Unraveling the genome structure of cyanobacterial podovirus A-4L with long direct terminal repeats.

The freshwater cyanobacterial virus (cyanophage) A-4L, a podovirus, can infect the model cyanobacterium Anabaena sp. strain PCC 7120 resulting in a high burst size and forming concentric plaques on its lawns. The complete genome sequence of A-4L was determined by the combination of high-throughput sequencing, terminal transferase-mediated polymerase chain reaction and restriction mapping. It contains 41,750 bp with 810 bp direct terminal repeats and 38 potential open reading frames. As compared with other cyanobacterial podoviruses in diverse ecosystems, the A-4L has the longest terminal repeat and shares similar genome organizations with freshwater members. Furthermore, phylogenetic analysis based on concatenated sequences of eight core proteins indicated that freshwater cyanobacterial podoviruses were clustered together and distinct from marine counterparts, suggesting a clear divergence in the cyanobacterial podovirus lineage between freshwater and marine ecosystems. Our findings uncover the unique genome structure of A-4L which contains long direct terminal repeats, and create the first model system to address knowledge gaps in understanding cyanobacterial virus-host interactions at the molecular level.

Thymus cDNA library survey uncovers novel features of immune molecules in Chinese giant salamander Andrias davidianus.

A ranavirus-induced thymus cDNA library was constructed from Chinese giant salamander, the largest extant amphibian species. Among the 137 putative immune-related genes derived from this library, these molecules received particular focus: immunoglobulin heavy chains (IgM, IgD, and IgY), IFN-inducible protein 6 (IFI6), and T cell receptor beta chain (TCRß). Several unusual features were uncovered: IgD displays a structure pattern distinct from those described for other amphibians by having only four constant domains plus a hinge region. A unique IgY form (IgY(ΔFc)), previously undescribed in amphibians, is present in serum. Alternative splicing is observed to generate IgH diversification. IFI6 is newly-identified in amphibians, which occurs in two forms divergent in subcelluar distribution and antiviral activity. TCRß immunoscope profile follows the typical vertebrate pattern, implying a polyclonal T cell repertoire. Collectively, the pioneering survey of ranavirus-induced thymus cDNA library from Chinese giant salamander reveals immune components and characteristics in this primitive amphibian.

Extensive diversification of MHC in Chinese giant salamanders Andrias davidianus (Anda-MHC) reveals novel splice variants.

A series of MHC alleles (including 26 class IA, 27 class IIA, and 17 class IIB) were identified from Chinese giant salamander Andrias davidianus (Anda-MHC). These genes are similar to classical MHC molecules in terms of characteristic domains, functional residues, deduced tertiary structures and genetic diversity. The majority of variation between alleles is found in the putative peptide-binding region (PBR), which is driven by positive Darwinian selection. The coexistence of two isoforms in MHC IA, IIA, and IIB alleles are shown: one full-length transcript and one novel splice variant. Despite lake of the external domains, these variants exhibit similar subcellular localization with the full-length transcripts. Moreover, the expression of MHC isoforms are up-regulated upon in vivo and in vitro stimulation with Andrias davidianus ranavirus (ADRV), suggesting their potential roles in the immune response. The results provide insights into understanding MHC variation and function in this ancient and endangered urodele amphibian.