibits about 50% sequence identity to human MIP-1beta and other related CC chemokines.

Recombinant duck interferon gamma inhibits duck hepatitis B virus replication in primary hepatocytes

Interferon gamma (IFN-gamma), which has been cloned in several mammalian species and recently in birds, plays a critical role in modulating immune system function. IFN-gamma and tumor necrosis factor alpha (TNF-alpha) have been shown to be crucial in the pathogenesis of viral hepatitis and in the transient disappearance of hepatitis B virus (HBV) from the liver after adoptive transfer of HBV-specific cytotoxic T lymphocytes into HBV-transgenic mice. Similar studies in the natural animal hosts of related hepadnaviruses have been limited because the corresponding probes and recombinant cytokines were not available. For this reason, we initiated studies to clone and characterize cytokines from the duck, the natural host of the duck hepatitis B virus (DHBV). We describe here the cDNA cloning and initial characterization of the IFN-gamma homologue of ducks (DuIFN-gamma). The DuIFN-gamma cDNA codes for a predicted mature protein of 145 amino acids with a molecular mass of 16.6 kDa. The precursor protein has 67% identity with the previously cloned chicken IFN-gamma and 21 to 34% identity with mammalian IFN-gamma. Recombinant DuIFN-gamma induces the transcription of several IFN-inducible genes including IFN regulatory factor 1 and guanylate-binding protein, and it exhibits antiviral activity that protects duck cells from vesicular stomatitis virus-mediated lysis. Importantly, treatment of primary duck hepatocytes with recombinant DuIFN-gamma inhibits DHBV replication in a dose-dependent fashion. Time course analysis revealed that IFN-gamma treatment does not affect initial covalently closed circular DNA (cccDNA) conversion but inhibits the synthesis of progeny cccDNA by amplification.

Salmonellosis in relation to chlamydiosis and pox and Salmonella infections in captive falcons in the United Arab Emirates

During the spring of 1995, 1996 and 1997 following tests on six peregrine falcons (Falco peregrinus) and two gyr falcons (Falco rusticolus), Salmonella typhimurium was isolated from liver, spleen and small intestines. Four of the falcons (two peregrines and two gyrs) had also contracted Chlamydia infection, three peregrines a pox infection and one peregrine a Herpesvirus infection. It is believed that this dual infection was fatal for these birds. The disease was marked by anorexia, dehydration and green-coloured droppings. Necropsy of all falcons revealed discolouration of the liver and enlargement of liver and spleen. Miliary necrosis was detected in all livers. A total of 12 salmonella serovars, including S. typhimurium, were cultured from faeces of 48 falcons which showed no clinical signs.

Overexpression of chicken interferon regulatory factor-1 (Ch-IRF-1) induces constitutive expression of MHC class I antigens but does not confer virus resistance to a permanent chicken fibroblast cell line

The chicken fibroblast cell line C32 has been transfected with the chicken homolog (Ch-IRF-1) of the mammalian transcription factor IRF-1. Stable transfectants were generated, constitutively overexpressing Ch-IRF-1 mRNA and protein. Cells overexpressing Ch-IRF-1 showed enhanced constitutive expression of MHC class I (B-F, beta-microglobulin) antigens. With increasing number of passages cells with normal B-F IV surface antigen expression accumulated. In the revertants, the amount of Ch-IRF-1 mRNA was reduced. Overexpression of Ch-IRF-1 had no effect on the constitutive expression and the induction by chicken interferon type-I and type-II (Ch-IFN) of guanylate-binding protein (GBP). Susceptibility to vesicular stomatitis virus, sindbis virus, Newcastle disease virus and vaccinia virus was not altered by overexpression of Ch-IRF-1. An antiviral state could be induced against all viruses tested by similar amounts of Ch-IFN type I in clone 20-18 expressing Ch-IRF-1 and cells transfected with empty vector.

The DF-1 chicken fibroblast cell line: transformation induced by diverse oncogenes and cell death resulting from infection by avian leukosis viruses

DF-1 is a continuous cell line of chicken embryo fibroblasts. The cells are free of endogenous sequences related to avian sarcoma and leukosis viruses and have normal fibroblastic morphology. DF-1 cells support the replication of avian retroviruses; diverse oncogenes induce foci of oncogenic transformation on monolayers of DF-1, and avian leukosis viruses of envelope subgroups B, D, and C induce cell death and form plaques. The new cell line will greatly facilitate studies on oncogenic transformation and cell killing by avian viruses.

