The endogenous ecotropic murine retroviruses Emv-16 and Emv-17 are both capable of producing new proviral insertions in the mouse genome

Retroviral elements and their hosts: insertional mutagenesis in the mouse germ line

The inbred mouse is an invaluable model for human biology and disease. Nevertheless, when considering genetic mechanisms of variation and disease, it is important to appreciate the significant differences in the spectra of spontaneous mutations that distinguish these species. While insertions of transposable elements are responsible for only approximately 0.1% of de novo mutations in humans, the figure is 100-fold higher in the laboratory mouse. This striking difference is largely due to the ongoing activity of mouse endogenous retroviral elements. Here we briefly review mouse endogenous retroviruses (ERVs) and their influence on gene expression, analyze mechanisms of interaction between ERVs and the host cell, and summarize the variety of mutations caused by ERV insertions. The prevalence of mouse ERV activity indicates that the genome of the laboratory mouse is presently behind in the "arms race" against invasion.

Interactions between Exogenous and Endogenous Retroviruses

Retroviruses are distinguished from other viruses by several features. Notably, some retroviruses are present as normal elements in the genomes of virtually all vertebrates (endogenous proviruses). Others are exogenous, i.e. horizontally transmitted agents, many of which cause fatal diseases. The endogenous retroviruses are genetically transmitted and to a large extent their significance is uncertain. However, there is evidence suggesting that they contribute to the development of diseases in several animal species. Most importantly, some endogenous retroviruses are capable of interacting with exogenous counterparts through a variety of different mechanisms with serious consequences to the host. Conversely, others are advantageous in that they protect against exogenous retroviruses. In this review various types of interactions between endogenous and exogenous retroviruses are discussed, including receptor interference, recombination, phenotypic mixing, immunological interactions and heterologous trans-activation. Copyright 1997 S. Karger AG, Basel