The discovery of endogenous retroviruses

Abstract

When endogenous retroviruses (ERV) were discovered in the late 1960s, the Mendelian inheritance of retroviral genomes by their hosts was an entirely new concept. Indeed Howard M Temin's DNA provirus hypothesis enunciated in 1964 was not generally accepted, and reverse transcriptase was yet to be discovered. Nonetheless, the evidence that we accrued in the pre-molecular era has stood the test of time, and our hypothesis on ERV, which one reviewer described as 'impossible', proved to be correct. Here I recount some of the key observations in birds and mammals that led to the discovery of ERV, and comment on their evolution, cross-species dispersion, and what remains to be elucidated.

Figure 1

Phylogeny of Retroviruses: genera that include endogenous genomes are marked with an asterisk.

Figure 2

Exogenous and endogenous modes of transmission of ALV.

Figure 3

Exit from and entry into host genomes: transmission of the baboon ERV, BaEV to become the feline ERV, RD114.

Figure 4

Co-evolution and cross-species infection of MLV-related genomes among mammals. Host and retroviral phylogenies are shown on the left and right respectively. Horizontal links indicate co-evolution, whereas sloping links show cross-species infection across large host taxa. Thus two closely related retroviruses infect an ape (gibbon) and a marsupial (koala), and two closely related ERV genomes are found in a carnivore (fox) and a ruminant (sheep). Adapted from Martin et al. [79].