Reef Ruth, Dunn Simon, Levy Oren, Dove Sophie, Shemesh Eli, Brickner Itzchak, Leggat William, Hoegh-Guldberg Ove
Centre for Marine Studies and the ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, QLD 4072 Australia.
J Exp Biol. 2009 Sep 1;212(17):2760-6. doi: 10.1242/jeb.031286.
The larvae of most coral species spend some time in the plankton, floating just below the surface and hence exposed to high levels of ultraviolet radiation (UVR). The high levels of UVR are potentially stressful and damaging to DNA and other cellular components, such as proteins, reducing survivorship. Consequently, mechanisms to either shade (prevent) or repair damage potentially play an important role. In this study, the role of photoreactivation in the survival of coral planulae was examined. Photoreactivation is a light-stimulated response to UV-damaged DNA in which photolyase proteins repair damaged DNA. Photoreactivation rates, as well as the localization of photolyase, were explored in planulae under conditions where photoreactivation was or was not inhibited. The results indicate that photoreactivation is the main DNA repair pathway in coral planulae, repairing UV-induced DNA damage swiftly (K=1.75 h(-1) and a half-life of repair of 23 min), with no evidence of any light-independent DNA repair mechanisms, such as nucleotide excision repair (NER), at work. Photolyase mRNA was localized to both the ectoderm and endoderm of the larvae. The amount of cell death in the coral planulae increased significantly when photoreactivation was inhibited, by blocking photoreactivating light. We found that photoreactivation, along with additional UV shielding in the form of five mycosporine-like amino acids, are sufficient for survival in surface tropical waters and that planulae do not accumulate DNA damage despite being exposed to high UVR.
大多数珊瑚物种的幼虫会在浮游生物中度过一段时间，漂浮在水面以下，因此会受到高水平的紫外线辐射（UVR）。高水平的紫外线辐射可能会给DNA和其他细胞成分（如蛋白质）带来压力并造成损害，从而降低存活率。因此，遮挡（预防）或修复损伤的机制可能起着重要作用。在本研究中，我们研究了光复活作用在珊瑚浮浪幼虫存活中的作用。光复活作用是一种对紫外线损伤的DNA的光刺激反应，其中光解酶蛋白修复受损的DNA。我们在光复活作用被抑制或未被抑制的条件下，对浮浪幼虫的光复活率以及光解酶的定位进行了研究。结果表明，光复活作用是珊瑚浮浪幼虫主要的DNA修复途径，能迅速修复紫外线诱导的DNA损伤（K = 1.75 h⁻¹，修复半衰期为23分钟），没有证据表明存在任何不依赖光的DNA修复机制，如核苷酸切除修复（NER）在起作用。光解酶mRNA定位于幼虫的外胚层和内胚层。当通过阻挡光复活光来抑制光复活作用时，珊瑚浮浪幼虫中的细胞死亡量显著增加。我们发现，光复活作用以及以五种类菌孢素氨基酸形式存在的额外紫外线屏蔽，足以使其在热带表层水域中存活，并且浮浪幼虫尽管暴露于高水平的紫外线辐射下，但不会积累DNA损伤。