Expression and functional characterization of recombinant chicken interferon-gamma

A cDNA encoding chicken interferon-gamma (chIFN-gamma) was cloned from a CD4+ T-cell hybridoma by reverse transcription-polymerase chain reaction (RT-PCR) and expressed in Escherichia coli, COS- and CEC-32 fibroblast cell lines. In general, recombinant chicken IFN-gamma (rchIFN-gamma) expressed in the COS- and CEC-32 cell lines showed high bioactivity in vitro. The kinetics of IFN-gamma gene expression were examined in concanavalin A (Con A)-activated spleen lymphocytes by Northern blot and RT-PCR. IFN-gamma mRNA was detected as early as 30 min after Con A activation, reached peak expression at 2 h and then decreased starting at 4 h post Con A activation. A rabbit serum made to a synthetic peptide of IFN-gamma immunoprecipitated a 60 kDa E. coli maltose-binding fusion protein of recombinant IFN-gamma (MBP-IFN) and a 26-27 kDa secreted protein from COS cells and Con A-activated spleen cells. IFN-gamma inhibited vesicular stomatitis virus (VSV) mediated cytotoxicity of chicken embryonic fibroblast (CEF) cells and upregulated the expression of many macrophage cell surface antigens, including class I and class II major histocompatibility complex (MHC) proteins. These results show that chicken IFN-gamma possesses anti-viral activity and immunoregulates macrophage activities.

Chicken vigilin gene: a distinctive pattern of hypersensitive sites is characteristic for its transcriptional activity

Vigilin, a multidomain hn-ribonucleo-K-homologous protein, is part of a ribonucleoprotein complex with cognate tRNA and is found in both the nucleus and the cytoplasm. In an approach to identify genomic regions involved in regulation of the chicken vigilin gene, we carried out transfection studies with a reporter gene in suitable chicken cells. After including a distantly positioned 5'-sequence in the construct, we observed a 10.5-fold increase in luciferase (EC 1. 13.12.7) expression compared with basal promoter activity. Accordingly, chromatin analysis of freshly isolated embryonic tendon fibroblasts with high levels of vigilin mRNA expression shows a DNase-I-hypersensitive site (DHS1) localized 2.2 kb upstream of the transcriptional start site. Similarly, phytohaemagglutinin-stimulated lymphocytes with a 4-fold elevated expression of vigilin mRNA compared with resting lymphocytes also exhibited this unique DHS, having switched from that found at 3.3 kb (DHS2) in resting lymphocytes. Furthermore, using gel-retardation experiments with DNA representing either DHS1 or DHS2, a specific interaction with chicken nuclear extracts was seen.

Cloning of chicken interferon regulatory factor-2 (IRF-2) cDNA: expression and mapping of the IRF-2 gene

A cDNA clone encoding a member of the avian interferon regulatory factor (IRF) family homologous to mammalian IRF-2 was isolated from cDNA library from poly[rI:rC]-induced chicken embryo fibroblasts (CEF). The deduced amino acid sequence shows a characteristic DNA binding domain of 124 amino acids at the amino-terminal end with 96.8% identity to human and 96% to mouse IRF-2. Identities in the C-terminal part are 77.5% and 77%, respectively. Identity to all other known members of the chicken IRF (Ch-IRF) family is distinctly lower. In C32 cells, an IRF-2 mRNA of 2.4 kb is constitutively expressed in very low amounts but is inducible by Ch-IFN in the absence or presence of cycloheximide. The Ch-IRF-2 gene is a single copy gene and was mapped by fluorescence in situ hybridization to the long arm of chromosome 4.

