Badaraco J L, Ayala F J, Bart J-M, Gottstein B, Haag K L
Programa de Pós Graduação em Genética e Biologia Molecular, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil.
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA.
Exp Parasitol. 2008 Aug;119(4):453-459. doi: 10.1016/j.exppara.2008.02.004. Epub 2008 Feb 19.
Based on the distinctiveness of their mitochondrial haplotypes and other biological features, several recent publications have proposed that some Echinococcus granulosus strains should be regarded as separate species. However, the genetic cohesion of these species has not been extensively evaluated using nuclear markers. We assess the degree of polymorphism of the partial mitochondrial cox1 (366bp), the nuclear mdh (214bp) and EgAgB4 (281-283bp) genes of E. granulosus sensu lato isolates collected from areas where different strains occur sympatrically. Five distinct mitochondrial haplotypes were determined by direct sequencing (G1, G2, G5, G6 and G7). The mdh genotypes were first screened by SSCP: three alleles were identified (Md1-Md3), which were further confirmed by nucleotide sequencing. For EgAgB4, which was analysed by direct sequencing the PCR products, two groups of sequences were found: EgAgB4-1 and EgAgB4-2. No haplotype-specific mdh or EgAgB4 sequences occur. Nevertheless, alleles Md1 and Md2 and type 1 sequences of EgAgB4 showed a higher frequency within the group of haplotypes G1-G2, while allele Md3 and EgAgB4-2 are most frequent in the G5-G7 cluster. By AMOVA it is shown that 79% of the total genetic variability is found among haplotype groups. These findings are compatible with two not mutually exclusive evolutionary hypotheses: (a) that haplotypes share an ancestral polymorphism, or (b) that the reproductive isolation between parasites with distinct haplotypes is not complete, leading to gene introgression. The biologic and epidemiologic consequences of our findings are discussed.
基于线粒体单倍型和其他生物学特征的独特性，最近的几篇出版物提出，一些细粒棘球绦虫菌株应被视为不同的物种。然而，这些物种的遗传凝聚力尚未使用核标记进行广泛评估。我们评估了从不同菌株同域分布地区收集的广义细粒棘球绦虫分离株的部分线粒体细胞色素氧化酶亚基1（cox1，366bp）、核苹果酸脱氢酶（mdh，214bp）和EgAgB4（281 - 283bp）基因的多态性程度。通过直接测序确定了五种不同的线粒体单倍型（G1、G2、G5、G6和G7）。mdh基因型首先通过单链构象多态性（SSCP）进行筛选：鉴定出三个等位基因（Md1 - Md3），并通过核苷酸测序进一步确认。对于通过直接测序PCR产物进行分析的EgAgB4，发现了两组序列：EgAgB4 - 1和EgAgB4 - 2。未出现单倍型特异性的mdh或EgAgB4序列。然而，等位基因Md1和Md2以及EgAgB4的1型序列在单倍型G1 - G2组中频率较高，而等位基因Md3和EgAgB4 - 2在G5 - G7簇中最常见。通过分子方差分析（AMOVA）表明，79%的总遗传变异存在于单倍型组之间。这些发现与两个并非相互排斥的进化假说相符：（a）单倍型共享祖先多态性，或（b）具有不同单倍型的寄生虫之间的生殖隔离不完全，导致基因渗入。我们讨论了这些发现的生物学和流行病学后果。
