Shimizu Hiroshi, Fujisawa Toshitaka
Department of Developmental Genetics, National Institute of Genetics, Mishima, Japan.
Genesis. 2003 Aug;36(4):182-6. doi: 10.1002/gene.10213.
The heart is assumed to have evolved as the organ for pumping blood. Here we report a pumping phenomenon in Hydra, a member of the phylum Cnidaria. We find that the peduncle, lower quarter of the body column, stores most of the gastrovascular fluid when the animal is an elongate form. Upon contraction of the polyp, the peduncle contracts and transfers the fluid into the rest of the cavity. We also find that Hydra RFamide III, a homolog of cardioexcitatory RFamide neuropeptides in higher organisms, elevates this transfer activity. Further, CnNk-2, a homolog of a cardiomuscular tissue marker Nkx-2.5, is expressed in the endodermal tissue of the peduncle. These observations indicate that the transfer of fluid by the peduncle has a similar neurological and genetic basis to the pumping of blood by the heart, suggesting that the Hydra peduncle and the heart of higher organisms share a common ancestral origin.
心脏被认为是作为泵血器官进化而来的。在此，我们报道了刺胞动物门成员水螅中的一种泵吸现象。我们发现，当水螅呈细长形态时，其身体柱体的下半部分即柄部储存了大部分消化循环液。当水螅收缩时，柄部收缩并将液体转移到腔体的其余部分。我们还发现，水螅RFamide III，一种高等生物中具有心脏兴奋作用的RFamide神经肽的同源物，可提高这种转移活性。此外，CnNk - 2，一种心肌组织标志物Nkx - 2.5的同源物，在柄部的内胚层组织中表达。这些观察结果表明，柄部的液体转移与心脏泵血具有相似的神经学和遗传学基础，这表明水螅柄部与高等生物的心脏有着共同的祖先起源。
