背景:SARS-CoV-2变体的出现与传播性和毒力增加相关的突变是安大略省的公共卫生问题,加拿大。描述SARS-CoV-2基因组的突变模式如何随时间变化,可以揭示驱动因素,包括增加适应性和宿主免疫反应的选择,这可能有助于新变体的出现。此外,在安大略省的缩影中对SARS-CoV-2的研究,加拿大可以揭示随着时间的推移,不同省份特定的公共卫生政策如何与观察到的突变模式作为模型系统相关联。
目的:本研究旨在对单碱基取代(SBS)类型进行综合分析,计数,以及在安大略省采样的SARS-CoV-2基因组序列中观察到的基因组位置,加拿大。在主要公共卫生事件界定的4个不同时期采样的序列之间进行了突变模式的比较,以跟踪SARS-CoV-2突变景观在2年内的演变。
方法:总共,在安大略省采样的24,244SARS-CoV-2基因组序列和相关元数据,加拿大从2020年1月1日至2021年12月31日从全球共享所有流感数据倡议数据库中检索。根据采样日期,将序列分配给由重大公共卫生事件界定的4个时期。相对于MN996528.1参考基因组鉴定来自每个SARS-CoV-2序列的SBS。生成SBS类型和计数的目录,以估计每个开放阅读框中选择的影响,并识别突变簇。使用Augur管道进行随时间变化的突变适合度的估计。
结果:所观察到的SBS类型和比例的偏差支持先前关于宿主抗病毒防御活性涉及SARS-CoV-2基因组的报道。在历元4期间独特地观察到与腺苷脱氨酶作用于RNA(ADAR)活性相关的U>C取代增加。在SARS-CoV-2基因组序列中观察到的新型SBS的负担在纪元2中最大(中位数为5),其次是时代3(中位数4)。在刺突蛋白开放阅读框中观察到SBS簇,ORF1a,ORF3a在纪元4中,非同义SBS的高比例和dN/dS度量(给定开放阅读框中的非同义突变与同义突变的比率)增加到高于1,表明对刺突蛋白开放阅读框的正向选择。
结论:安大略省微观世界中SARS-CoV-2基因组突变模式的定量分析,在大流行的早期连续时期内,加拿大在公共卫生事件的背景下跟踪了突变动态,这些事件引发了选择和诱变的重大变化。对紧急变异的持续基因组监测将有助于设计公共卫生政策,以应对不断发展的COVID-19大流行。
BACKGROUND: The emergence of SARS-CoV-2 variants with mutations associated with increased transmissibility and virulence is a public health concern in Ontario, Canada. Characterizing how the mutational patterns of the SARS-CoV-2 genome have changed over time can shed light on the driving factors, including
selection for increased fitness and host immune response, that may contribute to the emergence of novel variants. Moreover, the study of SARS-CoV-2 in the microcosm of Ontario, Canada can reveal how different province-specific public health policies over time may be associated with observed mutational patterns as a model system.
OBJECTIVE: This study aimed to perform a comprehensive analysis of single base substitution (SBS) types, counts, and genomic locations observed in SARS-CoV-2 genomic sequences sampled in Ontario, Canada. Comparisons of mutational patterns were conducted between sequences sampled during 4 different epochs delimited by major public health events to track the evolution of the SARS-CoV-2 mutational landscape over 2 years.
METHODS: In total, 24,244 SARS-CoV-2 genomic sequences and associated metadata sampled in Ontario, Canada from January 1, 2020, to December 31, 2021, were retrieved from the Global Initiative on Sharing All Influenza Data database. Sequences were assigned to 4 epochs delimited by major public health events based on the sampling date. SBSs from each SARS-CoV-2 sequence were identified relative to the MN996528.1 reference genome. Catalogues of SBS types and counts were generated to estimate the impact of
selection in each open reading frame, and identify mutation clusters. The estimation of mutational fitness over time was performed using the Augur pipeline.
RESULTS: The biases in SBS types and proportions observed support previous reports of host antiviral defense activity involving the SARS-CoV-2 genome. There was an increase in U>C substitutions associated with adenosine deaminase acting on RNA (ADAR) activity uniquely observed during Epoch 4. The burden of novel SBSs observed in SARS-CoV-2 genomic sequences was the greatest in Epoch 2 (median 5), followed by Epoch 3 (median 4). Clusters of SBSs were observed in the spike protein open reading frame, ORF1a, and ORF3a. The high proportion of nonsynonymous SBSs and increasing dN/dS metric (ratio of nonsynonymous to synonymous mutations in a given open reading frame) to above 1 in Epoch 4 indicate positive
selection of the spike protein open reading frame.
CONCLUSIONS: Quantitative analysis of the mutational patterns of the SARS-CoV-2 genome in the microcosm of Ontario, Canada within early consecutive epochs of the pandemic tracked the mutational dynamics in the context of public health events that instigate significant shifts in
selection and mutagenesis. Continued genomic surveillance of emergent variants will be useful for the design of public health policies in response to the evolving COVID-19 pandemic.