MSc Sami Salminen will present his doctoral research.
TITLE: Herpesvirus infection-induced changes in nuclear structures and chromatin
ABSTRACT: Herpes simplex virus type 1 viral transcription, DNA replication, and nucleocapsid assembly occur within the host cell nucleus. The infection causes extensive nuclear reorganization, including the emergence and expansion of viral replication compartments (VRCs), redistribution of host cell chromatin to the nuclear periphery, and changes in nucleolar morphology. Progeny nucleocapsids accumulate in the VRC and must traverse the nucleoplasm by diffusion to the nuclear envelope for egress. However, it is not understood how relatively large ~125 nm in diameter capsids diffuse through the chromatin network, particularly the marginalized chromatin layer, to gain access to the nuclear envelope. Furthermore, the infection leads to extensive changes in nucleolar composition, and the repurposing of nucleolar proteins is required for viral replication and nuclear egress, but little is known about how virus-induced changes remodel the nucleolar structure and function. To characterize these changes and their effect on the progression of infection and nuclear egress of capsids, we used molecular biology and microscopy techniques, including Global Run-on sequencing, expansion microscopy, soft X-ray tomography, FLIM-FRET, and single-particle tracking of capsids in live cells. Our results indicate that the marginalizing chromatin initially presents a restrictive barrier to capsids, but later in infection virus-induced changes in chromatin architecture facilitate capsid access to the inner nuclear membrane. Importantly, this transport through chromatin was identified as the rate-limiting step in nuclear egress. The cryo-soft X-ray tomography and fluorescence microscopy analyses revealed infection-induced changes in nucleoli density and roughness, as well as time-dependent changes in the distribution of nucleolar proteins fibrillarin, UBF, and nucleophosmin. Altogether, our findings provide a better understanding of the viral life cycle enabling the identification of novel therapeutic drug targets and allowing the development of new strategies for improvements in oncolytic virotherapy.
Welcome!
