Common ancestors of starfish (echinoderms) are believed to have planktotrophic larvae, although some species show lecithotrophic larvae, which do not feed before metamorphosis. Furthermore, some lecithotrophic paxillosidan larvae, such as those of Astropecten latespinosus, lack brachiolar arms, the sensory apparatus for the reception of environmental cues in planktotrophic larvae. In this study, we found that the metamorphosis of A. latespinosus was stimulated when larvae were cultured with natural sand from their habitat. We also found that retinoic acid signaling mediated the metamorphosis process upon environmental stimulation, as in planktotrophic larvae. We examined reagent treatments and gene expression analysis by in situ hybridization. Exogenous retinoic acid treatment induced metamorphosis, whereas retinoic acid synthesis inhibitor or antagonist for retinoic acid receptors suppressed metamorphosis. Retinoic acid signalingrelated genes were expressed in juvenile rudiments. In conclusion, we propose that the reception of particular environmental cues is required for the metamorphosis of lecithotrophic larvae. Many marine invertebrates have biphasic life cycles, with planktonic larval and sessile adult phases (1). Because sessile adults have restrictedmotility, the settling of larvae in suitable environments during metamorphosis is of critical importance (2). Therefore, planktonic larvae usually possess sensory apparatuses to respond to specific environmental cues (2).

中文翻译：

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海星 Astropecten latespinosus 卵磷脂幼虫的环境信号和视黄酸信号对变态的调节

海星（棘皮动物）的共同祖先被认为具有浮游营养幼虫，尽管有些物种显示出卵磷脂幼虫，它们在变态前不进食。此外，一些卵磷脂的paxillosidan 幼虫，例如Astropecten latespinosus 的幼虫，缺乏腕臂，即浮游营养幼虫接收环境信号的感觉器官。在这项研究中，我们发现当幼虫用其栖息地的天然沙子培养时，A. latespinosus 的变态受到刺激。我们还发现视黄酸信号在环境刺激下介导了变态过程，如在浮游营养幼虫中。我们通过原位杂交检查了试剂处理和基因表达分析。外源性视黄酸治疗诱导变态，而视黄酸合成抑制剂或视黄酸受体拮抗剂抑制变形。视黄酸信号相关基因在幼鱼中表达。总之，我们认为卵磷脂幼虫的变态需要接受特定的环境线索。许多海洋无脊椎动物具有双相生命周期，具有浮游幼虫和无柄成虫阶段 (1)。由于无柄成虫的运动性受到限制，因此在变态过程中将幼虫安置在合适的环境中至关重要 (2)。因此，浮游幼虫通常拥有对特定环境线索做出反应的感觉器官 (2)。我们提出，卵磷脂幼虫的变态需要接受特定的环境线索。许多海洋无脊椎动物具有双相生命周期，具有浮游幼虫和无柄成虫阶段 (1)。由于无柄成虫的运动能力受到限制，因此在变态过程中将幼虫安置在合适的环境中至关重要 (2)。因此，浮游幼虫通常拥有对特定环境线索做出反应的感觉器官 (2)。我们提出，卵磷脂幼虫的变态需要接受特定的环境线索。许多海洋无脊椎动物具有双相生命周期，具有浮游幼虫和无柄成虫阶段 (1)。由于无柄成虫的运动能力受到限制，因此在变态过程中将幼虫安置在合适的环境中至关重要 (2)。因此，浮游幼虫通常拥有对特定环境线索做出反应的感觉器官 (2)。