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Updated: Sep 28, 2026
Isolation of Fidelity Variants of RNA Viruses and Characterization of Virus Mutation Frequency
Published on: June 16, 2011
Identification of mutations associated with attenuation of virulence of a field Sendai virus isolate by egg passage
Yutaka Fujii1, Takemasa Sakaguchi, Katsuhiro Kiyotani
1Department of Bacteriology, Hiroshima University School of Medicine, Japan.
Abstract:
Abstract. We have reported that attenuation of the virulence of a field Sendai virus (SeV) isolated by egg passage is associated with an impediment of viral genome replication in mouse respiratory cells (Kiyotani et al., Arch Virol 146, 893-908, 2001). To determine the molecular basis for the attenuation, we sequenced entire genomes of representative SeV clones isolated during egg passages and compared those with that of the parental SeV clone E0. E15c2, a 165-fold attenuated clone in 50% mouse lethal dose (MLD50) isolated at the 15th egg passage, possessed only four mutations in the entire genome: U to A at position 20 (U20A) and U24A in the leader promoter region and A9362G and A12174U in the L gene from the 5'-end of antigenome. The former mutation in the L gene was silent and the latter changed deduced amino acid Ser at position 1207 to Cys (Serl207Cys) in the L protein, a catalytic subunit of viral polymerase. E30c12, a further 6-fold attenuated clone isolated at the 30th egg passage, had an additional four mutations: A8074G (Glu461Gly) and A8077G (Asp462Gly) in the hemagglutinin-neuraminidase (HN) gene and A13598C (silent) and G13927A (Ser1791Asn) in the L gene. On the other hand, a virulent revertant clone, E30M15c15, which was obtained by 15 mouse passages of E30c12 and had 250-fold mouse virulence compared to E30c12, possessed eight mutaions: A24U in the leader, C1325U (silent) in the nucleocapsid gene, G8074A (Gly461Glu) in the HN gene, G10433U (Lys626Asn), C13598A (silent), A13927G (Asn1791Ser), C14626U (Thr2024Ile) and A15272C in the L gene. Among these, the mutations in the leader and the HN gene and two of the mutations in the L gene (C13598A and A13927G) were true reversions to E0. The significance of the mutations detected in the leader as well as in the L and HN genes was discussed in the context of attenuation of SeV pathogenicity by egg passage.
Insights
Egg passage attenuates Sendai virus (SeV) virulence by impacting viral genome replication. Mutations in the leader, L, and hemagglutinin-neuraminidase (HN) genes correlate with reduced SeV pathogenicity, offering insights into viral attenuation mechanisms.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Sendai virus (SeV) virulence attenuation during egg passage is linked to impaired viral genome replication in mouse respiratory cells.
- Understanding the molecular basis of this attenuation is crucial for controlling SeV pathogenicity.
Purpose of the Study:
- To determine the molecular mechanisms underlying SeV attenuation during serial egg passages.
- To identify specific genetic mutations responsible for reduced SeV virulence.
Main Methods:
- Whole-genome sequencing of representative SeV clones isolated during egg passages.
- Comparison of mutated SeV genomes with the parental SeV clone E0.
- Analysis of mutations in the leader promoter, L gene, and hemagglutinin-neuraminidase (HN) gene.
Main Results:
- An attenuated clone (E15c2) showed four mutations, including changes in the leader promoter and L gene (encoding viral polymerase).
- A further attenuated clone (E30c12) acquired additional mutations in the HN and L genes.
- A virulent revertant clone (E30M15c15) exhibited eight mutations, with some representing true reversions to the parental sequence.
Conclusions:
- Specific mutations in the SeV leader, L, and HN genes are associated with reduced pathogenicity.
- These findings elucidate the genetic determinants of SeV attenuation during egg passage.
- The identified mutations provide a molecular basis for understanding SeV virulence and attenuation.
