The integrity and organization of animal tissues depend upon specialized protein complexes that mediate adhesion between cells with each other (cadherin-based adherens junctions), and with the extracellular matrix (integrin-based focal adhesions). Reconstructing how and when these cell junctions evolved is central to understanding early tissue evolution in animals. We examined focal adhesion protein homologs in tissues of the freshwater sponge, Ephydatia muelleri (phylum Porifera; class Demospongiae). Our principal findings are that (1) sponge focal adhesion homologs (integrin, talin, focal adhesion kinase, etc.) co-precipitate as a complex, separate from adherens junction proteins; (2) that actin-based structures resembling focal adhesions form at the cell-substrate interface, and their abundance is dynamically regulated in response to fluid shear; (3) focal adhesion proteins localize to both cell-cell and cell-extracellular matrix adhesions, and; (4) the adherens junction protein β-catenin is co-distributed with focal adhesion proteins at cell-cell junctions everywhere except the choanoderm, and at novel junctions between cells with spicules, and between cells with environmental bacteria. These results clarify the diversity, distribution and molecular composition of cell junctions in tissues of E. muelleri, but raise new questions about their functional properties and ancestry.

中文翻译：

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海绵组织（Porifera）中具有独特分子组成的多样细胞连接。

动物组织的完整性和组织取决于专门的蛋白质复合物，它们介导细胞之间（基于钙粘着蛋白的粘附连接）以及细胞外基质（基于整合素的粘着粘附）之间的粘附。重建这些细胞接头如何以​​及何时进化对理解动物早期组织进化至关重要。我们检查了淡水海绵，Ephydatia muelleri（门孔虫； Demospongiae类）组织中的粘着斑蛋白同源物。我们的主要发现是：（1）海绵粘着斑同源物（整联蛋白，塔林蛋白，粘着斑激酶等）以复合物的形式共沉淀，与粘附的连接蛋白分开；（2）在细胞-底物界面形成类似于粘着斑的基于肌动蛋白的结构，并根据流体剪切动态调节其丰度；（3）粘着斑蛋白既定位于细胞-细胞又粘附于细胞-细胞外基质，并且；（4）粘附连接蛋白β-catenin与粘着斑蛋白共分布在除软骨组织以外的所有细胞-细胞连接处，以及针状细胞之间和环境细菌细胞之间的新型连接处。这些结果阐明了穆勒埃里希氏菌组织中细胞接头的多样性，分布和分子组成，但提出了有关其功能特性和血统的新问题。（4）粘附连接蛋白β-catenin与粘着斑蛋白共分布在除软骨层以外的所有细胞-细胞连接处，以及针状细胞之间和环境细菌细胞之间的新连接处。这些结果阐明了穆勒埃里希氏菌组织中细胞接头的多样性，分布和分子组成，但提出了有关其功能特性和血统的新问题。（4）粘附连接蛋白β-catenin与粘着斑蛋白共分布在除软骨组织以外的所有细胞-细胞连接处，以及针状细胞之间和环境细菌细胞之间的新型连接处。这些结果阐明了穆勒埃里希氏菌组织中细胞接头的多样性，分布和分子组成，但提出了有关其功能特性和血统的新问题。