Biological properties of recombinant chicken interferon-gamma

Supernatants of the chicken T cell line 855 contain antiviral and macrophage activating factor activity and strongly activate transcription of the guanylate binding protein (GBP) gene in chicken cells. To characterize the cytokine responsible for the GBP-inducing activity, we chose a cDNA expression cloning strategy in COS cells. Sequencing a positive clone revealed that it encode chicken interferon-gamma (ChIFN-gamma). Histidine-tagged ChIFN-gamma was expressed in Escherichia coli and purified by nickel chelate affinity chromatography. ChIFN-gamma from COS cells and E. coli both potently induced GBP RNA synthesis but were rather poor antiviral agents. In macrophages, recombinant ChIFN-strongly stimulated secretion of nitric oxide and enhanced expression of major histocompatibility complex class II antigen. A rabbit antiserum to E. coli derived ChIFN-gamma effectively neutralized the macrophage-activating factor activity secreted by concanavalin A-induced spleen cells and various T cell lines, suggesting that IFN-gamma is the major macrophage-activating factor of the chicken.

Chicken guanylate-binding protein. Conservation of GTPase activity and induction by cytokines

To gain further insights into the cytokine network of birds, we used polymerase chain reaction technology to clone a cDNA that codes for a chicken homolog of the interferon-induced guanylate-binding proteins (GBPs). In its N-terminal moiety, the 64-kDa chicken GBP contains two sequence blocks of 100 and 19 amino acids, respectively, that are about 70% identical to mammalian GBPs. The first region includes two motifs of the canonical GTP-binding consensus element. The other parts of chicken GBP are poorly conserved, except for a CAAX motif at the extreme C terminus which might signal isoprenylation. Like mammalian GBPs, recombinant chicken GBP specifically bound to agarose-immobilized guanine nucleotides and hydrolyzed GTP to both GDP and GMP. Regulation by interferons was also conserved: chicken GBP RNA was barely detectable in uninduced chicken cells. Low GBP RNA levels were found in cells treated with type I interferon, whereas very high levels were observed in cells treated with supernatant of a chicken T cell line that secretes a gamma-interferon-like activity. Together with recent phylogenetic studies of interferon genes, these results suggest that in spite of low sequence conservation, the various components of the avian interferon system are functionally well conserved.

Chicken interferon consensus sequence-binding protein (ICSBP) and interferon regulatory factor (IRF) 1 genes reveal evolutionary conservation in the IRF gene family

Members of the IRF family mediate transcriptional responses to interferons (IFNs) and to virus infection. So far, proteins of this family have been studied only among mammalian species. Here we report the isolation of cDNA clones encoding two members of this family from chicken, interferon consensus sequence-binding protein (ICSBP) and IRF-1. The predicted chicken ICSBP and IRF-1 proteins show high levels of sequence similarity to their corresponding human and mouse counterparts. Sequence identities in the putative DNA-binding domains of chicken and human ICSBP and IRF-1 were 97% and 89%, respectively, whereas the C-terminal regions showed identities of 64% and 51%; sequence relationships with mouse ICSBP and IRF-1 are very similar. Chicken ICSBP was found to be expressed in several embryonic tissues, and both chicken IRF-1 and ICSBP were strongly induced in chicken fibroblasts by IFN treatment, supporting the involvement of these factors in IFN-regulated gene expression. The presence of proteins homologous to mammalian IRF family members, together with earlier observations on the occurrence of functionally homologous IFN-responsive elements in chicken and mammalian genes, highlights the conservation of transcriptional mechanisms in the IFN system, a finding that contrasts with the extensive sequence and functional divergence of the IFNs.

Recombinant chicken interferon from Escherichia coli and transfected COS cells is biologically active

We have expressed a cDNA for virus-induced chick interferon in Escherichia coli. The product, a 19-kDa protein lacking the signal peptide, was purified to homogeneity from the bacterial inclusion bodies. Proteins in the insoluble fraction of bacterial lysates were dissolved in guanidine hydrochloride and subjected to chromatography on Q-Sepharose and MonoS columns. Purified recombinant chick interferon has a specific antiviral activity of approximately 10(8) IU/mg and is a powerful inducer of the interferon-responsive promoter of the chicken Mx gene. Culture medium of transfected COS cells expressing full-length chick interferon cDNA contained up to 5 x 10(4) IU antiviral activity/ml that could be neutralized by antibodies to purified recombinant chick interferon. The antibodies precipitated proteins of 23-28 kDa from the supernatants of transfected COS cells. Treatment with endoglycosidase F reduced the size of the immunoprecipitated proteins to approximately 20 kDa, demonstrating that chick interferon is a glycoprotein.

