McCauley D W
Department of Zoology, University of Texas, Austin, Teaxs 78712, USA.
Dev Biol. 1997 Oct 15;190(2):229-40. doi: 10.1006/dbio.1997.8698.
Hydrozoan larvae normally metamorphose in response to an obligate external environmental cue. Application of certain artificial chemical stimuli will also induce metamorphosis. These chemicals and their inhibitors have been used to define and order some of the signal transduction events involved in this process. Results from this study show that exogenous application of serotonin (5-HT) will induce metamorphosis and that 5-HT immunoreactive cells are present in larvae when they are competent to metamorphose. The 5-HT inhibitors ketanserin, clozapine, and 5,7-DHT prevent metamorphosis from occurring as a response to a natural inducing stimulus. Additionally, 5-HT signaling occurs prior to both an influx of external Ca2+ from seawater and activation of protein kinase C, two other steps in the metamorphic signal transduction pathway. The neuropeptide LWamide, previously shown to induce metamorphosis in a related hydrozoan, Hydractinia echinata, also induced metamorphosis in Phialidium. When larvae were cotreated with LWamide and the 5-HT antagonist ketanserin, settlement occurred but was not followed by polyp morphogenesis. These results are used to present a model for the action of 5-HT during metamorphosis in Phialidium gregarium.
水螅虫幼虫通常会对特定的外部环境线索做出反应而发生变态。施加某些人工化学刺激也会诱导变态。这些化学物质及其抑制剂已被用于确定和梳理这一过程中涉及的一些信号转导事件。这项研究的结果表明，外源性施用血清素（5-羟色胺，5-HT）会诱导变态，并且当幼虫具备变态能力时，幼虫体内存在5-HT免疫反应性细胞。5-HT抑制剂酮色林、氯氮平和5,7-二氢色胺可阻止因自然诱导刺激而发生的变态。此外，5-HT信号传导发生在外部Ca2+从海水中流入以及蛋白激酶C激活之前，这是变态信号转导途径中的另外两个步骤。神经肽LWamide，先前已证明在相关水螅虫——海葵Hydractinia echinata中可诱导变态，在Phialidium中也能诱导变态。当幼虫用LWamide和5-HT拮抗剂酮色林共同处理时，会发生附着，但随后不会发生水螅体形态发生。这些结果被用于提出一个关于5-HT在群居管水母变态过程中作用的模型。
