Achaete-scute complex (ASC) genes play essential roles in regulating neurogenesis of metazoans. Various metazoan species have greatly different numbers of genes in ASCa, ASCb and ASCc families. To explore evolutionary mechanisms of metazoan ASC genes, Blast (basic local alignment search tool) searches and phylogenetic analyses were conducted to identify ASC genes in metazoan species and to infer phylogenetic relationship between various ASC genes. As a result, 2784 ASC genes were identified in 804 metazoan species. The phylogenetic tree constructed using 1237 unique bHLH motifs shows that metazoan ASCa, ASCb and ASCc families contain six (a1-a6), five (b1-b5) and three (c1-c3) bHLH genes, respectively. Further phylogenetic analyses suggest that ASC genes in metazoans are derived from a primitive c gene, those in insects are derived from c2 gene, and those in chordates are derived from a2 and a3 genes. Data of gene linkage demonstrate that insect a6 is derived from a4 but not from a5, and chordate a2 is ancestral to b5 only, whilst a3 is ancestral to both b3 and b5. It is concluded that current ASC gene families in metazoans were established through a series of sub- and/or neo-functionalization to duplicated ancestral ASC gene(s). These results provide good references for exploring evolutionary mechanisms of other bHLH genes in metazoans. Besides, gene subtyping is considered as an efficient method for evolutionary studies on closely related homologous genes.

中文翻译：

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系统发育分析的achaete-scute复杂基因的后生动物。

Achaete-scute复杂（ASC）基因在调节后生动物的神经发生中起重要作用。在ASCa，ASCb和ASCc家族中，各种后生动物物种的基因数量差异很大。为了探索后生动物ASC基因的进化机制，进行了Blast（基本局部比对搜索工具）搜索和系统发育分析，以鉴定后生动物物种中的ASC基因，并推断各种ASC基因之间的系统发育关系。结果，在804个后生动物物种中鉴定出2784个ASC基因。用1237个独特的bHLH基序构建的系统树表明，后生动物ASCa，ASCb和ASCc家族分别包含六个（a1-a6），五个（b1-b5）和三个（c1-c3）bHLH基因。进一步的系统发育分析表明，后生动物中的ASC基因源自原始的c基因，昆虫中的ASC基因源自c2基因，那些在和弦中的是从a2和a3基因衍生的。基因连锁的数据表明，昆虫a6源自a4，而不是源自a5，而碳酸盐a2仅起源于b5，而a3同时起源于b3和b5。结论是，通过对复制的祖先ASC基因进行一系列的亚功能和/或新功能化，建立了后生动物中的当前ASC基因家族。这些结果为探索后生动物中其他bHLH基因的进化机制提供了很好的参考。此外，基因分型被认为是对密切相关的同源基因进行进化研究的有效方法。结论是，通过对复制的祖先ASC基因进行一系列的亚功能和/或新功能化，建立了后生动物中的当前ASC基因家族。这些结果为探索后生动物中其他bHLH基因的进化机制提供了很好的参考。此外，基因亚型被认为是对密切相关的同源基因进行进化研究的有效方法。结论是，通过对复制的祖先ASC基因进行一系列的亚功能和/或新功能化，建立了后生动物中的当前ASC基因家族。这些结果为探索后生动物中其他bHLH基因的进化机制提供了很好的参考。此外，基因亚型被认为是对密切相关的同源基因进行进化研究的有效方法。