Kusche Kristina, Ruhberg Hilke, Burmester Thorsten
Institute of Zoology, Johannes Gutenberg University Mainz, D-55099 Mainz, Germany.
Proc Natl Acad Sci U S A. 2002 Aug 6;99(16):10545-8. doi: 10.1073/pnas.152241199. Epub 2002 Jul 29.
The velvet worms (Onychophora) are considered living fossils and are closely related to the Euarthropoda. Onychophora possess a tracheal system for respiratory function, but oxygen-transport proteins have been considered unnecessary. Here, we show that the hemolymph of the Epiperipatus sp. (Onychophora: Peripatidae) contains an arthropod-type hemocyanin, demonstrating that such protein exists outside the Euarthropoda. Thus, the evolution of oxygen carriers preceded the divergence of the Onychophora and Euarthropoda and was most likely linked to the evolution of an efficient circulatory system in a low-oxygen environment. The cDNA of the Epiperipatus hemocyanin subunit comprises 2,287 bp and encodes for a protein of 641 aa (73.6 kDa). Phylogenetic analyses of the arthropod hemocyanin sequences show that the Onychophora form a robust sister-group of the Euarthropoda, whereas the monophyly of the Tracheata is not supported.
天鹅绒虫（有爪动物门）被认为是活化石，与真节肢动物关系密切。有爪动物门拥有用于呼吸功能的气管系统，但氧气运输蛋白一直被认为是不必要的。在此，我们表明Epiperipatus sp.（有爪动物门：栉蚕科）的血淋巴含有一种节肢动物类型的血蓝蛋白，证明这种蛋白存在于真节肢动物门之外。因此，氧气载体的进化先于有爪动物门和真节肢动物门的分化，并且很可能与低氧环境中高效循环系统的进化有关。Epiperipatus血蓝蛋白亚基的cDNA包含2287 bp，编码一个641个氨基酸（73.6 kDa）的蛋白质。对节肢动物血蓝蛋白序列的系统发育分析表明，有爪动物门形成了真节肢动物门一个强大的姐妹群，而气管动物门的单系性未得到支持。
