Three-dimensional visualization of gammaherpesvirus life cycle in host cells by electron tomography

Gammaherpesviruses are etiologically associated with human tumors. A three-dimensional (3D) examination of their life cycle in the host is lacking, significantly limiting our understanding of the structural and molecular basis of virus-host interactions. Here, we report the first 3D visualization of key stages of the murine gammaherpesvirus 68 life cycle in NIH 3T3 cells, including viral attachment, entry, assembly, and egress, by dual-axis electron tomography. In particular, we revealed the transient processes of incoming capsids injecting viral DNA through nuclear pore complexes and nascent DNA being packaged into progeny capsids in vivo as a spool coaxial with the putative portal vertex. We discovered that intranuclear invagination of both nuclear membranes is involved in nuclear egress of herpesvirus capsids. Taken together, our results provide the structural basis for a detailed mechanistic description of gammaherpesvirus life cycle and also demonstrate the advantage of electron tomography in dissecting complex cellular processes of viral infection.