Recombinant chicken interferon: a potent antiviral agent that lacks intrinsic macrophage activating factor activity

Crude preparations of chicken interferon (ChIFN) from various sources contain both antiviral and macrophage-activating factor (MAF) activity. Previous serological data indicated that unlike mammals, birds might express only a single type of IFN in response to viruses and mitogens that exhibits both activities. We have now expressed a complementary DNA for virus-induced ChIFN in transfected COS cells and in Escherichia coli. Purified recombinant ChIFN is a powerful antiviral agent and has high Mx promoter-inducing activity. However, as the sole agent, recombinant ChIFN lacks MAF activity: it does not induce the secretion of nitric oxide in primary monocyte-derived chicken macrophages. A neutralizing antiserum prepared against cloned ChIFN blocks most of the antiviral and Mx promoter-inducing activity present in preparations of natural ChIFN, but does not inhibit the MAF activity. These results demonstrate that chicken cells can be induced to secrete a novel cytokine which probably represents the avian homolog of mammalian IFN-gamma.

The interferon-induced Mx protein of chickens lacks antiviral activity

cDNA sequencing revealed that chick Mx protein consists of 705 amino acids. Its 84 N-terminal amino acids show no significant sequence homology to other Mx proteins. They are followed by 514 residues that include a tripartite GTP binding consensus motif. This region shows 50-70% sequence identity to mammalian and duck Mx proteins. Sequences near the C terminus, including a leucine zipper motif, are also conserved, whereas the intervening 19 amino acids lack sequence similarity. This unique sequence corresponds to a highly variable region in mammalian Mx proteins, suggesting that it serves as a spacer between functional domains. Chick and mouse cells transiently transfected with cDNA expression constructs synthesized chick Mx protein at a level that could easily be detected with specific antibodies. Chick Mx protein in such cells was mainly cytoplasmic and had a granular appearance. Permanently transfected cell lines expressing high levels of chick Mx protein could not be established, suggesting low metabolic stability of chick Mx protein or incompatibility with cell proliferation. The antiviral activity of chick Mx protein was tested at the single-cell level using immunofluorescence techniques. Transfected cells expressing chick Mx protein showed no enhanced resistance to influenza A virus, vesicular stomatitis virus, Thogoto virus, or Sendai virus. Thus, chick Mx joins the list of Mx proteins without recognized antiviral activity, supporting the concept that Mx proteins serve unrelated functions.

Inhibition of cytotoxicity of chicken granulocytes by serotonin and ketanserin

Serotonin (5-HT) has been observed to impair the cytotoxicity of human natural killer (NK) cells. A study has now been made of the effect of 5-HT on the cytotoxic activity of chicken granulocytes. 5-HT at concentrations of 10(-3) to 10(-6) M inhibited the cytotoxicity of chicken granulocytes when added at the onset of the short-term cytotoxicity assay. Ketanserin, a 5-HT2 receptor antagonist, did not reverse the inhibitory effect of 5-HT on chicken granulocyte cytotoxicity. Moreover, ketanserin at concentrations of 5 x 10(-4) to 5 x 10(-7) M inhibited the cytotoxicity mediated by chicken granulocytes. Pretreatment of the effector cells for 2 h with chick fibroblast interferon reduced the inhibition of chicken NK cytotoxicity induced by 5-HT and by ketanserin. These data indicate that, in birds, the neurotransmitter 5-HT serves as a link between the central nervous system and the immune system, and that interferon can modulate the inhibitory effect of 5-HT on the function of cytotoxic granulocytes.

Interferon induction of chicken MHC class I gene expression: phylogenetic conservation of the interferon-responsive element

