Phylogenomics meets neuroscience: how many times might complex brains have evolved?
Phylogenomics meets neuroscience: how many times might complex brains have evolved?
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DOI：
10.1556/abiol.63.2012.suppl.2.1
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发表时间：
2012
影响因子：
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通讯作者：
Moroz LL
中科院分区：
文献类型：
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作者：
Moroz LL
复杂的集中式大脑的起源是动物历史上主要的进化转变之一。单系（即在斑藻中存在集中神经系统）与多系（即多个谱系内神经系统平行集中的多重起源）是解释这种转变的两个历史上相互矛盾的场景。然而，最近的系统发育和分支分析表明，复杂的大脑可能在不同的动物谱系中独立进化了至少 9 次。事实上，即使在软体动物门内，头化也可能发生过至少 5 次。新出现的分子数据进一步表明，在基因组水平上，这种转变可能是通过改变少数转录因子的表达来实现的——这并不奇怪，因为这样的事件可能在动物进化的 7 亿年中多次发生。分支和基因组分析也表明神经元本身进化了不止一次。祖先的极化分泌细胞可能参与早期动物纤毛运动的协调，这些细胞可以被认为是不同谱系内神经元的进化前体。在这种情况下，神经元的起源可以与以分泌信号肽作为早期神经递质的整合再生型细胞反应的形式对应激/损伤因素的适应联系起来。为了进一步重建神经系统的平行进化，基因组方法对于探测基底后生动物、选定的冠轮动物（例如拟肢动物、腕足动物）和后口动物的神秘神经元至关重要。
The origin of complex centralized brains is one of the major evolutionary transitions in the history of animals. Monophyly (i.e. presence of a centralized nervous system in urbilateria) vs polyphyly (i.e. multiple origins by parallel centralization of nervous systems within several lineages) are two historically conflicting scenarios to explain such transitions. However, recent phylogenomic and cladistic analysis suggests that complex brains may have independently evolved at least 9 times within different animal lineages. Indeed, even within the phylum Mollusca cephalization might have occurred at least 5 times. Emerging molecular data further suggest that at the genomic level such transitions might have been achieved by changes in expression of just a few transcriptional factors – not surprising since such events might happen multiple times over 700 million years of animal evolution. Both cladistic and genomic analyses also imply that neurons themselves evolved more than once. Ancestral polarized secretory cells were likely involved in coordination of ciliated locomotion in early animals, and these cells can be considered as evolutionary precursors of neurons within different lineages. Under this scenario, the origins of neurons can be linked to adaptations to stress/injury factors in the form of integrated regeneration-type cellular response with secretory signaling peptides as early neurotransmitters. To further reconstruct the parallel evolution of nervous systems genomic approaches are essential to probe enigmatic neurons of basal metazoans, selected lophotrochozoans (e.g. phoronids, brachiopods) and deuterostomes.