水平基因转移（horizontal gene transfer，HGT），是相对于垂直基因传递（亲代传递给子代）的另一种遗传物质传递方式，是物种进化和基因组革新的重要驱动力之一。水平基因转移现象在原核生物及单细胞真核生物中比较常见，然而，在多细胞的动物中鲜有报道，更不知该机制对动物的进化有着怎样的影响。
在中国科学院昆明动物研究所文建凡研究员和美国东卡罗莱纳大学黄锦苓副教授的共同指导下，硕士研究生倪婷通过全基因组筛选、系统发生分析和结构域分析等方法，首先在较为低等的动物玻璃海鞘（Ciona intestinalis）基因组中鉴定出了92个来自多种藻类的基因，它们隶属于14个基因家族。进一步的调查惊人地发现，原来这些基因普遍存在于不同动物的基因组中。这表明这些基因最有可能是在动物的共同祖先阶段就已经获得。又因这些基因来源于多种不同藻类，因而不太可能是因特定藻类的内共生而转移来的，更可能是动物祖先以多种藻类为食所致。该情形很可能正如著名的进化生物学家Doolittle W.F.（1998）所言：you are what you eat！对这些基因的功能分析结果表明，它们主要与分子转运、细胞调控及甲基化信号等功能密切相关，提示着这些基因的获得可能有助于动物祖先中细胞间的交流从而影响着动物的多细胞化（multicellularity）这一重要的进化进程。总之，该研究不仅首次发现了动物基因组中普遍存在不少早期通过水平基因转移获得的外源基因，而且表明该事件可能对整个动物界的进化产生重要的影响。此外，该研究还为“无质体真核生物中的藻类基因并不都起源于原始质体”的论断提供了额外的证据。该研究成果近期已在“BMC Evolutionary Biology”（DOI 10.1186/1471-2148-12-83）上发表。
本工作得到了国家自然科学基金项目和中国科学院知识创新工程重要方向项目的资助。（生物谷Bioon.com）
doi:10.1186/1471-2148-12-83
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Ancient gene transfer from algae to animals: Mechanisms and evolutionary significance
Ting Ni, Jipei Yue, Guiling Sun, Yong Zou, Jianfan Wen and Jinling Huang
Background Horizontal gene transfer (HGT) is traditionally considered to be rare in multicellular eukaryotes such as animals. Recently, many genes of miscellaneous algal origins were discovered in choanoflagellates. Considering that choanoflagellates are the existing closest relatives of animals, we speculated that ancient HGT might have occurred in the unicellular ancestor of animals and affected the long-term evolution of animals. Results Through genome screening, phylogenetic and domain analyses, we identified 14 gene families, including 92 genes, in the tunicate Ciona intestinalis that are likely derived from miscellaneous photosynthetic eukaryotes. Almost all of these gene families are distributed in diverse animals, suggesting that they were mostly acquired by the common ancestor of animals. Their miscellaneous origins also suggest that these genes are not derived from a particular algal endosymbiont. In addition, most genes identified in our analyses are functionally related to molecule transport, cellular regulation and methylation signaling, suggesting that the acquisition of these genes might have facilitated the intercellular communication in the ancestral animal. Conclusions Our findings provide additional evidence that algal genes in aplastidic eukaryotes are not exclusively derived from historical plastids and thus important for interpreting the evolution of eukaryotic photosynthesis. Most importantly, our data represent the first evidence that more anciently acquired genes might exist in animals and that ancient HGT events have played an important role in animal evolution.