The 5' upstream region of a chicken MHC class I gene BF-IV contains sequence motifs similar to the interferon consensus sequences (ICS) contained in promoters of many mammalian interferon-regulated genes. To study a possible functional role of this putative chicken ICS, an oligonucleotide spanning the upstream sequences of the BF-IV gene (-174/-194) was cloned singly or in multiple copies before the herpes TK promoter controlling the chloramphenicol acetyl transferase (CAT) gene (pBLCAT2). Transient expression studies performed with primary chicken fibroblasts (CEF) showed that the chicken ICS represses constitutive promoter activity. The chicken ICS, however, enhanced CAT activity up to 20-fold following treatment with chicken interferon (IFN). Deletion analysis of the BF-IV promoter also confirms that the upstream DNA sequences (-174/-194) contain a functional ICS recognized by chicken interferon. The murine ICS of the H2-Ld gene was also activated by chicken interferon when introduced into CEF. IFN activation of chicken ICS containing reporters was also observed in transformed chicken fibroblast lines. We show that the chicken ICS binds two specific nuclear factors present in chicken fibroblasts which are induced by interferon. These factors were also capable of recognizing the mouse ICS, suggesting the conservation of a relevant DNA-binding protein. Taken together, these data indicate that the chicken ICS motif contained in a sequence from -174 to -194 of the BF-IV gene acts as a strong interferon-response element, which has been functionally conserved during about 270 million years of separate evolution of mammals and birds.

Transforming growth factor-beta 1 rapidly induces Hsp70 and Hsp90 molecular chaperones in cultured chicken embryo cells

In this report we show that: (1) molecular chaperones in the heat shock protein (hsp) family are a new class of cellular proteins induced by Transforming Growth Factor-beta 1 (TGF beta), a cytokine present in serum, (2) rapid induction of Hsc70 precedes a general increase in protein synthesis and may be a preparatory event, (3) TGF beta is a potent regulator of overall protein synthesis in chicken embryo cells (CEC), and (4) isoforms of Hsp90 with different biochemical properties exist, raising the possibility that they may have different functions. TGF beta can substitute for serum in stimulating synthesis of members of the Hsp90 and Hsp70 families of stress proteins, whereas other cytokines, including PDGF, FGF, and EGF, were not effective nor did they enhance the stimulatory effect of TGF beta on the hsp's. Analysis of the induction of hsp's using one- and two-dimensional polyacrylamide gel electrophoresis indicated that members of the Hsp70 family of molecular chaperones were induced rapidly by TGF beta, reaching maximum rates of accumulation by 5 hours of treatment. Total protein synthesis increased more slowly, undergoing an approximately twofold increase in 24 hours. Using a modified protocol for two-dimensional gel electrophoresis, the Hsp90 protein family was separated into four isoelectric forms, two of which were phosphorylated (Hsp90-2 and -4). These phosphorylated isoforms turned over faster than the unphosphorylated forms of Hsp90. All four isoforms were heat inducible, but only Hsp90-2 and -3 were induced rapidly by TGF beta, again within 5 hours of treatment. The effects of serum on these protein families were similar to those of TGF beta, suggesting that this cytokine may be the serum component primarily responsible for up-regulating members of the Hsp90 and Hsp70 families. We hypothesize that cells rapidly increase their chaperoning capacity for newly synthesized polypeptides in preparation for an increase in the rate of synthesis of proteins up-regulated by TGF beta.

Basal expression of the histone H5 gene is controlled by positive and negative cis-acting sequences

Sequences from -3500 to +1365 of the chicken histone H5 gene have been analyzed for the presence of cis-acting elements in H5 expressing (transformed CFU-E) and non-expressing cells (fibroblasts). The region from -3500 to -115 had little effect on transcription. Proximal upstream sequences contain a negative element (UNE, -115 to -95), capable to also repress the activity of the heterologous HSV tk promoter, and two positive elements, a consensus GC-box (-83 to -74) and a proximal element (UPE, -54 to -38). The sequence of the UPE is highly related to the histone H4 subtype-specific element and it has been conserved in the duck H5 and the human and mouse H1(0) genes at equivalent positions. Although the effect of the UNE, GC-box and UPE was not tissue-specific, sequences from -38 to +77 appear to confer a degree of tissue specificity to the promoter. An activating erythroid-specific element (DE) was found downstream of the H5 gene (+1042 to +1185). The activity of the DE was modest but independent of position and orientation and required the presence of the promoter proximal elements. The DE harbors the sequence AGATAA that is recognized by a protein factor, presumably the same that binds to other erythrocyte-specific enhancers. The low activity of DE in the CFU-E may be related to the low concentration of the AGATAA-binding factor in the differentiation-blocked cells.

