Burke R D
Department of Biology, University of Victoria, British Columbia, Canada.
Int Rev Cytol. 1999;191:257-84. doi: 10.1016/s0074-7696(08)60161-8.
Integrins are a family of molecules that have fundamental roles in cell-cell and cell-matrix adhesion. It is thought that all metazoan cells have one or more integrin receptors on their surface and that these molecules may have been key in the evolution of multicellularity. Knowledge of the structure, function, and distribution of integrin subunits in invertebrate phyla remains incomplete. However, through the recent use of polymerase chain reaction, integrin subunits have been identified in at least five phyla; sponges, cnidarians, nemadodes, arthropods, and echinoderms. The structure of all of the invertebrate subunits is remarkably similar to that of vertebrate integrin subunits. Some experimental data and patterns of expression indicate that invertebrate integrins have a range of functions similar to those of vertebrate integrins. The ligands are not well characterized but at least two laminin-binding receptors have been identified and two other receptors appear to bind using Arg-Gly-Asp motifs. Invertebrate integrins are present during development, in adults, and on a range of cell types including cells with immunological functions such as hemocytes and coelomocytes. Analysis of the invertebrate beta subunits indicates that the invertebrate integrins have diverged independently within each phylum. The two major clades of vertebrate integrins (beta 1, beta 2, beta 7 and beta 3, beta 5, beta 6, beta 8) appear to have radiated since the divergence of the deuterostomes and there are no distinct orthologous subunits in any of the invertebrate phyla. Since fundamental functions of integrins appear to be conserved, studies of invertebrate integrins have the potential of contributing to our understanding of this important group of receptors.
整合素是一类在细胞间和细胞与基质黏附中起基础作用的分子。据认为，所有后生动物细胞表面都有一个或多个整合素受体，并且这些分子可能在多细胞生物的进化过程中起关键作用。关于无脊椎动物门中整合素亚基的结构、功能和分布的知识仍然不完整。然而，通过最近使用聚合酶链反应，已在至少五个门中鉴定出整合素亚基；海绵动物门、刺胞动物门、线虫动物门、节肢动物门和棘皮动物门。所有无脊椎动物亚基的结构与脊椎动物整合素亚基的结构非常相似。一些实验数据和表达模式表明，无脊椎动物整合素具有一系列与脊椎动物整合素相似的功能。其配体尚未得到很好的表征，但至少已鉴定出两种层粘连蛋白结合受体，另外两种受体似乎使用精氨酸 - 甘氨酸 - 天冬氨酸基序进行结合。无脊椎动物整合素在发育过程中、成体中以及一系列细胞类型上都存在，包括具有免疫功能的细胞，如血细胞和体腔细胞。对无脊椎动物β亚基的分析表明，无脊椎动物整合素在每个门内独立分化。脊椎动物整合素的两个主要分支（β1、β2、β7和β3、β5、β6、β8）似乎自后口动物分化以来就已经辐射分化，并且在任何无脊椎动物门中都没有明显的直系同源亚基。由于整合素的基本功能似乎是保守的，对无脊椎动物整合素的研究有可能有助于我们理解这一重要的受体群体。
