Origin and evolutionary process of the CNS elucidated by comparative genomics analysis of planarian ESTs
Origin and evolutionary process of the CNS elucidated by comparative genomics analysis of planarian ESTs
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DOI：
10.1073/pnas.1332513100
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发表时间：
2003-06-24
影响因子：
11.1
通讯作者：
Gojobori, T
中科院分区：
文献类型：
--
作者：
Mineta, K;Nakazawa, M;Gojobori, T
在双侧动物中，在后口和原口中都发现了一个集中的神经系统。要解决中枢神经系统是否起源于后口动物和原口动物的共同祖先的问题，必须了解在假定的共同祖先的中枢神经系统中存在的基因种类，并追踪中枢神经系统中表达的基因的进化分歧。为了回答这些问题，我们采取了比较的方法，使用不同的物种，特别是集中在较低的双边动物之一，Planarian（扁形动物，Tricladida），这是已知的拥有中枢神经系统。我们测定了涡虫头部EST的核苷酸序列，获得了3,101个非冗余EST克隆。作为同源性搜索的结果，我们发现116个克隆与已知的神经系统相关基因具有显著的相似性。在这里，我们将这116个涡虫EST克隆与人类、果蝇和线虫的完整基因组序列的所有ORF进行了比较，结果表明，这116个神经系统相关基因中的95%以上，包括涉及脑或神经形态发生的基因，在这些生物中是共同的，从而在分子水平上为共同祖先CNS的存在提供了证据。有趣的是，我们发现在不具有神经系统的拟南芥和酵母中，大约有30%的涡虫神经系统相关基因具有同源序列。这意味着神经系统相关基因的起源大大早于神经系统的出现，并且这些基因可能已经被招募到神经系统中。
Among the bilateral animals, a centralized nervous system is found in both the deuterostome and protostome. To address the question of whether the CNS was derived from a common ancestor of deuterostomes and protostomes, it is essential to know kinds of genes existed in the CNS of the putative common ancestor and to trace the evolutionary divergence of genes expressed in the CNS. To answer these questions, we took a comparative approach using different species, particularly focusing on one of the lower bilateral animals, the planarian (Platyhelminthes, Tricladida), which is known to possess a CNS. We determined the nucleotide sequence of ESTs from the head portion of planarians, obtaining 3,101 nonredundant EST clones. As a result of homology searches, we found that 116 clones had significant similarity to known genes related to the nervous system. Here, we compared these 116 planarian EST clones with all ORFs of the complete genome sequences of the human, fruit fly, and nematode, and showed that >95% of these 116 nervous system-related genes, including genes involved in brain or neural morphogenesis, were commonly shared among these organisms, thus providing evidence at the molecular level for the existence of a common ancestral CNS. Interestingly, we found that approximate to30% of planarian nervous system-related genes had homologous sequences in Arabidopsis and yeast, which do not possess a nervous system. This implies that the origin of nervous system-related genes greatly predated the emergence of the nervous system, and that these genes might have been recruited toward the nervous system.