Poster abstracts
Poster number 64 submitted by Khondakar Sayef Ahammed
EXOSC1/Csl4 exosomopathy variants have distinct and overlapping in vivo effects on budding yeast RNA exosome function
Khondakar Sayef Ahammed (Department of Molecular Genetics, Center for RNA Biology, The Ohio State University; Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston), Jaeil Han (Chungnam National University, South Korea), Ambro van Hoof (Department of Molecular Genetics, Center for RNA Biology, The Ohio State University; Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston)
Abstract:
The RNA exosome complex is a major 3’ RNase in eukaryotes that catalyzes the processing and degradation of a wide range of substrates in the nucleus and cytoplasm. Single amino acid mutations in RNA exosome subunits cause a range of Mendelian diseases collectively referred to as exosomopathies. However, distinguishing these disease-causing variants from non-pathogenic ones remains challenging, and the mechanism by which these variants cause disease is largely unknown. We developed a hybrid yeast/mammalian RNA exosome model of exosomopathies by systematically replacing the individual yeast subunits with their corresponding human or mouse orthologs. This allows us to unambiguously assess the damaging effects of the exact patient variant in budding yeast. Functional analysis of the disease-associated variants utilizing this genetic tool revealed defects in RNA exosome function caused by previously known as well as uncharacterized variants in several replaceable subunits, including EXOSC1, EXOSC2, EXOSC4, EXOSC7, and EXOSC9.
Further detailed investigation of the two damaging EXOSC1 variants, using orthologous mutations in the corresponding yeast subunit Csl4, revealed malfunction in the nuclear and cytoplasmic functions of RNA exosome. These two patient-derived mutations are located in functionally redundant domains of Csl4, and each variant partially impaired RNA exosome function by disrupting its corresponding domain. Genetic and transcriptome analysis of these csl4 variants implied that the N- and C-terminal domains of Cs4 have distinct and overlapping in vivo functions. Furthermore, these Csl4 domains maintain a ‘bipartite functional interaction’ with nuclear cofactors (Rrp6, Mpp6, and Mtr4), where one of the interactions is required for the essential function of the exosome. Thus, analyzing disease variants in the budding yeast model provides important insights into RNA exosome defects caused by patient-derived variants and elucidates the subunit-specific role of Csl4/EXOSC1 in nuclear RNA exosome function.
Keywords: RNA exosome complex