MLVs

Murine leukemia viruses (MLVs) are a group of gammaretroviruses in the Retroviridae family that infect mice and related rodents. They replicate by reverse transcription and integration into the host genome and exist both as exogenous infectious agents and as endogenous retroviral sequences in the mouse genome.

Exogenous MLVs are historically classified by host range into ecotropic, xenotropic, polytropic, and amphotropic subtypes. Ecotropic MLVs infect mouse cells; xenotropic MLVs infect cells of other species; polytropic and amphotropic MLVs display broader host ranges. These groups reflect differences in receptor usage and entry.

Genomic organization follows the typical retroviral scheme, with gag, pol, and env genes flanked by long terminal repeats. After entry, reverse transcription generates a DNA provirus that integrates into the host genome, enabling persistent expression of viral and transduced sequences.

MLV-based vectors have been used in molecular biology for gene delivery due to stable integration. In early clinical trials, insertional mutagenesis linked to MLV vectors caused malignancies in some patients, leading to redesigned, safer vector systems and increased use of non-integrating approaches and alternative vectors.

Endogenous MLV sequences are widespread in the mouse genome and contribute to genome evolution and regulation. Research continues to clarify their activity and impact on development and disease.