Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2002
Publication Date: May 25, 2003
Citation: Cheung, A.K. 2003. Comparative analysis of the transcriptional patterns of pathogenic and nonpathogenic porcine circoviruses. Virology. 310(1):41-49. Interpretive Summary: Two genotypes of porcine circovirus (PCV) have been identified. PCV type 1 (PCV1) is widespread in swine, but no known animal disease has been associated with PCV1. PCV type 2 (PCV2) is the causative agent of a new disease named postweaning multisystemic wasting syndrome (PMWS); and PMWS has been reported worldwide. The genome sequences of a number of PCV1 and PCV2 isolates have been determined. The overall DNA sequence homology within the PCV1 or PCV2 isolates is greater than 90%, while the homology between PCV1 and PCV2 isolates is 68-76%. However, the genetic basis for PCV2 pathogenicity cannot be discerned from the genomic sequences. Therefore, it is important to examine the genes expressed by PCV1 and PCV2. We identified several new PCV2 genetic elements that are different from the nonpathogenic PCV type 1. This work provides a general framework to elucidate the genetic basis for PCV2 pathogenicity and a method to screen for attenuated viruses for vaccine development.
Technical Abstract: The RNAs of porcine circovirus type 1 (PCV1) synthesized in PK15 cells were characterized. A total of 12 RNAs were detected. They include the viral capsid protein RNA (CR), a cluster of 8 Rep-associated RNAs (designated Rep, Rep', Rep3a, Rep3b, Rep3c-1, Rep3c-2, Rep3c-3 and Rep3c-4), and 3 NS-associated RNAs (designated NS462, NS642 and NS0). Members of the Rep-associated RNA cluster all share common 5' and 3' nucleotide sequences and they share common 3' nucleotide sequence with the NS-associated RNAs. Rep, capable of coding for the full-length replication associated protein, appears to be the primary transcript that gives rise to the other 7 Rep-associated RNAs by alternate splicing. NS462, NS642 and NS0 appear to have been transcribed from 3 different promoters present inside ORF1, independent from the Rep promoter. Based on sequence alignment analysis, both the non-pathogenic PCV1 and the pathogenic porcine circovirus type 2 (PCV2) (with 9 RNAs: Rep, Rep' Rep3a, Rep3b, Rep3c, NS515, NS672 and NS0) utilize comparable genetic elements similarly located along the genome for viral gene expression. The Rep, Rep' Rep3a, Rep3b and NS0 of PCV1 and PCV2 are considered equivalent entities in their respective systems. However, quantitative and qualitative differences (splice junction variation) were observed among the Rep3c and NS-associated RNAs. This work provides a general framework and genetic basis to investigate the biologic properties (and differences) of PCV1 and PCV2.