Spatiotemporal analysis of de novo KSHV infection using Crispr/Cas9-based 3D live cell imaging at single episome resolution

Kaposi Sarcoma-associated herpesvirus (KSHV) persists as a latent episome in infected cells. While the virus efficiently infects established cell lines and primary cells in vitro, the early events guiding establishment of latent infection and the dynamic interplay between viral episomes and host factors remain incompletely understood. Here, we describe the development and application of a CRISPR/Cas9-based 3D live cell imaging system capable of tracking single KSHV episomes in real-time. Our approach exploits the SunTag technology, wherein deactivated Cas9 (dCas9) molecules are fused to repetitive epitope arrays recognized by superfolder GFP-fused single-chain antibodies. By targeting these complexes to terminal repeat units of KSHV, we achieve high level signal amplification, allowing us not only to detect newly incoming viral genomes within the first hours of de novo infection, but also to follow their spatiotemporal trajectories through different stages of the viral lifecycle. Furthermore, to facilitate efficient generation of stable reporter cell lines, we adapted the transposon-based piggyBac system to combine all SunTag components into a single-vector targeting system (SunSeT). Using these systems, we demonstrate the ability to observe both transient and stable interactions between KSHV episomes and key cellular regulators, including the variant polycomb-repressive complex 1 (vPRC) component KDM2B and the innate immune sensor IFI16. Furthermore, our platform allows detailed visualization of episodic changes in episome localization, abundance and distribution during de novo and long-term infection, providing critical insights into how viral genome positioning and dynamics correlate with host subnuclear environments. Overall, our study introduces a robust and adaptable imaging platform to dissect the earliest events of KSHV infection. The ability to track viral episomes in living cells offers a powerful tool to advance our understanding of the spatial and temporal regulation of individual KSHV genomes, shedding light on fundamental mechanisms of herpesvirus latency and persistence.