Aouacheria Abdel, Geourjon Christophe, Aghajari Nushin, Navratil Vincent, Deléage Gilbert, Lethias Claire, Exposito Jean-Yves
Laboratoire de Biométrie et Biologie Evolutive, UMR CNRS 5558, Université Claude Bernard Lyon 1, Villeurbanne, France.
Mol Biol Evol. 2006 Dec;23(12):2288-302. doi: 10.1093/molbev/msl100. Epub 2006 Aug 31.
Collagens are thought to represent one of the most important molecular innovations in the metazoan line. Basement membrane type IV collagen is present in all Eumetazoa and was found in Homoscleromorpha, a sponge group with a well-organized epithelium, which may represent the first stage of tissue differentiation during animal evolution. In contrast, spongin seems to be a demosponge-specific collagenous protein, which can totally substitute an inorganic skeleton, such as in the well-known bath sponge. In the freshwater sponge Ephydatia mülleri, we previously characterized a family of short-chain collagens that are likely to be main components of spongins. Using a combination of sequence- and structure-based methods, we present evidence of remote homology between the carboxyl-terminal noncollagenous NC1 domain of spongin short-chain collagens and type IV collagen. Unexpectedly, spongin short-chain collagen-related proteins were retrieved in nonsponge animals, suggesting that a family related to spongin constitutes an evolutionary sister to the type IV collagen family. Formation of the ancestral NC1 domain and divergence of the spongin short-chain collagen-related and type IV collagen families may have occurred before the parazoan-eumetazoan split, the earliest divergence among extant animal phyla. Molecular phylogenetics based on NC1 domain sequences suggest distinct evolutionary histories for spongin short-chain collagen-related and type IV collagen families that include spongin short-chain collagen-related gene loss in the ancestors of Ecdyzosoa and of vertebrates. The fact that a majority of invertebrates encodes spongin short-chain collagen-related proteins raises the important question to the possible function of its members. Considering the importance of collagens for animal structure and substratum attachment, both families may have played crucial roles in animal diversification.
胶原蛋白被认为是后生动物谱系中最重要的分子创新之一。基底膜IV型胶原蛋白存在于所有真后生动物中，并且在同型硬海绵纲中被发现，同型硬海绵纲是一类具有组织良好上皮的海绵群体，这可能代表了动物进化过程中组织分化的第一阶段。相比之下，海绵硬蛋白似乎是一种特定于寻常海绵纲的胶原质蛋白，它可以完全替代无机骨架，比如在著名的沐浴海绵中。在淡水海绵穆氏艾氏海绵中，我们之前鉴定了一个短链胶原蛋白家族，它们可能是海绵硬蛋白的主要成分。通过结合基于序列和结构的方法，我们提供了证据，证明海绵硬蛋白短链胶原蛋白的羧基末端非胶原NC1结构域与IV型胶原蛋白之间存在远缘同源性。出乎意料的是，在非海绵动物中检索到了与海绵硬蛋白短链胶原蛋白相关的蛋白质，这表明与海绵硬蛋白相关的一个家族构成了IV型胶原蛋白家族的进化姐妹。祖先NC1结构域的形成以及海绵硬蛋白短链胶原蛋白相关家族和IV型胶原蛋白家族的分化可能发生在侧生动物 - 真后生动物分化之前，这是现存动物门中最早的分化。基于NC1结构域序列的分子系统发育学表明，海绵硬蛋白短链胶原蛋白相关家族和IV型胶原蛋白家族有着不同的进化历史，其中包括蜕皮动物和脊椎动物祖先中海绵硬蛋白短链胶原蛋白相关基因的丢失。大多数无脊椎动物编码海绵硬蛋白短链胶原蛋白相关蛋白质这一事实，引发了关于其成员可能功能的重要问题。考虑到胶原蛋白对动物结构和基质附着的重要性，这两个家族可能在动物多样化过程中都发挥了关键作用。
