Molecular characterization of baculovirus-induced chromatin marginalization and architectural alteration

To facilitate rapid replication and assembly of progeny, baculovirus is known to manipulate the host nuclear microenvironment by inducing chromatin changes in localization and architecture. However, the molecular mechanisms underlying these changes remain unknown. Here, we revealed that the nuclear lamina (NL) protein Lamin A/C interacts with the heterochromatin protein 1 alpha (HP1a) and identified the middle region of HP1a as critical for this interaction. Suppression of Lamin A/C and HP1a expression resulted in a significant inhibition of chromatin marginalization mediated by baculovirus infection. Moreover, the heterochromatin modification H3K9me3, which is recognized and bound by HP1a, also participated in the process of chromatin marginalization. Our live-cell imaging and quantitative analysis unveiled a passive function of marginal chromatin, which involves the formation of a physical barrier that impedes the nuclear egress of the nucleocapsids. Furthermore, baculovirus-induced nuclear F-actin altered the steady-state of intranuclear actin pool, thus regulating the nucleosome disassembly. Overall, our findings illustrate the molecular mechanisms dictating chromatin marginalization and structural alterations during baculovirus infection, shedding new light on the potential function of marginalized chromatin in the origin of its biphasic life cycle. Author SummaryIn our previous study, we illustrated the organization and accessibility of chromatin marginalized by baculovirus infection through a combination of ATAC-seq and biochemical assays. Here, we further dissect the molecular mechanism underlying the baculovirus infection induced chromatin marginalization and disassembly. Specifically, baculovirus utilizes the Lamin A/C-HP1a-H3K9me3 axis to mediate chromatin marginalization at the nuclear periphery. When the interaction between Lamin A/C and HP1a is disrupted, the marginalization of chromatin is also affected. Furthermore, our single-virion tracking results indicate that the marginalized chromatin forms a physical barrier, impeding the nuclear export of nucleocapsids at the very late stage of infection. For the changes in chromatin architecture, we propose a model in which baculovirus infection induced nuclear F-actin compromises the dynamics of nuclear actin pool, which in turn promotes chromatin disassembly. Taken together, we provide a comprehensive understanding of molecular mechanism of baculovirus infection induced changes in chromatin localization and organization, which lay the foundation for studies on how DNA viruses manipulate the nuclear microenvironment.