AIMS@JCU, James Cook University, Townsville, Queensland, Australia.
PLoS One. 2012;7(7):e39099. doi: 10.1371/journal.pone.0039099. Epub 2012 Jul 6.
Corals, like many other marine invertebrates, lack a mature allorecognition system in early life history stages. Indeed, in early ontogeny, when corals acquire and establish associations with various surface microbiota and dinoflagellate endosymbionts, they do not efficiently distinguish between closely and distantly related individuals from the same population. However, very little is known about the molecular components that underpin allorecognition and immunity responses or how they change through early ontogeny in corals.
METHODOLOGY/PRINCIPAL FINDINGS: Patterns in the expression of four putative immune response genes (apextrin, complement C3, and two CELIII type lectin genes) were examined in juvenile colonies of Acropora millepora throughout a six-month post-settlement period using quantitative real-time PCR (qPCR). Expression of a CELIII type lectin gene peaked in the fourth month for most of the coral juveniles sampled and was significantly higher at this time than at any other sampling time during the six months following settlement. The timing of this increase in expression levels of putative immune response genes may be linked to allorecognition maturation which occurs around this time in A. millepora. Alternatively, the increase may represent a response to immune challenges, such as would be involved in the recognition of symbionts (such as Symbiodinium spp. or bacteria) during winnowing processes as symbioses are fine-tuned.
CONCLUSIONS/SIGNIFICANCE: Our data, although preliminary, are consistent with the hypothesis that lectins may play an important role in the maturation of allorecognition responses in corals. The co-expression of lectins with apextrin during development of coral juveniles also raises the possibility that these proteins, which are components of innate immunity in other invertebrates, may influence the innate immune systems of corals through a common pathway or system. However, further studies investigating the expression of these genes in alloimmune-challenged corals are needed to further clarify emerging evidence of a complex innate immunity system in corals.
珊瑚与许多其他海洋无脊椎动物一样，在早期生活史阶段缺乏成熟的同种异体识别系统。事实上，在早期的个体发育过程中，珊瑚获得并与各种表面微生物群和虫黄藻共生体建立联系时，它们不能有效地将来自同一群体的密切和远缘个体区分开来。然而，对于支持同种异体识别和免疫反应的分子成分，以及它们在珊瑚早期发育过程中如何变化，人们知之甚少。
方法/主要发现：使用定量实时 PCR（qPCR），在六个月的定居后期间，检查了棘冠花属珊瑚（Acropora millepora）幼年群体中四个假定的免疫反应基因（apertin、补体 C3 和两个 CELIII 型凝集素基因）的表达模式。在大多数取样的珊瑚幼体中，一个 CELIII 型凝集素基因的表达在第四个月达到峰值，并且在这个时间点的表达水平显著高于定居后六个月中的任何其他采样时间。这些假定的免疫反应基因表达水平的增加时间可能与同种异体识别成熟有关，这种成熟大约在棘冠花属珊瑚的这个时间发生。或者，这种增加可能代表对免疫挑战的反应，例如在共生体（如 Symbiodinium spp. 或细菌）在精细调整共生关系时识别共生体过程中涉及的反应。
结论/意义：尽管我们的数据是初步的，但与凝集素可能在珊瑚同种异体识别反应成熟中发挥重要作用的假设一致。在珊瑚幼体发育过程中，凝集素与 apextrin 的共表达也提出了一种可能性，即这些在其他无脊椎动物中是先天免疫系统的组成部分的蛋白质，可能通过共同的途径或系统影响珊瑚的先天免疫系统。然而，需要进一步研究这些基因在同种免疫挑战的珊瑚中的表达，以进一步澄清珊瑚中复杂先天免疫系统的出现证据。
