DNA methylation is an epigenetic mark associated with gene regulation and cell memory, silencing of transposable elements, genomic imprinting, and repression of spurious transcription of duplicated sequences. These roles have varied widely during animal evolution and current functions depend on the specific methylation pattern of the species under consideration. The patterns of methylation are established, maintained, and translated into appropriate functional states by the DNA-methylation machinery, which includes three groups of methyltransferase enzymes, Dnmt1, Dnmt2 and Dnmt3, and five methyl-DNA binding proteins, Mbd1, Mbd2, Mbd3, Mbd4, and MeCP2. In this study, I have identified the members of the Dnmt and the Mbd gene families in the cephalochordate amphioxus (Branchiostoma floridae), the most basal extant chordate and one of the closest sister groups of vertebrates. Database searches, phylogenetic studies and protein domain analyses revealed the presence of the three major groups of Dnmt enzymes in the cephalochordate genome, whereas only two Mbd members, Mbd2/3 and Mbd4, were found. Analysis of the amphioxus methylation machinery suggested that the complexity and the structural organization of cephalochordate methyltransferases do not differ substantially from those of current vertebrate enzymes, while new Mbd proteins arose in vertebrates, which perhaps minimized certain collateral effects associated with the major genomic changes that occurred during the invertebrate-vertebrate transition.

中文翻译：

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DNA甲基化机制的演变：佛罗里达文昌鱼分支中的DNA甲基转移酶和甲基DNA结合蛋白。

DNA甲基化是一种表观遗传学标记，与基因调控和细胞记忆，转座因子沉默，基因组印迹以及重复序列的虚假转录抑制相关。这些作用在动物进化过程中变化很大，目前的功能取决于所考虑物种的特定甲基化模式。通过DNA甲基化机制建立，维持并转化甲基化模式，该机制包括三组甲基转移酶Dnmt1，Dnmt2和Dnmt3，以及五种甲基DNA结合蛋白Mbd1，Mbd2，Mbd3， Mbd4和MeCP2。在这项研究中，我确定了头孢类双歧杆菌（Branchiostoma floridae）中Dnmt和Mbd基因家族的成员，现存最基脉的脊椎动物，是脊椎动物中最接近的姐妹群之一。数据库搜索，系统发育研究和蛋白质结构域分析揭示了头孢酸盐基因组中存在三大类Dnmt酶，而仅发现了两个Mbd成员Mbd2 / 3和Mbd4。对两栖动物甲基化机制的分析表明，头孢菌素甲基转移酶的复杂性和结构组织与目前的脊椎动物酶没有实质性差异，而新的Mbd蛋白在脊椎动物中出现，这可能最小化了与发生的主要基因组变化相关的某些附带影响在无脊椎动物向无脊椎动物过渡期间。系统发育研究和蛋白质结构域分析表明，头孢酸盐基因组中存在三大类Dnmt酶，而仅发现了两个Mbd成员Mbd2 / 3和Mbd4。对两栖动物甲基化机制的分析表明，头孢菌素甲基转移酶的复杂性和结构组织与目前的脊椎动物酶没有实质性差异，而新的Mbd蛋白在脊椎动物中出现，这可能使与发生的主要基因组变化相关的某些附带影响最小化在无脊椎动物向无脊椎动物过渡期间。系统发育研究和蛋白质结构域分析表明，头孢酸盐基因组中存在三大类Dnmt酶，而仅发现了两个Mbd成员Mbd2 / 3和Mbd4。对两栖动物甲基化机制的分析表明，头孢菌素甲基转移酶的复杂性和结构组织与目前的脊椎动物酶没有实质性差异，而新的Mbd蛋白在脊椎动物中出现，这可能最小化了与发生的主要基因组变化相关的某些附带影响在无脊椎动物向无脊椎动物过渡期间。