Moriah Szpara

Genomic rearrangements contribute to the enhancement of genetic diversity in populations. However, non-canonical rearrangements (NCRs) such as deletions, insertions, and inversions have the potential to trigger genomic instability. In the case of DNA viruses, NCRs can lead to generation of defective viral genomes (DVGs). To study NCRs in herpes simplex virus type 1 (HSV-1) genomes, we enriched DVGs formation by undiluted serial passaging on various cell types. We found that viral passaging on cell type that enables more viral genomes to initiate replication induces higher amplitude and frequency of cyclic patterns associated with DVGs formation. Despite differences in the rates of DVG accumulation, cell lines displayed comparable quantities of distinct NCRs, indicating that fluctuations caused by DVGs may impose bottlenecks on population genetic diversity. These findings propose additional roles for DVGs in modulating viral genetic diversity. Each cell type exhibited a unique population of NCRs, suggesting that NCRs accumulate in a cell type-specific manner. Interestingly, we identified a higher prevalence of short homologies and short reverse complementary in the parental sequences of NCR junction sites across all cell types. These shared sequence characteristics were also observed in NCRs identified in sequences obtained from clinical samples. The fundamental properties of HSV-1 NCR formation uncovered in this study may have broader implications for other DNA viruses. IMPORTANCE Mutations and genetic rearrangements are the primary driving forces of evolution. Viruses provide valuable model systems for investigating these mechanisms due to their rapid evolutionary rates and vast genetic variability. To investigate genetic rearrangements in the double-stranded DNA genome of herpes simplex virus type 1, the viral population was serially passaged in various cell types. The serial passaging led to formation of defective genomes, resulted from cell-specific non-canonical rearrangements (NCRs). Interestingly, we discovered shared sequence characteristics underlying the formation of these NCRs across all cell types. Moreover, most NCRs identified in clinical samples shared these characteristics. Based on our findings, we propose a model elucidating the formation of NCRs during viral replication within the nucleus of eukaryotic cells.