Jill Allmendinger, University of Calgary

Jill Allmendinger (1), Mariel Kleer (1), Jennifer A. Corcoran (1) 1. Microbiology, Immunology and Infectious Diseases Department, Arnie Charbonneau Cancer Institute, Robson DNA Science Centre, Snyder Institute for Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada

Expressing & Multiplying

Nuclear speckles (NSs) are membraneless organelles known to promote expression of genes in their proximity by enhancing RNA transcription, processing, and export. They contain polyadenylated RNA, the cellular long non-coding (lnc) RNA MALAT1, and RNA-binding proteins involved in RNA transcription and processing. NSs have a layered structure, with scaffold proteins in the core and RNAs in the outer shell. Although NSs are known to enhance gene expression, the functional significance of their layered organization is unclear. The oncogenic virus Kaposi's sarcoma-associated herpesvirus (KSHV) alters NSs during infection. We recently showed that an abundant GC-rich and repetitive viral transcript, kaposin, is both necessary and sufficient for NS remodeling. Kaposin assembles NSs near the viral genome to boost viral gene expression, an event dependent on two distinct direct repeat regions within the transcript. Several features of kaposin-NSs suggest that their composition is altered. First, NSs during infection are larger, more circular, and reduced in number. Although they retain core NS proteins like SRRM2 and SON, the lncRNA MALAT1 is expelled from kaposin-NSs. Kaposin-NSs also contain at least one KSHV protein, ORF57, and several viral transcripts. Using a combination of approaches including super-resolution microscopy, immunoprecipitation-mass spectrometry and RNA-immunoprecipitation, we aim to precisely define how kaposin-NSs differ in structure and composition from NSs in uninfected cells. This work will reveal how kaposin remodels NSs to optimize viral gene expression and replication and provide new insight into the functional significance of the layered architecture of NSs.