A continuous line of chicken embryo cells derived from a chondrocyte culture infected with RSV

A continuous line of chicken embryo cells was derived from a culture of chondrocytes infected with Rous sarcoma virus (RSV). These cells, designated as NA101, have reduced serum requirements and are able to grow in a semisolid medium. NA101 cells show the same phenotype as freshly RSV infected chondrocyte cultures, i.e. synthesis of fibronectin and type I collagen, elongated bipolar shape and absence of tumorigenicity following grafting onto the chorioallantoic membrane of embryonated duck eggs; thus they appear to be distinct from transformed fibroblasts. Neither NA101 cells nor freshly infected chondrocyte cultures synthesize type II or type X collagen, which are the differentiation markers of normal chicken chondrocytes in culture.

The cytoplasmic domain of the cell adhesion molecule uvomorulin associates with three independent proteins structurally related in different species

Uvomorulin belongs to the group of Ca2+-dependent cell adhesion molecules, which are integral membrane proteins with several structural features in common. In particular, the cytoplasmic part of these proteins is highly conserved in different species, suggesting a common biological function. To test this assumption we transfected a uvomorulin full-length cDNA into uvomorulin-negative mouse NIH 3T3 and L cells. Immunoprecipitations with anti-uvomorulin antibodies detected, in addition to uvomorulin, three independent proteins of 102, 88 and 80 kd which are of host origin and which form complexes with uvomorulin. Using cDNA constructs coding for uvomorulin with cytoplasmic or extracellular deletions it is shown that the 102, 88 and 80 kd proteins complex with the cytoplasmic domain of uvomorulin. Peptide pattern analysis revealed that these three proteins are identical in different mouse cells. When uvomorulin cDNA was introduced into cell lines from other species, such as human HeLa and avian fibroblasts, the expressed uvomorulin was also associated with endogenous 102, 88 and 80 kd proteins and, moreover, each of these proteins showed structural similarities to the respective mouse molecule. A panel of antibodies specific for known cytoplasmic proteins of mol. wts similar to those of the three proteins did not react with any of the described components. This suggests that the 102, 88 and 80 kd proteins constitute a new group of proteins for which we propose the nomenclature of catenin alpha, beta and gamma respectively. The characterization of these proteins provides a first molecular basis for a possible cytoplasmic anchorage of uvomorulin to the cytoskeleton.

Development and characterization of continuous avian cell lines depleted of mitochondrial DNA

Populations of quail and chicken cells were treated with ethidium bromide, an inhibitor of mitochondrial DNA replication. After long-term exposure to the drug, the cell populations were transferred to ethidium bromide (EtdBr)-free medium, and cloned. Clones HCF7 (quail) and DUS-3 (chicken) were propagated for more than a year, and then characterized. Analysis of total cellular DNA extracted from these cells revealed no characteristic mitochondrial DNA molecule by Southern blot hybridization of HindIII- or AvaI-digested total cellular DNA probed with cloned mitochondrial DNA fragments. Reconstruction experiments, where a small number of parental cells was mixed with HCF7 cells and DUS-3 cells before extraction of total cellular DNA, further strengthen the notion that the drug-treated cells are devoid of mitochondrial DNA molecules. The cell populations were found to proliferate at a moderately reduced growth rate as compared to their respective parents, to be auxotrophic for uridine, and to be stably resistant to the growth inhibitory effect of EtdBr and chloramphenicol. At the ultrastructural level, mitochondria were considerably enlarged and there was a severe reduction in the number of cristae within the organelles and loss of cristae orientation. Morphometric analysis revealed a fourfold increase of the mitochondrial profile area along with a twofold decrease of the numerical mitochondrial profiles. Analysis of biochemical parameters indicated that the cells grew with mitochondria devoid of a functional respiratory chain. The activity of the mitochondrial enzyme dihydroorotate dehydrogenase was decreased by 95% and presumably accounted for uridine auxotrophy.

Development and characterization of mutant chicken cell lines for somatic cell genetics studies

A series of stable mutants bearing nuclear genetic markers were developed from the established chicken cell line DU24. The mutants were obtained after mutagenesis of DU24 cells with ethyl methanesulfonate (EMS) or arose spontaneously when plated in the appropriate selective medium. Clones resistant to 5-bromodeoxyuridine (BrdU) were obtained following a two-step selection procedure and analyzed. The BrdUr cells were found to be deficient in thymidine kinase activity and were HAT sensitive. Molecular characterization of these mutants revealed no deletions or other rearrangements, but methylation of some cytosine residues was decreased in the mutants. A similar restriction profile was seen in a series of mutants made resistant to BrdU after cultivation of DU24 cells in increasing concentrations of the drug over a period of six months. Selection of EMS-treated BrdUr cells in 10 microM ouabain gave rise to a clone resistant to both drugs and which was still HAT sensitive. Clones resistant to 6-thioguanine were also isolated, but showed wild-type hypoxanthine phosphoribosyltransferase activity and were HAT resistant. A number of the cell lines isolated were found to be suitable for fusion experiments with both chicken cells and cells from other vertebrate species.

