Analysis of channel catfish virus direct repeat region gene expression.

摘要

Channel catfish virus (CCV) is an unclassified herpesvirus. CCV causes massive mortalities in cultured channel catfish fry and fingerling populations each summer. CCV DNA may be detected in several tissues, including the leukocytes, of latently infected fish. CCV virion size and structure, and genomic organization into unique and repeated regions resemble those of mammalian herpesviruses. The CCV protein production cascade indicates that CCV transcription is temporally regulated into immediate-early (IE), early and late stages, similar to that of mammalian herpesviruses. IE gene products are often involved in viral transcriptional regulation. Early gene products are generally involved in viral genome replication. Late gene products are usually structural. Herpesvirus repeat regions often contain IE genes and other pathogenically important genes. The goals of this work are to compare CCV gene expression from the direct repeat region to that of other herpesviruses, and to provide a foundation for molecular studies using CCV as a natural model of herpesvirus infection. Evaluation of the putative transcriptional cascade of CCV in channel catfish ovary (CCO) cells, using metabolic inhibitors to distinguish transcriptional stages, confirmed that CCV transcription is temporally regulated. The CCV direct repeat regions expressed IE transcripts (from genes 1 and 3), early transcripts (from genes 2–9, and 11–14), and late transcripts (from genes 4, 7 and 10–13). Evaluation of the transcriptional regulatory activities of the products of IE genes 1 and 3 and early gene 9 (a putative zinc-binding protein) indicated no such activity. For in vivo studies, an experimental infection model mimicking natural CCV infection of channel catfish was developed as a source of acutely and latently infected fish. Expression of genes from each of the transcriptional stages (IE 1, IE 3, early 5 and late 10) was detected in infected CCO cells and acutely infected fish brain, kidney, liver and blood, but not in latently infected fish blood. This study has significantly advanced our understanding of CCV molecular biology and has developed a model of natural herpesvirus infection that may lead to further discoveries about herpesvirus molecular processes during acute and latent infection.