Summary auto-generated
This study analyzed genetic diversity in 109 group A rotavirus samples (serotypes G1 and G4) isolated in Finland during 1986-1990 by phylogenetic analysis of genome segments 4 and 9, which encode proteins VP4 and VP7 that determine P and G serotypes. Nearly all G1 strains and all but one G4 strain showed P[8] specificity. Segment 9 sequences divided G1P[8] strains into four distinct phylogenetic lineages (VP7-G1-1 through VP7-G1-4), while G4P[8] strains formed a single lineage. Segment 4 sequences revealed three P[8] lineages, with G1 and G4 strains mixing between the two main lineages, suggesting independent reassortment of these segments. Globally distributed strains from the 1970s onwards co-clustered with these lineages, indicating they represent stable evolutionary groups. Short amino acid signature motifs uniquely identified each lineage: nine specific amino acids in VP7 positions 29-68 for G1 strains and four in VP4 positions 121-135 for P[8] strains. No linear nucleotide accumulation occurred during the study period; instead, minor e-types formed clusters around predominant strains with slight sequence variations.
Key findings
- G1 and G4 rotaviruses segregated into multiple stable phylogenetic lineages based on segments 4 and 9, with G1P[8] forming four distinct VP7 lineages and three VP4 lineages, while G4P[8] formed one VP7 lineage but two VP4 lineages
- Short amino acid signature motifs (9 residues in VP7 and 4 in VP4) were sufficient to accurately define and distinguish phylogenetic lineages
- Global rotavirus strains from decades earlier clustered with contemporary Finnish isolates in the same lineages, suggesting these lineages have remained relatively stable over time
- G1 and G4 strains mixed freely in P[8] phylogenetic lineages, indicating independent evolution and frequent reassortment of genome segments 4 and 9
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Abstract
Genetic diversity in strains of human group A rotaviruses was analysed by phylogenetic methods. The study material comprised 109 serotype G1 or G4 rotavirus samples isolated in Finland during 1986-1990. Parts of the coding regions of rotaviral genome segments 4 and 9, which encode proteins with serotype specificity, the spike protein VP4 (P serotype) and the outer capsid protein VP7 (G serotype), respectively, were sequenced. As determined by analysis of segment 4 sequences all G1 strains and all except one G4 strain showed P[8] specificity, the one being of P[6] specificity. The G1P[8] strains could be further differentiated into four groups based on segment 9 sequences, while G4P[8] strains formed only one group. Type P[8] (G1P[8] and G4P[8]) strains formed two main groups based on segment 4 sequences, suggesting free segregation of segment 4 between these G strains. Most global G1, G4 and P[8] strains in GenBank/EMBL originating from the 1970s to the present co-clustered with these groups, suggesting that the groups exist as relatively stable lineages. No linear accumulation of nucleotide substitutions was detected in strains of one serotype during the study period. Also, the deduced amino acids of the antigenic regions A, B and C of VP7 were nearly conserved within the phylogenetic lineages. Interestingly, only short amino acid sequences were necessary to divide the e-types correctly into phylogenetic lineages. These amino acid signature motifs were located in aa 29-68 of VP7 and aa 121-135 of VP4 of the G1 and P[8] lineages, respectively.