Key result
cDNA-derived recombinant mumps viruses acquire stable clusters of predominantly synonymous mutations during cell culture passage.
Why the study?
Recombinant mumps viruses with clustered mutations and their stability during passage in cell lines have not been characterized and the mechanisms underlying these phenomena remain unclear.
Recombinant mumps viruses can acquire unusually stable, clustered synonymous mutations during reverse genetics experiments, the mechanism of which remains unknown.
May warrant caution in mumps reverse-genetics experiments; leaves open mechanisms and in vivo relevance.
In reverse genetic experiments we have isolated recombinant mumps viruses (rMuV) that carry large numbers of mutations clustered in small parts of their genome, which are not caused by biased hyper-mutation. In two separate experiments we obtained such recombinant viruses: one virus had 11 mutations in the V/P region of the genome; the other, which also contained an extra transcription unit encoding green fluorescent protein (EGFP), had 32 mutations in the N gene. These specific sets of mutations have not been observed in naturally occurring MuV isolates. Unusually, the vast majority of the mutations (48/51) were synonymous. On passage in Vero cells and human B-LCL cells, a B lymphocyte-like cell line, these mutations appear stable as no reversion occurred to the original consensus sequence, although mutations in other parts of the genome occurred and changed in frequency during passage. Defective interfering RNAs accumulate in passage in Vero cells but not in B-LCL cells. Interestingly, in all passaged samples the level of variation in the EGFP gene is the same as in the viral genes, though it is unlikely that this gene is under any functionality constraint. What mechanism gave rise to these viruses with clustered mutations and their stability remains an open question, which is likely of interest to a wider field than mumps reverse genetics.
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Bamford et al. (2019) studied Mumps virus. Recombinant mumps viruses (rMuV) vs. Original consensus sequence mumps virus was evaluated on Genetic stability of clustered mutations upon passage. Recombinant mumps viruses generated from cDNA clones acquired unusual clusters of predominantly synonymous mutations that remained stable without reverting to the original consensus sequence during repeated passage in cell culture.
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