Adenovirus inclusions in sheep liver

Comparative analysis of ovine adenovirus 287 and human adenovirus 2 and 5 based on their codon usage

Ovine adenovirus 287 (OAdV287) emerges as one of the most promising gene vectors resulting from its unique biological characteristics. To obtain a more detailed knowledge about the codon usage of OAdV287, a comparative study based on the codon usage of OAdV287 and the prototypes of human adenovirus serotypes 2 and 5 (HAdV2/5) was carried out. Some commonly used indices measuring the codon usage patterns, including effective number of codons, relative synonymous codon usage, and statistical methods, were adopted. Overall, OAdV287 had a more biased and conservative codon usage pattern than that of HAdV2/5. Both mutation pressure and natural selection played important roles in shaping the codon usage patterns of these three adenoviruses. All the preference codons of OAdV287 had A/U ends and were totally different from those of sheep and humans; however, the preference codons of HAdV2/5 mostly had G/C ends and were mostly coincident with those of sheep and humans. The codon usage analysis in this study supplies some clues for further comprehending the unique biological characteristics of OAdV287 as gene vectors.

An ovine adenovirus vector lacks transforming ability in cells that are transformed by AD5 E1A/B sequences

Adenoviruses of the Mastadenovirus and Aviadenovirus genera are able to transform certain cell types and induce tumor formation in susceptible animals. For the mastadenoviruses the E1A/B sequences are largely responsible for these properties but E4 sequences may also be involved. The transforming sequences of the aviadenoviruses, which lack E1A/B and E4 homologues, have not yet been fully identified. The recent proposal for a third genus of adenoviruses, which apparently lack an E1A homologue and have weak E1B homology, prompted an examination of the transforming properties of ovine adenovirus OAV287 (OAV), the prototype member of the new group. When OAV and human adenovirus type 5 (Ad5) were used to infect primary rat embryo cells, transformed foci developed in Ad5- but not in OAV-infected cultures. Similarly, after plasmid transfection, baby rat kidney cells were transformed by Ad5 E1A/B but not by OAV sequences. When CSL503 cells, an ovine cell line that is permissive for OAV, were transfected with Ad5 E1A/B sequences, transformed foci again appeared. However, plasmids or fragments containing complete or partial OAV genome sequences did not detectably transform CSL503 cells under the same conditions. When Ad5 E1A/B sequences were incorporated into the complete OAV genome and transfected, transformed clones were again obtained, showing that the gene dosage and transfection conditions were not limiting for transformation. The provision of Ad5 E1A and OAV sequences in combination marginally increased the number of morphologically altered foci in baby rat kidney cells but failed to induce multilayered focus formation. The data suggest that OAV lacks transforming functions in the cell types examined. Additional information suggesting that OAV may have a fundamentally distinct strategy for replication compared with other Ads is discussed.

DNA sequencing and phylogenetic analysis of the protease gene of ovine adenovirus 3 suggest that adenoviruses of sheep belong to two different genera

Until now, the only published ovine adenovirus DNA sequence was the complete genome of ovine adenovirus isolate 287 (OAV287) which, compared to other mammalian adenoviruses, possesses strikingly unique genomic organisation and should properly be classified into a new adenovirus genus. The protease gene sequence of ovine adenovirus type 3 (OAdV-3) was determined and analysed. The results of phylogenetic analysis of the 205 residue long protein demonstrated that OAdV-3 belongs to the genus Mastadenovirus, and is surprisingly closely related to bovine adenovirus type 2. In spite of the common host origin, the evolutionary distance between OAdV-3 and OAV287 proved to be great suggesting that sheep, similarly to cattle and fowl, might be infected by distantly related adenoviruses belonging to different genera.

Identification of transcripts and promoter regions of ovine adenovirus OAV287

The ovine adenovirus isolated OAV287 represents a new group of adenoviruses that are distinct from the Mast- and Aviadenoviruses by several criteria, including genome arrangement. The OAV major late promoter and some late transcripts were previously mapped. To better define the probable coding sequences and to identify the approximate location of early promoters a partial transcription map of the genome was elucidated using a PCR-based approach. This was possible because the complete nucleotide sequence of the genome was known. The strategy permitted the identification of transcription start sites and RNA splice junctions and allowed the approximate location of promoters in the lefthand end, IVa2, E2, P32K, and E4 regions to be deduced. The data showed that lefthand end and E4 regions are controlled by three and two temporally distinct promoters, respectively. The E2 region is controlled by a single promoter, in contrast to Mastadenoviruses, where E2 expression is controlled by the E2A and E2B promoters. The p32kDa structural protein at the lefthand end and the IVa2 protein are also expressed from their own promoters. These data contribute to the first overview of transcription from a non-Mastadenovirus genome.

