The ORF RTL1 transcript of fowl adenovirus type-8 is spliced and truncated at late stages of the virus replication cycle

Antibody response and virus tissue distribution in chickens inoculated with wild-type and recombinant fowl adenoviruses

We demonstrated that the long tandemly repeated region (TR-2) is dispensable for in vitro replication of fowl adenovirus 9 (FAdV-9). The TR-2-deleted recombinant FAdV-9 expressing the enhanced green fluorescence protein was further characterized for in vivo effects. Groups of chickens were exposed to recombinant or wild-type FAdV-9 by intramuscular injection, through the feed or drinking water and one group served as a negative control. The antibody (Ab) response, evaluated by ELISA and a plaque reduction test depended on the virus, dosage and the route of inoculation. Although the highest levels of anti-viral Ab were detected in chickens inoculated intramuscularly (i.m.) with wild-type FAdV-9, the deletion of TR-2 did not have a significant effect on the immune response. The tissue distribution of the virus was examined by the polymerase chain reaction (PCR) and was similar for both wild-type and recombinant viruses. Based on these results the TR-2 was dispensable for viral replication in vivo and did not influence virus distribution, and the recombinant FAdV-9 induced the same immune response as the wild-type virus.

Unique features of fowl adenovirus 9 gene transcription

We examined the transcriptional organization of fowl adenovirus 9 (FAdV-9) and analyzed temporal transcription profiles of its early and late mRNAs. At least six early and six late transcriptional regions were identified for FAdV-9. Extensive splicing was observed in all FAdV-9 early transcripts examined. Sequence analysis of the cDNAs representing the early proteins identified untranslated leader sequences, precise locations of splice donor and acceptor sites, as well as polyadenylation signals and polyadenylation sites. A unique characteristic, compared to other adenoviruses, was the detection by RT-PCR of multiple transcripts specific for each of five late genes (protein III, pVII, pX, 100K, and fiber), suggesting that FAdV-9 late transcripts undergo more extensive splicing than reported for other adenoviruses.

The long repeat region is dispensable for fowl adenovirus replication in vitro

Two regions containing tandemly repeated sequences are present in the fowl adenovirus 9 (FAdV-9) genome. The longer repeat region (TR-2) is composed of 13 contiguous 135-bp-long direct repeats, the function of which is unknown. An infectious FAdV-9 genomic clone, constructed by homologous recombination in Escherichia coli, was used for engineering of recombinant viruses. The enhanced green fluorescence protein (EGFP) coding sequence was cloned in both rightward and leftward orientations so as to replace TR-2. Replication-competent recombinant FAdVs were recovered, demonstrating that TR-2 was dispensable for FAdV-9 propagation in vitro. The expression of EGFP in infected cells was demonstrated by fluorescence microscopy, immunoprecipitation, and RT-PCR.