Whitten Miranda M A, Coates Christopher J
Institute of Life Science, Swansea University Medical School, Swansea, UK.
Department of Biosciences, College of Science, Swansea University, Swansea, UK.
Pigment Cell Melanoma Res. 2017 Jul;30(4):386-401. doi: 10.1111/pcmr.12590. Epub 2017 Jun 13.
Melanins (eumelanin and pheomelanin) are synthesized in insects for several purposes including cuticle sclerotization and color patterning, clot formation, organogenesis, and innate immunity. Traditional views of insect immunity detail the storage of pro-phenoloxidases inside specialized blood cells (hemocytes) and their release upon recognition of foreign bodies. Activated phenoloxidases convert monophenols into reactive quinones in a two-step enzymatic reaction, and until recently, the mechanism of tyrosine hydroxylation remained a mystery. Herein, we present our interpretations of these enzyme-substrate complexes. The resultant melanins are deposited onto the surface of microbes to immobilize, agglutinate, and suffocate them. Phenoloxidase activity and melanin production are not limited to the blood (hemolymph) or cuticle, as recent evidence points to more diverse, sophisticated interactions in the gut and with the resident symbionts. This review offers insight into the somewhat neglected areas of insect melanogenesis research, particularly in innate immunity, its role in beneficial insects such as pollinators, the functional versatility of phenoloxidases, and the limitations of common experimental approaches that may impede progress inadvertently.
黑色素（真黑素和褐黑素）在昆虫体内的合成有多种目的，包括表皮硬化和颜色图案形成、凝血、器官发生以及先天免疫。传统的昆虫免疫观点详细描述了前酚氧化酶在特殊血细胞（血细胞）中的储存以及它们在识别异物时的释放。活化的酚氧化酶通过两步酶促反应将单酚转化为活性醌，直到最近，酪氨酸羟化的机制仍然是个谜。在此，我们展示了对这些酶-底物复合物的解读。产生的黑色素沉积在微生物表面，使其固定、凝集并窒息。酚氧化酶活性和黑色素生成不仅限于血液（血淋巴）或表皮，因为最近的证据表明在肠道以及与共生菌之间存在更多样、复杂的相互作用。这篇综述深入探讨了昆虫黑色素生成研究中一些被忽视的领域，特别是在先天免疫方面、其在传粉昆虫等有益昆虫中的作用、酚氧化酶的功能多样性以及可能无意中阻碍研究进展的常见实验方法的局限性。