Lysozyme gene activity in chicken macrophages is controlled by positive and negative regulatory elements

The chicken lysozyme gene is constitutively active in macrophages and under the control of steroid hormones in the oviduct. To investigate which DNA elements are involved in the control of its expression in macrophages we performed transient DNA transfer experiments with two different types of plasmids: 5'-deletion mutants of the upstream region of the chicken lysozyme gene and different fragments from this area in front of the thymidine kinase promoter (herpes simplex virus), each placed in front of the CAT (chloramphenicol acetyl transferase) coding sequence. Two enhancers (E-2.7 kb and E-0.2 kb) were characterized. They are active in macrophages, but not in chicken fibroblasts. Furthermore a negative element (N-2.4 kb) was identified, which is active in fibroblasts and promyelocytes, but not in mature macrophages. The combined action of all three elements contributes to the observed lysozyme gene activities: no activity in fibroblasts, moderate activity in promyelocytes and high activity in mature macrophages.

Granulocyte-specific monoclonal antibody inhibiting cytotoxicity reactions in the chicken

Monoclonal antibody (MAb) 1C3, specific for chicken granulocytes, is described for the first time. Treatment of peripheral blood leukocytes with this MAb markedly decreased natural cytotoxicity reaction against the target cell line. The antibody-dependent cellular cytotoxicity (ADCC) activity of purified granulocytes was also severely affected by treatment with MAb 1C3. These results suggest that 1C3 detects a functional surface antigen on chicken granulocytes and support the hypothesis that granulocytes are the main effector cells in natural cytotoxicity in the chicken.

Cellular senescence revisited: a review

The field of cellular senescence (cytogerontology) is reviewed. The historical precedence for investigation in this field is summarized, and placed in the context of more recent studies of the regulation of cellular proliferation and differentiation. The now-classical embryonic lung fibroblast model is compared to models utilizing other cell types as well as cells from donors of different ages and phenotypes. Modulation of cellular senescence by growth factors, hormones, and genetic manipulation is contrasted, but newer studies in oncogene involvement are omitted. A current consensus would include the view that the life span of normal diploid cells in culture is limited, is under genetic control, and is capable of being modified. Finally, embryonic cells aging in vitro share certain characteristics with early passage cells derived from donors of increasing age.

The role of interferon in the adenovirus-induced augmentation of granulocyte-mediated cytotoxicity in chicken

The effects of human adenoviruses on the granulocyte-mediated natural cytotoxicity of chicken leukocytes were investigated. A significant, but transient augmentation of granulocyte cytotoxicity was observed 24 h after virus injection, followed by a relatively long period of its suppression. A good correlation was found between the augmented cytotoxicity and interferon induction. The interferon-inducing capacity of adenovirus type 6 and type 12 in vitro similarly ran parallel with their ability to stimulate granulocyte-mediated cytotoxicity. An adenovirus-induced elevation of cytotoxicity was not observed when IFN production was inhibited by pretreatment of the leukocytes with monoclonal antibody specific for bursal cells and monocytes. In addition, anti-IFN antibody abrogated the stimulation of cytotoxicity as well. During the in vitro experiments in which granulocyte-specific monoclonal antibody was applied, evidence was found that the effector cell activity is associated with the granulocytes. These results suggest that both the in vitro and the in vivo adenovirus-induced augmentation of granulocyte-mediated cytotoxicity is due to the IFN-inducing capacity of the virus. In chickens, the rapid augmentation of the granulocyte cytotoxicity may be important in the acute stage of infection, increasing the resistance to the virus in question and also to bacterial infections.

