Transient expression of a viral histone H4 inhibits expression of cellular and humoral immune-associated genes in Tribolium castaneum.
A viral histone H4 is encoded in a polydnavirus called Cotesia plutellae bracovirus (CpBV), which is symbiotic to an endoparasitoid wasp, C. plutellae. Compared to general histone H4s, the viral H4 possesses an extra N-terminal tail containing 38 amino acid residues, which has been presumed to control host gene expression in an epigenetic mode. To analyze the epigenetic control activity of CpBV-H4 on expression of immune-associated genes, it was transiently expressed in larvae of Tribolium castaneum that had been annotated in the immune genes from a full genome sequence. Subsequent alteration of gene expression pattern was compared with that of its mutant form deleting N-terminal tail (truncated CpBV-H4). In response to bacterial challenge, T. castaneum induces expression of 13 antimicrobial peptide (AMP) genes. When CpBV-H4 was expressed, the larvae failed to express 12 inducible AMP genes. By contrast, when truncated CpBV-H4 was transiently expressed, all AMP genes were expressed. Hemocyte nodule formation was significantly impaired by expression of CpBV-H4, in which expressions of tyrosine hydroxylase and dihydroxyphenylalanine decarboxylase were suppressed. However, expression of truncated CpBV-H4 did not give any significant adverse effect on the cellular immunity. The immunosuppression of CpBV-H4 was further supported by its activity of enhancing bacterial pathogenicity of an entomopathogenic bacterium, Xenorhabdus nematophila, against larvae transiently expressing CpBV-H4. These results suggest that CpBV-H4 suppresses both humoral and cellular immune responses of T. castaneum by altering a normal epigenetic control of immune-associated gene expression.
Department of Bioresource Sciences, Andong National University, Andong 760-749, Republic of Korea.
Rahul
R
Hepat
Yonggyun
Y
Kim
D000818:Animals; D044127:Epigenesis, Genetic; D006657:Histones / Q000235:genetics*; D007111:Immunity, Cellular / Q000235:genetics*; D056724:Immunity, Humoral / Q000235:genetics*; D018071:Polydnaviridae / Q000235:genetics*; D014231:Tribolium / Q000235:genetics / Q000276:immunology* / Q000821:virology*; D014764:Viral Proteins / Q000235:genetics*
D006657:Histones; D014764:Viral Proteins