ITS-1 ribosomal DNA sequence variants are maintained in different species and strains of Echinococcus.
This study investigated sequence heterogeneity in the first internal transcribed spacer (ITS-1) of ribosomal DNA within and among species and strains of Echinococcus. Different ITS-1 sequence variants exist in Echinococcus granulosus and Echinococcus multilocularis, which represent at least four evolutionary lineages: (1) a sheep strain-lineage of E. granulosus, (2) a sister lineage of a cervid and camel E. granulosus ITS-1 variants, (3) a lineage including the ITS-1 variants representing horse, bovine and camel strains of E. granulosus, as well as variants from E. multilocularis, Echinococcus oligarthrus and Echinococcus vogeli and (4) a distinct lineage of ITS-1 variants including E. granulosus strains from sheep and cervid, and E. multilocularis. At least two of the species (E. granulosus and E. multilocularis) were paraphyletic for ITS-1. Divergent ITS-1 variants from these two species shared distinct evolutionary lineages. The sequence data provided evidence that at least two turnover mechanisms, namely slippage and unequal crossing over/transposition, have led to the divergence and maintenance of sequence variants in Echinococcus species and strains.
van Herwerden
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Department of Veterinary Science, The University of Melbourne, 250 Princes Highway, Werribee, Australia.
Gasser
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RB
Blair
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D000818:Animals; D001483:Base Sequence; D002162:Camelus; D002417:Cattle; D016384:Consensus Sequence; D018509:DNA, Helminth / Q000737:chemistry*; D004275:DNA, Ribosomal / Q000235:genetics*; D003670:Deer; D004446:Echinococcus / Q000145:classification / Q000235:genetics*; D019143:Evolution, Molecular; D014644:Genetic Variation; D005838:Genotype; D006736:Horses; D008969:Molecular Sequence Data; D012091:Repetitive Sequences, Nucleic Acid; D017422:Sequence Analysis, DNA; D012756:Sheep
D018509:DNA, Helminth; D004275:DNA, Ribosomal