Coevolution of hytrosaviruses and host immune responses

Abstract

BackgroundHytrosaviruses (SGHVs; Hytrosaviridae family) are double-stranded DNA (dsDNA) viruses that cause salivary gland hypertrophy (SGH) syndrome in flies. Two structurally and functionally distinct SGHVs are recognized; Glossina pallidipes SGHV (GpSGHV) and Musca domestica SGHV (MdSGHV), that infect the hematophagous tsetse fly and the filth-feeding housefly, respectively. Genome sizes and gene contents of GpSGHV (~ 190 kb; 160–174 genes) and MdSGHV (~ 124 kb; 108 genes) may reflect an evolution with the SGHV-hosts resulting in differences in pathobiology. Whereas GpSGHV can switch from asymptomatic to symptomatic infections in response to certain unknown cues, MdSGHV solely infects symptomatically. Overt SGH characterizes the symptomatic infections of SGHVs, but whereas MdSGHV induces both nuclear and cellular hypertrophy (enlarged non-replicative cells), GpSGHV induces cellular hyperplasia (enlarged replicative cells). Compared to GpSGHV’s specificity to Glossina species, MdSGHV infects other sympatric muscids. The MdSGHV-induced total shutdown of oogenesis inhibits its vertical transmission, while the GpSGHV’s asymptomatic and symptomatic infections promote vertical and horizontal transmission, respectively. This paper reviews the coevolution of the SGHVs and their hosts (housefly and tsetse fly) based on phylogenetic relatedness of immune gene orthologs/paralogs and compares this with other virus-insect models.ResultsWhereas MdSGHV is not vertically transmitted, GpSGHV is both vertically and horizontally transmitted, and the balance between the two transmission modes may significantly influence the pathogenesis of tsetse virus. The presence and absence of bacterial symbionts (Wigglesworthia and Sodalis) in tsetse and Wolbachia in the housefly, respectively, potentially contributes to the development of SGH symptoms. Unlike MdSGHV, GpSGHV contains not only host-derived proteins, but also appears to have evolutionarily recruited cellular genes from ancestral host(s) into its genome, which, although may be nonessential for viral replication, potentially contribute to the evasion of host’s immune responses. Whereas MdSGHV has evolved strategies to counteract both the housefly’s RNAi and apoptotic responses, the housefly has expanded its repertoire of immune effector, modulator and melanization genes compared to the tsetse fly.ConclusionsThe ecologies and life-histories of the housefly and tsetse fly may significantly influence coevolution of MdSGHV and GpSGHV with their hosts. Although there are still many unanswered questions regarding the pathogenesis of SGHVs, and the extent to which microbiota influence expression of overt SGH symptoms, SGHVs are attractive ‘explorers’ to elucidate the immune responses of their hosts, and the transmission modes of other large DNA viruses.

Characterization and Tissue Tropism of Newly Identified Iflavirus and Negeviruses in Glossina morsitans morsitans Tsetse Flies

“…A vertical transmission has already been demonstrated in the case of GpSGHV in G. pallidipes [7], which might be associated with the presence of the tsetse symbiont Sodalis [41]. In our study, we confirmed the presence of tsetse symbionts in the milk glands, but further investigations are needed to understand their role in the transmission of GmmIV and GmmNegeV.…”

Cloning and characterization of the histone variant gene H2A.Z in Bombyx mori

“…For example, EBV, MHV68, HIV‐1, and adenovirus infections can induce H2A.X phosphorylation, a process that plays a crucial role in antiviral response and DNA damage repair (Nichols et al, 2009; Mitra et al, 2012). Viruses even modulate the expression of host immune response genes, DNA damage repair genes, and genes related to tumorigenesis by modifying histone proteins and their modifications to thrive and replicate within host cells (Kariithi et al, 2018). Therefore, it is plausible that BmNPV could adopt a chromatin‐like structure by incorporating histones and histones variants.…”

The Insect Pest Control Laboratory of the Joint FAO/IAEA Programme: Ten Years (2010–2020) of Research and Development, Achievements and Challenges in Support of the Sterile Insect Technique

“…The genetic diversity study of the SGHV revealed that the strain detected in G. pallidipes from Tororo, Uganda was the most prevalent strain. Therefore, it appears that G. pallidipes is the most recent tsetse species to be infected with this virus, and it can be speculated that this species is not yet well adapted to a virus infection, which might explain the high prevalence of SGH symptoms and, in certain cases, the collapse of these colonies [ 123 , 168 ].…”