School of Biological Sciences, University of Queensland, Brisbane, Queensland, Australia.
PLoS One. 2013 Sep 3;8(9):e72797. doi: 10.1371/journal.pone.0072797. eCollection 2013.
Marine invertebrates commonly have a biphasic life cycle in which the metamorphic transition from a pelagic larva to a benthic post-larva is mediated by the nitric oxide signalling pathway. Nitric oxide (NO) is synthesised by nitric oxide synthase (NOS), which is a client protein of the molecular chaperon heat shock protein 90 (HSP90). It is notable, then, that both NO and HSP90 have been implicated in regulating metamorphosis in marine invertebrates as diverse as urochordates, echinoderms, molluscs, annelids, and crustaceans. Specifically, the suppression of NOS activity by the application of either NOS- or HSP90-inhibiting pharmacological agents has been shown consistently to induce the initiation of metamorphosis, leading to the hypothesis that a negative regulatory role of NO is widely conserved in biphasic life cycles. Further, the induction of metamorphosis by heat-shock has been demonstrated for multiple species. Here, we investigate the regulatory role of NO in induction of metamorphosis of the solitary tropical ascidian, Herdmania momus. By coupling pharmacological treatments with analysis of HmNOS and HmHSP90 gene expression, we present compelling evidence of a positive regulatory role for NO in metamorphosis of this species, in contrast to all existing ascidian data that supports the hypothesis of NO as a conserved negative regulator of metamorphosis. The exposure of competent H. momus larvae to a NOS inhibitor or an NO donor results in an up-regulation of NOS and HSP90 genes. Heat shock of competent larvae induces metamorphosis in a temperature dependent manner, up to a thermal tolerance that approaches 35°C. Both larval/post-larval survival and the appearance of abnormal morphologies in H. momus post-larvae reflect the magnitude of up-regulation of the HSP90 gene in response to heat-shock. The demonstrated role of NO as a positive metamorphic regulator in H. momus suggests the existence of inter-specific adaptations of NO regulation in ascidian metamorphosis.
海洋无脊椎动物通常具有双相生活史，其中从浮游幼虫到底栖幼体的变态过渡是由一氧化氮信号通路介导的。一氧化氮（NO）由一氧化氮合酶（NOS）合成，NOS 是分子伴侣热休克蛋白 90（HSP90）的客户蛋白。值得注意的是，NO 和 HSP90 都参与调节海洋无脊椎动物的变态，包括尾索动物、棘皮动物、软体动物、环节动物和甲壳动物。具体而言，NOS 活性的抑制通过应用 NOS 或 HSP90 抑制性药理学剂一直被证明可以诱导变态的开始，导致假设 NO 的负调节作用在双相生活史中广泛保守。此外，热休克已被证明可诱导多种物种的变态。在这里，我们研究了 NO 在热带孤立海鞘 Herdmania momus 变态中的调节作用。通过将药理学处理与 HmNOS 和 HmHSP90 基因表达分析相结合，我们提供了令人信服的证据，证明 NO 在该物种变态中具有正调节作用，与所有现有的海鞘数据相反，这些数据支持 NO 作为保守的变态负调节剂的假设。将有能力的 H. momus 幼虫暴露于 NOS 抑制剂或 NO 供体中会导致 NOS 和 HSP90 基因的上调。有能力的幼虫的热休克以依赖于温度的方式诱导变态，直至接近 35°C 的热耐受性。H. momus 幼体的幼虫/幼体存活率和异常形态的出现反映了 HSP90 基因对热休克的上调幅度。NO 在 H. momus 中作为正性变态调节剂的作用表明，NO 调节在海鞘变态中存在种间适应性。
