Multigene phylogeny of choanozoa and the origin of animals.
Multigene phylogeny of choanozoa and the origin of animals.
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DOI：
10.1371/journal.pone.0002098
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发表时间：
2008-05-07
期刊：
影响因子：
3.7
通讯作者：
Cavalier-Smith T
中科院分区：
文献类型：
--
作者：
Shalchian-Tabrizi K;Minge MA;Espelund M;Orr R;Ruden T;Jakobsen KS;Cavalier-Smith T
动物在进化上与真菌和以单细胞原生动物为主的无尾类动物门，统称为异形类动物有关。为了确定动物从单细胞祖先进化而来的一系列事件，并了解这些关键的进化转变，我们需要确定哪些有节动物与动物关系最密切，以及每个有节动物群体在后生动物系统发育树中的进化位置。在这里，我们关注的是震颤部，一种微小的食菌细胞，有细长的辐射触须。单基因树表明，它要么是动物最接近的单细胞亲戚，要么是传统上被认为可能是动物祖先的脊椎动物的姐妹。对数以千计的部长蛋白基因进行测序，现在发现了大约14个对动物细胞生物学具有关键意义的结构域，包括几个以前从严重分化的有节动物中未知的结构域，例如与Hedgehog、Notch和酪氨酸激酶信号或细胞黏附(钙粘附素)有关的结构域。使用78种蛋白质构建的系统发育树表明，该属不是动物的姐妹动物，也不是脊椎动物的姐妹动物(它们自己也是动物的姐妹)，而是与另一种具有丝状触须的原生动物卡萨斯孢子虫(Capsaspora)。丝虫亚纲(新纲丝虫)是动物和脊椎动物的姊妹门，这三个类群形成了一个新的支系(丝虫)，其祖先可能在纤毛触须聚集为脊椎动物/海绵共同祖先的纤毛项圈之前很久就进化出了纤毛触须。我们的树显示鱼孢子虫是丝虫的姐妹；泛素和核糖体小亚基S30蛋白基因之间的融合统一了所有的全虫(丝虫和鱼孢子虫)，这在早期的分枝真核生物中是不存在的。因此，在动物的多细胞体平面起源之前，它们的单细胞近亲之间发生了几次连续的进化创新。
Animals are evolutionarily related to fungi and to the predominantly unicellular protozoan phylum Choanozoa, together known as opisthokonts. To establish the sequence of events when animals evolved from unicellular ancestors, and understand those key evolutionary transitions, we need to establish which choanozoans are most closely related to animals and also the evolutionary position of each choanozoan group within the opisthokont phylogenetic tree. Here we focus on Ministeria vibrans, a minute bacteria-eating cell with slender radiating tentacles. Single-gene trees suggested that it is either the closest unicellular relative of animals or else sister to choanoflagellates, traditionally considered likely animal ancestors. Sequencing thousands of Ministeria protein genes now reveals about 14 with domains of key significance for animal cell biology, including several previously unknown from deeply diverging Choanozoa, e.g. domains involved in hedgehog, Notch and tyrosine kinase signaling or cell adhesion (cadherin). Phylogenetic trees using 78 proteins show that Ministeria is not sister to animals or choanoflagellates (themselves sisters to animals), but to Capsaspora, another protozoan with thread-like (filose) tentacles. The Ministeria/Capsaspora clade (new class Filasterea) is sister to animals and choanoflagellates, these three groups forming a novel clade (filozoa) whose ancestor presumably evolved filose tentacles well before they aggregated as a periciliary collar in the choanoflagellate/sponge common ancestor. Our trees show ichthyosporean choanozoans as sisters to filozoa; a fusion between ubiquitin and ribosomal small subunit S30 protein genes unifies all holozoa (filozoa plus Ichthyosporea), being absent in earlier branching eukaryotes. Thus, several successive evolutionary innovations occurred among their unicellular closest relatives prior to the origin of the multicellular body-plan of animals.
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