Data from: Gene conversion yields novel gene combinations in paralogs of GOT1 in the copepod Tigriopus californicus

Background: Gene conversion of duplicated genes can slow the divergence of paralogous copies over time but can also result in other interesting evolutionary patterns. Islands of genetic divergence that persist in the face of gene conversion can point to gene regions undergoing selection for new functions. Novel combinations of genetic variation that differ greatly from the original sequence can result from the transfer of genetic variation between paralogous genes by rare gene conversion events. Genetically divergent populations of the copepod Tigriopus californicus provide an excellent model to look at the patterns of divergence among paralogs across multiple independent evolutionary lineages. Results: In this study the evolution of a set of paralogous genes encoding putative aspartate transaminase proteins (called GOT1 here) are examined in populations of the copepod T. californicus. One pair of duplicated genes, GOT1p1 and GOT1p2, has regions of high divergence between the copies in the face of apparent on-going gene conversion. The GOT1p2 gene also has unique haplotypes in two populations that appear to have resulted from a transfer of genetic variation via inter-paralog gene conversion. A second pair of duplicated genes GOT1Sr and GOT1Sd also shows evidence of gene conversion, but this gene conversion does not appear to have maintained each as a functional copy in all populations. Conclusions: The patterns of conservation and sequence divergence across this set of paralogous genes among populations of T. californicus suggest that some interesting evolutionary patterns are occurring at these loci. The results for the GOT1p1/GOT1p2 paralogs illustrate how gene conversion can factor in the creation of a mosaic pattern of regions of high divergence and low divergence. When coupled with rare gene conversion events of divergent regions, this pattern can result in the formation of novel proteins differing substantially from either original protein. The evolutionary patterns across these paralogs show how gene conversion can both constrain and facilitate diversification of genetic sequences.

研究背景：重复基因的基因转换（gene conversion）可减缓旁系同源拷贝随时间的分化进程，同时也可能催生其他有趣的进化模式。在基因转换作用下仍得以留存的遗传分化岛，可指向正在经历新功能适应性选择的基因区域。罕见的基因转换事件介导旁系同源基因间的遗传变异转移，可形成与原始序列差异极大的全新遗传变异组合。桡足类（copepod）加州猛水蚤（Tigriopus californicus）的遗传分化种群，为研究多个独立进化谱系中旁系同源基因的分化模式提供了极佳的研究模型。
研究结果：本研究针对加州猛水蚤种群中一组编码推定天冬氨酸转氨酶（aspartate transaminase，本文中称为GOT1）的旁系同源基因的进化情况展开分析。其中一对重复基因GOT1p1与GOT1p2，尽管存在持续进行的基因转换现象，但拷贝间仍存在高度分化的区域。GOT1p2基因在两个种群中还存在独特的单倍型（haplotype），这些单倍型似乎是通过旁系同源基因间的基因转换实现遗传变异转移而形成的。另一对重复基因GOT1Sr与GOT1Sd同样存在基因转换的证据，但该基因转换似乎并未使两个拷贝在所有种群中都保持功能完整性。
研究结论：加州猛水蚤种群中这组旁系同源基因的保守性与序列分化模式表明，这些基因位点存在一些有趣的进化现象。GOT1p1/GOT1p2旁系同源基因的研究结果阐明了基因转换如何参与形成高分化区域与低分化区域镶嵌分布的模式。若再结合罕见的分化区域基因转换事件，该模式可催生与任一原始蛋白质差异显著的全新蛋白质。这些旁系同源基因的进化模式揭示了基因转换如何同时制约并推动遗传序列的多样化进程。