An established avian fibroblast cell line without mitochondrial DNA

An established avian fibroblast cell line (LSCC-H32) has been found to be inherently resistant to the growth-inhibitory effect of ethidium bromide, when supplied with exogenous uridine. After long-term exposure to ethidium bromide (90 days), the cell population has been transferred to drug-free medium for 60 days, and then seeded at low cell density. Three clones have been isolated and propagated in drug-free medium for 5, 6, and more than 12 months, respectively. It was found that none of these cell lines had detectable cytochrome c oxidase activity and that they were virtually devoid of cytochromes aa3 and b. Mitochondrial DNA was quantitated by DNA-DNA reassociation kinetics with a probe of chicken liver mitochondrial DNA. A mean number of 300 copies of mitochondrial DNA per cell was found in LSCC-H32 cells. Analysis of DNA extracted from cell populations exposed to ethidium bromide for 90 days and then transferred to drug-free medium for long periods of time revealed no mitochondrial DNA molecules by reassociation kinetics or by Southern blot hybridization of HindIII-or AvaI-digested total cellular DNA.

Are granulocytes the main effector cells of natural cytotoxicity in chickens?

Purified peripheral blood granulocytes from chicken were tested for cytotoxic activity against two types of virus-transformed chicken cell line, LSCC-H32 and LSCC-RP9. Strong cytotoxicity could be demonstrated, as measured in a 4-hr 51Cr-release assay, especially against the fibroblastoid LSCC-H32 cells. The degree of cytotoxicity was dependent on the E:T ratio. Normal CEF cells were completely resistant to the cytotoxicity. No cytotoxicity of human granulocytes could be observed against a variety of adherent and non-adherent target cells, as measured by the same microcytotoxicity technique. The priority of granulocytes in the natural cytotoxicity in the avian system is, therefore, suggested.

Use of chicken cell line LSCC-H32 for titration of animal viruses and exogenous chicken interferon

The chicken embryo cell line LSCC-H32 was tested for the propagation and titration of several animal viruses of the families Toga-, Reo-, Rhabdo-, Herpeto-, Orthomyxo-, Paramyxo-, and Poxviridae and compared with secondary chicken embryo cells. The LSCC-H32 cells were demonstrated to be as susceptible for most of the tested viruses as were secondary chicken embryo cells. Both produced comparably sized virus plaques. The titers of Sindbis and Semliki Forest viruses in LSCC-H32 cells were 5- to 40-fold higher than in secondary chicken embryo cells or BHK-21 cells, respectively. Furthermore, exogenous chicken standard interferon was titrated in the LSCC-H32 cells, and a 50% plaque titer reduction of the challenging vesicular stomatitis virus was achieved by 0.12 IU of a standard chicken interferon preparation. Endogenous chicken interferon could not be induced by treatment of the cells with polyinosinic acid-polycytidylic acid. Due to its high plating efficiency and metabolic activities, the LSCC-H32 cell line provides a useful cell system for the titration and large-scale production of the tested animal viruses and for the titration of exogenous chicken interferon.

Isolation of a line of immortal chicken embryo fibroblasts after transfection with the nuclei of Rous sarcoma virus-transformed Chinese hamster cells

Secondary cultures of chicken embryo fibroblasts were transfected with purified nuclei from lysed cells of a clonal line of temperature-sensitive Rous sarcoma virus (tsRSV)-transformed Chinese hamster fibroblasts. After propagation for 3 months an established cell line designated ChR32 was obtained in one chicken cell culture. The cells of this line have been propagated so far for 18 months, whereas normal chicken embryo fibroblasts died after 2 months. The established cells were heteroploid with a diploid modal number of macrochromosomes and two Z chromosomes. No Chinese hamster chromosomes could be identified. Southern blot analysis of DNA from the uncloned ChR32 cells and the clones provided evidence that these established cells were, in fact, clonal in origin and contained full-length RSV proviruses and no defective proviruses. Furthermore, they contained, at the 3' end proviral-cellular junction, Bg/II, HpaI, KpnI, SacI, and XbaI fragments of the same size as the Chinese hamster donor cells, suggesting that the cellular sequence adjacent to the provirus is of Chinese hamster origin. The cells after establishment were able to grow continuously at 37 degrees or 41 degrees C and produce a large amount of ts sarcoma virus particles. A corollary finding was that these virus particles were non-leaky for the transforming function at the non-permissive temperature.