From Cellular Models to In Vivo Insights on Viral Nuclear Import and Post-Nuclear Entry

Viruses that access the nucleus must navigate the highly regulated barrier of the nuclear envelope via the nuclear pore complex (NPC), a dynamic structure whose size and properties have been recently redefined. Once inside, many viruses exploit the host's nuclear environment to complete critical steps of their life cycle, including reverse transcription, integration, and gene expression. This review explores the evolving understanding of viral nuclear import and post-nuclear entry events, highlighting key insights gained from both cellular models and in vivo systems. We focus particularly on HIV-1, whose capsid plays an active and revolutionary role in nuclear entry and post-nuclear entry processes, including the formation of virus-induced biomolecular condensates, novel nuclear compartments that facilitate canonical reverse transcription and integration. This review underscores the importance of combining structural biology, imaging technologies, and in vivo models to reveal the spatiotemporal logic of nuclear events in viral replication.