Obinata Takashi, Amemiya Shonan, Takai Ryosuke, Ichikawa Muneyoshi, Toyoshima Yoko Y, Sato Naruki
1 Department of Biology, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 262-8522, Japan.
Zoolog Sci. 2014 Mar;31(3):122-8. doi: 10.2108/zsj.31.122.
Troponin, a Ca(2+)-dependent regulator of striated muscle contraction, has been characterized in vertebrates, protochordates (amphioxus and ascidian), and many invertebrate animals that are categorized in protostomes, but it has not been detected in echinoderms, such as sea urchin and sea cucumber, members of subphylum Eleutherozoa. In this study, we examined the muscle of a species of isocrinid sea lilies, a member of subphylum Pelmatozoa, that constitute the most basal group of extant echinoderms to clarify whether troponin is lacking from the early evolution of echinoderms. Native thin filaments were released from the muscle homogenates in a relaxing buffer containing ATP and EGTA, a Ca(2+)-chelator, and were collected by ultra-centrifugation. Actin and tropomyosin, but not a troponin-like protein, were detected in the filament preparation. The filaments increased Mg(2+)-ATPase activity of rabbit skeletal muscle myosin irrespective of the presence or absence of Ca(2+). The results indicate that Ca(2+)-sensitive factor, troponin, is lacking in the thin filaments of sea lily muscle as in those of the other echinoderms, sea urchin and sea cucumber. On the other hand, a paramyosin-like protein that is absent from chordates was detected in sea lily muscle as in the muscles of the other echinoderms and invertebrate animals of protostomes.
肌钙蛋白是一种依赖钙离子调节横纹肌收缩的蛋白，已在脊椎动物、原索动物（文昌鱼和海鞘）以及许多被归类为原口动物的无脊椎动物中得到表征，但在棘皮动物（如紫海胆和海参等游走亚门成员）中尚未检测到。在本研究中，我们检测了海百合纲一种海百合的肌肉，海百合纲属于海扁果亚门，是现存棘皮动物中最基础的类群，以阐明棘皮动物早期进化过程中是否缺乏肌钙蛋白。在含有ATP和钙离子螯合剂EGTA的松弛缓冲液中，从肌肉匀浆中释放出天然细肌丝，并用超速离心法收集。在细肌丝制剂中检测到了肌动蛋白和原肌球蛋白，但未检测到类肌钙蛋白。无论有无钙离子，这些细肌丝都能提高兔骨骼肌肌球蛋白的镁离子ATP酶活性。结果表明，海百合肌肉的细肌丝中缺乏钙离子敏感因子肌钙蛋白，就像其他棘皮动物（紫海胆和海参）的细肌丝一样。另一方面，在海百合肌肉中检测到了一种脊索动物所没有的类副肌球蛋白，其他棘皮动物和原口动物的无脊椎动物肌肉中也有这种蛋白。
