From cell surface to the nucleus, a short but critical journey for retroviruses

From the cell surface to the nucleus, retroviruses will face multiple obstacles, crossing physical barriers such as the plasma membrane, but also finding their pathway through a viscous cytoplasm. At the same time, retroviruses have to overcome cellular defenses, interfering with the early steps of the virus life cycle. Although the general outcomes of this journey have been known for several decades, the stepwise interactions taking place between cellular and viral factors, which will transform the incoming viral RNA genome into a double-stranded DNA competent for integration, remain largely unknown. In this sense, the uncoating process and the molecular basis of intracellular trafficking of preintegration complexes are still poorly defined. Additionally, other key stages, which have been the focus of many reports, still require some clarification, as is the case for the precise implication of viral and cellular determinants involved in nuclear import of preintegration complexes.