Evolutionary origin of a functional gonadotropin in the pituitary of the most primitive vertebrate, hagfish
Evolutionary origin of a functional gonadotropin in the pituitary of the most primitive vertebrate, hagfish
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DOI：
10.1073/pnas.1002208107
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发表时间：
2010-08
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影响因子：
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通讯作者：
K. Uchida;S. Moriyama;H. Chiba;Toyokazu Shimotani;K. Honda;M. Miki;A. Takahashi;S. Sower;M. Nozaki
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文献类型：
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作者：
K. Uchida;S. Moriyama;H. Chiba;Toyokazu Shimotani;K. Honda;M. Miki;A. Takahashi;S. Sower;M. Nozaki
鳗鱼既没有颌骨也没有脊椎骨，被认为是已知的最原始的脊椎动物，要么存活，要么灭绝。鳗鱼长期以来一直是脊椎动物进化的谜团，这不仅是因为它们的进化地位，也是因为我们对基本过程缺乏了解。鳗鱼生殖内分泌系统的关键因素尚未阐明。在这里，一种功能性糖蛋白激素(GPH)的存在和鉴定已经从褐鳗中阐明。鳗鱼GPH由α和β两个亚基组成，这两个亚基是在腺垂体的同一细胞中合成和共存的。鳗鱼GPh、α和-β的细胞活性和转录活性与性腺发育阶段显著相关。纯化的天然GPH体外诱导性类固醇释放。根据系统发育分析，我们认为脊椎动物糖蛋白α亚基2(GPA2)和β亚基5(GPB5)分别导致了GPhα和GPhβ家族。序列分析和系统发育分析表明，所鉴定的八头鳗GPhα和-β亚基为典型的钩口GPhα和-β亚基。我们假设，鳗鱼的单一功能GPH的同一性，为在最早的分叉脊椎动物中存在脑垂体-性腺系统提供了关键证据，该系统可能是由祖先、前脊椎动物特有的神经内分泌机制进化而来的，通过逐渐出现以前未描述的控制水平，即脑垂体，这在原脊椎动物中没有发现。
Hagfish, which lack both jaws and vertebrae, are considered the most primitive vertebrate known, living or extinct. Hagfish have long been the enigma of vertebrate evolution not only because of their evolutionary position, but also because of our lack of knowledge on fundamental processes. Key elements of the reproductive endocrine system in hagfish have yet to be elucidated. Here, the presence and identity of a functional glycoprotein hormone (GPH) have been elucidated from the brown hagfish Paramyxine atami. The hagfish GPH consists of two subunits, α and β, which are synthesized and colocalized in the same cells of the adenohypophysis. The cellular and transcriptional activities of hagfish GPHα and -β were significantly correlated with the developmental stages of the gonad. The purified native GPH induced the release of gonadal sex steroids in vitro. From our phylogenetic analysis, we propose that ancestral glycoprotein α-subunit 2 (GPA2) and β-subunit 5 (GPB5) gave rise to GPHα and GPHβ of the vertebrate glycoprotein hormone family, respectively. The identified hagfish GPHα and -β subunits appear to be the typical gnathostome GPHα and -β subunits based on the sequence and phylogenetic analyses. We hypothesize that the identity of a single functional GPH of the hagfish, hagfish GTH, provides critical evidence for the existence of a pituitary-gonadal system in the earliest divergent vertebrate that likely evolved from an ancestral, prevertebrate exclusively neuroendocrine mechanism by gradual emergence of a previously undescribed control level, the pituitary, which is not found in the Protochordates.