Attenborough Rosalind M F, Hayward David C, Wiedemann Ursula, Forêt Sylvain, Miller David J, Ball Eldon E
Division of Ecology and Evolution, Research School of Biology, Australian National University, Bldg 46, Canberra, ACT 0200, Australia.
Division of Ecology and Evolution, Research School of Biology, Australian National University, Bldg 46, Canberra, ACT 0200, Australia; ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia.
Dev Biol. 2019 Feb 1;446(1):56-67. doi: 10.1016/j.ydbio.2018.11.022. Epub 2018 Dec 3.
Neuropeptides play critical roles in cnidarian development. However, although they are known to play key roles in settlement and metamorphosis, their temporal and spatial developmental expression has not previously been characterized in any coral. We here describe Acropora millepora LWamide and RFamide and their developmental expression from the time of their first appearance, using in situ hybridization and FMRFamide immunohistochemistry. AmRFamide transcripts first appear in the ectoderm toward the oral end of the planula larva following blastopore closure. This oral bias becomes less apparent as the planula develops. The cell bodies of AmRFamide-expressing cells are centrally located in the ectoderm, with narrow projections to the mesoglea and to the cell surface. As the planula approaches settlement, AmRFamide expression disappears and is undetectable in the newly settled polyp. Expressing cells then gradually reappear as the polyp develops, becoming particularly abundant on the tentacles. AmLWamide transcripts first appear in ectodermal cells of the developing planula, with minimal expression at its two ends. The cell bodies of expressing cells lie just above the mesoglea, in a position distinct from those of AmRFamide-expressing cells, and have a narrow projection extending across the ectoderm to its surface. AmLWamide-expressing cells persist for most of the planula stage, disappearing shortly before settlement, but later than AmRFamide-expressing cells. As is the case with AmRFamide, expressing cells are absent from the polyp immediately after settlement, reappearing later on its oral side. AmLWamide expression lags that of AmRFamide in both its disappearance and reappearance. Antibodies to FMRFamide stain cells in a pattern similar to that of the transcripts, but also cells in areas where there is no expression revealed by in situ hybridization, most notably at the aboral end of the planula and in the adult polyp. Adult polyps have numerous staining cells on the tentacles and oral discs, as well as an immunoreactive nerve ring around the mouth. There are scattered staining cells in the coenosarc between polyps and staining cells are abundant in the mesenterial filaments. The above results are discussed in the context of our knowledge of the behavior of coral planulae at the time of their settlement and metamorphosis. Corals are facing multiple environmental threats, and these results both highlight the need for, and bring us a step closer to, a mechanistic understanding of a process that is critical to their survival.
神经肽在刺胞动物的发育过程中发挥着关键作用。然而，尽管已知它们在附着和变态过程中起关键作用，但此前尚未对任何珊瑚中它们的时空发育表达进行过表征。我们在此使用原位杂交和FMRF酰胺免疫组织化学方法，描述了多孔鹿角珊瑚LW酰胺和RF酰胺及其从首次出现时起的发育表达情况。AmRF酰胺转录本在原肠胚孔关闭后首先出现在浮浪幼虫口端的外胚层中。随着浮浪幼虫的发育，这种口端偏向变得不那么明显。表达AmRF酰胺的细胞的细胞体位于外胚层的中央，向中胶层和细胞表面有狭窄的突起。当浮浪幼虫接近附着时，AmRF酰胺表达消失，在新附着的珊瑚虫中无法检测到。然后，随着珊瑚虫的发育，表达细胞逐渐重新出现，在触手处特别丰富。AmLW酰胺转录本首先出现在发育中的浮浪幼虫的外胚层细胞中，在其两端表达最少。表达细胞的细胞体位于中胶层上方，与表达AmRF酰胺的细胞位置不同，并且有一个狭窄的突起穿过外胚层延伸到其表面。表达AmLW酰胺的细胞在浮浪幼虫阶段的大部分时间里持续存在，在附着前不久消失，但比表达AmRF酰胺的细胞消失得晚。与AmRF酰胺的情况一样，附着后珊瑚虫中立即没有表达细胞，后来在其口侧重新出现。AmLW酰胺的表达在消失和重新出现方面都滞后于AmRF酰胺。针对FMRF酰胺的抗体以与转录本相似的模式对细胞进行染色，但也对原位杂交未显示表达的区域中的细胞进行染色，最明显的是在浮浪幼虫的反口端和成年珊瑚虫中。成年珊瑚虫在触手和口盘上有许多染色细胞，以及围绕口部的免疫反应性神经环。在珊瑚虫之间的共肉中有分散的染色细胞，并且在肠系膜丝中有丰富的染色细胞。上述结果在我们对珊瑚浮浪幼虫附着和变态时行为的了解的背景下进行了讨论。珊瑚正面临多种环境威胁，这些结果既突出了对这一对它们的生存至关重要的过程进行机制理解的必要性，也使我们朝着这一目标又迈进了一步。
