Evans Ben J
Center for Environmental Genomics Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
Genetics. 2007 Jun;176(2):1119-30. doi: 10.1534/genetics.106.069690. Epub 2007 Apr 15.
Allopolyploid species form through the fusion of two differentiated genomes and, in the earliest stages of their evolution, essentially all genes in the nucleus are duplicated. Because unique mutations occur in each ancestor prior to allopolyploidization, duplicate genes in these species potentially are not interchangeable, and this could influence their genetic fates. This study explores evolution and expression of a simple duplicated complex--a heterodimer between RAG1 and RAG2 proteins in clawed frogs (Xenopus). Results demonstrate that copies of RAG1 degenerated in different polyploid species in a phylogenetically biased fashion, predominately in only one lineage of closely related paralogs. Surprisingly, as a result of an early deletion of one RAG2 paralog, it appears that in many species RAG1/RAG2 heterodimers are composed of proteins that were encoded by unlinked paralogs. If the tetraploid ancestor of extant species of Xenopus arose through allopolyploidization and if recombination between paralogs was rare, then the genes that encode functional RAG1 and RAG2 proteins in many polyploid species were each ultimately inherited from different diploid progenitors. These observations are consistent with the notion that ancestry can influence the fate of duplicate genes millions of years after duplication, and they uncover a dimension of natural selection in allopolyploid genomes that is distinct from other genetic phenomena associated with polyploidization or segmental duplication.
异源多倍体物种通过两个分化的基因组融合形成，在其进化的早期阶段，细胞核中的几乎所有基因都会发生复制。由于在异源多倍体化之前每个祖先中都会发生独特的突变，这些物种中的重复基因可能无法互换，这可能会影响它们的遗传命运。本研究探讨了一种简单重复复合体的进化和表达——爪蟾（非洲爪蟾属）中RAG1和RAG2蛋白之间的异二聚体。结果表明，RAG1的拷贝在不同的多倍体物种中以系统发育偏向的方式退化，主要发生在一个密切相关的旁系同源物谱系中。令人惊讶的是，由于一个RAG2旁系同源物的早期缺失，在许多物种中，RAG1/RAG2异二聚体似乎由非连锁旁系同源物编码的蛋白质组成。如果现存非洲爪蟾属物种的四倍体祖先是通过异源多倍体化产生的，并且旁系同源物之间的重组很少见，那么许多多倍体物种中编码功能性RAG1和RAG2蛋白的基因最终分别来自不同的二倍体祖先。这些观察结果与这样一种观点一致，即祖先可以在复制数百万年后影响重复基因的命运，并且它们揭示了异源多倍体基因组中自然选择的一个维度，该维度与多倍体化或片段重复相关的其他遗传现象不同。
