Conserved keratin gene clusters in ancient fish: An evolutionary seed for terrestrial adaptation
Conserved keratin gene clusters in ancient fish: An evolutionary seed for terrestrial adaptation
复制标题
DOI：
10.1016/j.ygeno.2020.11.008
复制
发表时间：
2021-01-25
期刊：
影响因子：
4.4
通讯作者：
Nikaido, Masato
中科院分区：
文献类型：
--
作者：
Kimura, Yuki;Nikaido, Masato
I型和II型角蛋白是中间丝蛋白的亚类，为表皮提供韧性并保护其免受水分损失。在陆生脊椎动物中，角蛋白基因形成了两个主要的簇，簇1和簇2，每个簇都由I型和II型角蛋白基因主导。相比之下，硬骨鱼中没有观察到这样的集群。尽管角蛋白的多样性被认为对陆地适应做出了重大贡献，但其进化过程尚未被阐明。在这里，我们对广泛的脊椎动物的角蛋白基因进行了全面的基因组调查。结果，我们发现古老的鱼类谱系，如象鲨、芦荟、斑点叉尾和腔棘鱼，都有两个角蛋白基因簇。我们还发现了角蛋白基因的扩展，在芦荟中形成了一个新的亚簇。系统发育分析表明，所有脊椎动物共有两对krt18/krt8角蛋白基因，这意味着它们编码祖先的I型和II型角蛋白。我们进一步揭示了不同的角蛋白基因亚群，它们在成年两栖动物的表皮中有特异的表达，起源于非陆地祖先中的规范角蛋白基因。分子进化分析表明，在两栖动物的成体表皮亚群以及芦荟的新亚群中，选择性限制被放松。本研究的结果代表了角蛋白通过一系列基因复制的多样化过程，这可能有助于脊椎动物的陆地适应。
Type I and type II keratins are subgroups of intermediate filament proteins that provide toughness to the epidermis and protect it from water loss. In terrestrial vertebrates, the keratin genes form two major clusters, clusters 1 and 2, each of which is dominated by type I and II keratin genes. By contrast, such clusters are not observed in teleost fish. Although the diversification of keratins is believed to have made a substantial contribution to terrestrial adaptation, its evolutionary process has not been clarified. Here, we performed a comprehensive genomic survey of the keratin genes of a broad range of vertebrates. As a result, we found that ancient fish lineages such as elephant shark, reedfish, spotted gar, and coelacanth share both keratin gene clusters. We also discovered an expansion of keratin genes that form a novel subcluster in reedfish. Syntenic and phylogenetic analyses revealed that two pairs of krt18/krt8 keratin genes were shared among all vertebrates, thus implying that they encode ancestral type I and II keratin protein sets. We further revealed that distinct keratin gene subclusters, which show specific expressions in the epidermis of adult amphibians, stemmed from canonical keratin genes in non-terrestrial ancestors. Molecular evolutionary analyses suggested that the selective constraints were relaxed in the adult epidermal subclusters of amphibians as well as the novel subcluster of reedfish. The results of the present study represent the process of diversification of keratins through a series of gene duplications that could have facilitated the terrestrial adaptation of vertebrates.