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. 2005 Dec;79(24):15503-10.
doi: 10.1128/JVI.79.24.15503-15510.2005.

Phylogenetic incongruence among oncogenic genital alpha human papillomaviruses

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Phylogenetic incongruence among oncogenic genital alpha human papillomaviruses

Apurva Narechania et al. J Virol. 2005 Dec.

Abstract

The human papillomaviruses (HPVs) have long been thought to follow a monophyletic pattern of evolution with little if any evidence for recombination between genomes. On the basis of this model, both oncogenicity and tissue tropism appear to have evolved once. Still, no systematic statistical analyses have shown whether monophyly is the rule across all HPV open reading frames (ORFs). We conducted a taxonomic analysis of 59 mucosal/genital HPVs using whole-genome and sliding-window similarity measures; maximum-parsimony, neighbor-joining, and Bayesian phylogenetic analyses; and localized incongruence length difference (LILD) analyses. The algorithm for the LILD analyses localized incongruence by calculating the tree length differences between constrained and unconstrained nodes in a total-evidence tree across all HPV ORFs. The process allows statistical evaluation of every ORF/node pair in the total-evidence tree. The most significant incongruence was observed at the putative high-risk (i.e., cancer-associated) node, the common oncogenic ancestor for alpha HPV species 9 (e.g., HPV type 16 [HPV16]), 11, 7 (e.g., HPV18), 5, and 6. Although these groups share early-gene homology, including high degrees of similarity among E6 and E7, groups 9 and 11 diverge from groups 7, 5, and 6 with respect to L2 and L1. The HPV species groups primarily associated with cervical and anogenital cancers appear to follow two distinct evolutionary paths, one conferred by the early genes and another by the late genes. The incongruence in the genital HPV phylogeny could have occurred from an early recombination event, an ecological niche change, and/or asymmetric genome convergence driven by intense selection. These data indicate that the phylogeny of the oncogenic HPVs is complex and that their evolution may not be monophyletic across all genes.

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Figures

FIG. 1.
FIG. 1.
Total-evidence phylogeny. A phylogenetic tree was inferred from maximum-parsimony, neighbor-joining, and Bayesian methods. The tree shown is from the Bayesian analysis inferred from alignment of protein and nucleotide sequences of six concatenated ORFs (E6, E7, E1, E2, L2, and L1). Numbers on or near branches indicate first the node number and after the colon support indices from methods in the following order: Bayesian credibility value, maximum-parsimony bootstrap percentage, and neighbor-joining bootstrap percentage. Methods that show 100% support are represented with an asterisk. Any conflict between the Bayesian tree and either of the other two methods is indicated by an “N” at the appropriate node. Only informative sites were kept for the analyses. Bovine PV type 1 (BPV1) was used as the outgroup taxon.
FIG. 2.
FIG. 2.
Early- and late-gene phylogenies. Phylogenetic trees were inferred using Bayesian methods. The early tree (A) was calculated from E6, E7, E1, and E2 concatenated nucleotide alignments, while the late tree (B) was derived from combined L2 and L1 nucleotide sequence data. Bayesian credibility values are provided near the appropriate nodes, and alpha papillomavirus group designations are shown on their respective leaf branches. A representative virus was chosen from each of 13 alpha HPV species groups (5).
FIG. 3.
FIG. 3.
Open reading frame scans. The frame of the phylogenetic tree and its species groups displayed in Fig. 1 are presented alongside plots of percent identity calculated from global pairwise alignments. The behavior of species group 7 viruses differs with respect to E6 (A) and L2 (B). A common shared homology in E6 appears to be broken in L2.
FIG. 4.
FIG. 4.
Sliding-window analysis. The pairwise distances of HPV18 (A) and HPV16 (B) relative to HPVs selected for Fig. 2 are plotted for comparison. The analysis employed a 500-nucleotide window sliding 20 positions at a time. Arrows emphasize positions of interest, indicating two E6/E7 populations of viruses corresponding to high- and low-risk viruses and the L2 N terminus that displays two populations in the HPV18 scan, but not in the HPV16 scan.
FIG. 5.
FIG. 5.
Localized incongruence length difference analysis. The LILD distributions for all node/partition pairs considered significant at a P of 0.01 are shown. Node numbers correspond to those given in Fig. 1. The full distribution (both the test partition and random partitions greater than zero) for each significant pair is given in order to visualize the relative extent of incongruence from each calculation. The node/partition pairs of particular interest are highlighted with arrows: 4/L2 (arrow 1) and 4/L1 (arrow 2).

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