Moroz L L
The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Blvd. St. Augustine Florida 32080, USA.
Acta Biol Hung. 2012;63 Suppl 2(0 2):3-19. doi: 10.1556/ABiol.63.2012.Suppl.2.1.
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.
复杂集中式大脑的起源是动物历史上主要的进化转变之一。单系起源（即原口动物中存在集中式神经系统）与多系起源（即几个谱系内通过神经系统的平行集中化而多次起源）是解释此类转变的两种历史上相互冲突的假说。然而，最近的系统发育基因组学和分支系统学分析表明，复杂大脑可能在不同动物谱系中至少独立进化了9次。事实上，即使在软体动物门内，头部化也可能至少发生了5次。新出现的分子数据进一步表明，在基因组水平上，此类转变可能仅通过少数转录因子表达的变化就得以实现——这并不奇怪，因为在超过7亿年的动物进化过程中，此类事件可能发生多次。分支系统学和基因组分析都还暗示，神经元本身不止一次进化。祖先的极化分泌细胞可能在早期动物的纤毛运动协调中发挥作用，这些细胞可被视为不同谱系中神经元的进化前体。在这种情况下，神经元的起源可以与以整合的再生型细胞反应形式对应激/损伤因素的适应联系起来，其中分泌信号肽作为早期神经递质。为了进一步重建神经系统的平行进化，基因组方法对于探究基础后生动物、选定的触手冠动物（如帚虫、腕足动物）和后口动物中神秘的神经元至关重要。
