Transmission, Evolution, and Endogenization: Lessons Learned from Recent Retroviral Invasions

Abstract

Viruses of the subfamily are defined by the ability to reverse transcribe an RNA genome into DNA that integrates into the host cell genome during the intracellular virus life cycle. Exogenous retroviruses (XRVs) are horizontally transmitted between host individuals, with disease outcome depending on interactions between the retrovirus and the host organism. When retroviruses infect germ line cells of the host, they may become endogenous retroviruses (ERVs), which are permanent elements in the host germ line that are subject to vertical transmission. These ERVs sometimes remain infectious and can themselves give rise to XRVs. This review integrates recent developments in the phylogenetic classification of retroviruses and the identification of retroviral receptors to elucidate the origins and evolution of XRVs and ERVs. We consider whether ERVs may recurrently pressure XRVs to shift receptor usage to sidestep ERV interference. We discuss how related retroviruses undergo alternative fates in different host lineages after endogenization, with koala retrovirus (KoRV) receiving notable interest as a recent invader of its host germ line. KoRV is heritable but also infectious, which provides insights into the early stages of germ line invasions as well as XRV generation from ERVs. The relationship of KoRV to primate and other retroviruses is placed in the context of host biogeography and the potential role of bats and rodents as vectors for interspecies viral transmission. Combining studies of extant XRVs and "fossil" endogenous retroviruses in koalas and other Australasian species has broadened our understanding of the evolution of retroviruses and host-retrovirus interactions.

Disrupting MLV integrase:BET protein interaction biases integration into quiescent chromatin and delays but does not eliminate tumor activation in a MYC/Runx2 mouse model

“…Murine gammaretroviruses are classified based on their exogenous versus endogenous localization and receptor usage [22,23]. Inbred strains of mice harbor endogenous type C MLVs, which fall into three general classes depending on their receptor usage, and thus their host and tissue specificities.…”

“…Inbred strains of mice harbor endogenous type C MLVs, which fall into three general classes depending on their receptor usage, and thus their host and tissue specificities. These classes include the ecotropic viruses, limited to rodents (mCAT1 receptor), xenotropic viruses (excluded from infection of inbred mice [22]; Xpr1 phosphate exporter receptor), and polytropic/mixed polytropic viruses [24], infecting mouse and nonrodent species [22,23] using Xpr1 as their receptor [25]. Although many endogenous ecotropic and some xenotropic viruses can form infectious particles, the endogenous polytropic MLVs (P-MLVs) do not produce replication competent viruses [22].…”

A viral metagenomic analysis reveals rich viral abundance and diversity in mosquitoes from pig farms

“…Identification and characterization of these non‐classified viruses present in mosquitoes may yield interesting insights into the evolutionary history of other clinically important groups of viruses. Furthermore, as viruses have extraordinary mutation potential, which can lead to the emergence of new vertebrate diseases (Greenwood, Ishida, O'Brien, Roca, & Eiden, ; Kretova et al, ; Sanjuán, Nebot, Chirico, Mansky, & Belshaw, ), the discovery and surveillance of presently harmless strains thus can help to prevent future outbreaks.…”

X-ray Structures of the Post-fusion 6-Helix Bundle of the Human Syncytins and their Functional Implications

“…and the fusion trigger is the interaction with their cellsurface receptor (reviewed in Ref. [59]). In this sense, they are more like the beta-type HIV-1 Env protein, which similarly drives fusion of the viral envelope with the plasma membrane for entry.…”