Hemostasis in vertebrates involves both a cellular and a protein component. Previous studies in jawless vertebrates (cyclostomes) suggest that the protein response, which involves thrombin-catalyzed conversion of a soluble plasma protein, fibrinogen, into a polymeric fibrin clot, is conserved in all vertebrates. However, similar data are lacking for the cellular response, which in gnathostomes is regulated by von Willebrand factor (VWF), a glycoprotein that mediates the adhesion of platelets to the subendothelial matrix of injured blood vessels. To gain evolutionary insights into the cellular phase of coagulation, we asked whether a functional vwf gene is present in the Atlantic hagfish, Myxine glutinosa We found a single vwf transcript that encodes a simpler protein compared with higher vertebrates, the most striking difference being the absence of an A3 domain, which otherwise binds collagen under high-flow conditions. Immunohistochemical analyses of hagfish tissues and blood revealed Vwf expression in endothelial cells and thrombocytes. Electron microscopic studies of hagfish tissues demonstrated the presence of Weibel-Palade bodies in the endothelium. Hagfish Vwf formed high-molecular-weight multimers in hagfish plasma and in stably transfected CHO cells. In functional assays, botrocetin promoted VWF-dependent thrombocyte aggregation. A search for vwf sequences in the genome of sea squirts, the closest invertebrate relatives of hagfish, failed to reveal evidence of an intact vwf gene. Together, our findings suggest that VWF evolved in the ancestral vertebrate following the divergence of the urochordates some 500 million years ago and that it acquired increasing complexity though sequential insertion of functional modules.

中文翻译：

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现存脊椎动物粘液粘菌 vWF 的鉴定：原发性止血的进化保护

脊椎动物的止血涉及细胞成分和蛋白质成分。先前对无颌脊椎动物（圆口动物）的研究表明，蛋白质反应，包括凝血酶催化将可溶性血浆蛋白纤维蛋白原转化为聚合纤维蛋白凝块，在所有脊椎动物中都是保守的。然而，细胞反应缺乏类似的数据，在有颚类动物中，细胞反应受血管性血友病因子 (VWF) 调节，VWF 是一种糖蛋白，可介导血小板与受损血管内皮下基质的粘附。为了获得对凝血细胞阶段的进化见解，我们询问大西洋盲鳗中是否存在功能性 vwf 基因，粘粘菌我们发现了一个单一的 vwf 转录物，与高等脊椎动物相比，它编码的蛋白质更简单，最显着的区别是没有 A3 结构域，否则它会在高流量条件下结合胶原蛋白。盲鳗组织和血液的免疫组织化学分析显示内皮细胞和血小板中 Vwf 表达。盲鳗组织的电子显微镜研究表明内皮中存在 Weibel-Palade 小体。盲鳗 Vwf 在盲鳗血浆和稳定转染的 CHO 细胞中形成高分子量多聚体。在功能测定中，botrocetin 促进了 VWF 依赖性血小板聚集。在海鞘的基因组中搜索 vwf 序列，海鞘是盲鳗的最近的无脊椎动物亲属，但未能揭示完整的 vwf 基因的证据。一起，