Gene expression by atypical recombinant ovine adenovirus vectors during abortive infection of human and animal cells in vitro

An bovine adenovirus, which is phylogenetically distinct from the Mastadeno- and Aviadenoviruses, was used to construct recombinants in which reporter genes were expressed from the OAV major late, or human cytomegalovirus promoters. It was demonstrated by transgene expression that OAV could infect bovine nasal turbinate and rabbit kidney cells as well as a range of human cell types, including lung and foreskin fibroblasts as well as liver, prostate, breast, colon, and retinal lines. Some human lines, e.g., 293 and LNCaP were not detectably infected. Infection occurred even though OAV has a fiber protein with a unique cell binding domain and a penton protein that lacks the integrin-binding Arg-Gly-Asp motif which facilitates entry by human adenoviruses. Most cell lines showed little or no ill effect for several days after infection but a prominent cytopathic effect appeared in fibroblasts after 3-4 days. However, no viral DNA synthesis was detected and replication was abortive. Viral promoter activity during infection of nonpermissive cell types was assayed by RT-PCR. Early promoter activity was detectable in some, but not all cell types. In a liver and a colon carcinoma cell line, none of the promoters examined was significantly active, even when a higher multiplicity of infection was used. Major late promoter activity was not detectable in any cell type. The lack of DNA replication and MLP function suggests that a critical transition from early to late gene expression does not occur during abortive infection by OAV.

Characterisation of Australian ovine adenovirus isolates

We have characterised two groups of adenoviruses isolated from sheep in Australia. Restriction endonuclease maps for enzymes BamHI, ClaI, SalI, SmaI and SphI have been determined for the genome of ovine adenoviruses related to bovine adenovirus serotype 7 (BAV 7) from sheep in Western Australia. Although previously serotyped as BAV 7 these isolates are different from bovine isolates of BAV 7 based on comparison with published restriction endonuclease profiles and maps of BAV 7 cattle isolates. Additional adenovirus isolates obtained from Victorian sheep have been serotyped as ovine adenovirus type 5 (OAV 5). On the basis of restriction endonuclease analysis these viruses are different from the sheep BAV 7 isolates. Following infection of sheep with ovine BAV 7 and OAV 5 isolates, virus was recovered from nasal and rectal swabs for several days. Antibodies detected by ELISA and serum neutralisation tests (SN) developed by 15 days after infection. Virus also spread from the infected sheep to an incontact control and one of ten sheep purchased for infection studies had SN antibodies to BAV 7 suggesting that BAV 7-like viruses naturally infect sheep in Victoria and Western Australia. With further development, these ovine adenoviruses may be suitable as vectors for the delivery of vaccine antigens to sheep and cattle.

Pulmonary lesions in lambs experimentally infected with ovine adenovirus 5 strain RTS-42

Twelve lambs were inoculated transtracheally and intranasally with Mastadenovirus ovi 5 strain RTS-42 and killed sequentially. Pulmonary lesions were studied by light and electron microscopy. Four lambs served as sham inoculated controls. Pulmonary lesions consisted of multifocal areas of bronchiolitis and alveolitis associated with necrosis and sloughing of isolated type I and type II alveolar epithelial cells and nonciliated bronchiolar epithelial cells. This was followed rapidly by hyperplasia of the remaining epithelium and repair of the damage. A cellular infiltrate of neutrophils and macrophages began at 2 days after inoculation, peaked at 4 days after inoculation, gradually diminished until minimal at 12 days after inoculation, and was resolved at 21 days after inoculation. Surfactant was abundant and, along with debris, was removed from the alveoli by macrophages. Clinical disease was not seen, but lesions were believed to be sufficient to allow bacteria to colonize the lungs and cause severe disease.