Naumann Benjamin, Englert Christoph
Institute of Zoology and Evolutionary Research, Jena, Germany; Leibniz Institute on Aging - Fritz Lipmann Institute, Jena, Germany.
Leibniz Institute on Aging - Fritz Lipmann Institute, Jena, Germany; Institute of Biochemistry and Biophysics, Jena, Germany.
Dev Biol. 2018 Oct 1;442(1):69-79. doi: 10.1016/j.ydbio.2018.07.015. Epub 2018 Jul 21.
Annual killifishes are members of the Aplocheiloidea and live in ephemeral habitats that desiccate regularly during the dry season and refill during the rainy season. Populations of these fishes survive the dry season by producing drought-resistant diapausing eggs that are buried in the substrate. When the pool refills during the rainy season the juveniles hatch, grow rapidly and reproduce until the pool desiccates again during the next dry season. The association with such unpredictable habitats has led to the evolution to a variety of developmental adaptations such as a dispersed/reaggregation phase of the deep blastomeres, three possible diapause stages, extreme tolerance to high salinity and anoxia, an efficient DNA repair system and an extremely short life span. Here, we review the course of the dispersed/reaggregation phase, its evolution and phylogenetic distribution and diversity within the Aplocheiloidea. The phenomenon of blastomere dispersion/reaggregation in these fishes was first described in the 1960s and 70s. Blastomeres of most teleost fishes segregate into three groups that give rise to the enveloping cell layer, the yolk syncytial layer and the deep blastomeres that will form the embryo itself. When epiboly commences, the deep blastomeres form a more or less coherent cell sheet with a so called embryonic shield at it marginal zone marking the area where gastrulation takes place. In annual killifishes, the deep blastomeres segregate when epiboly starts and disperse when epiboly commences. After epiboly has been completed, the deep blastomeres are randomly distributed and migrate all over the enveloping cell layer. After several days they start to reaggregate and form the actual embryo that starts gastrulation. The evolutionary origin and mechanism behind this peculiar developmental pathway have puzzled developmental biologists for almost 50 years. However, several of these annual killifishes (Nothobranchius furzeri, Austrofundulus limnaeus, Austrolebias charrua and Austrolebias bellottii) have become model organisms in studies on developmental physiology, aging and stress tolerance. This has led to the establishment of modern genetic techniques such as transgenesis and cell fate mapping that are now used to tackle questions about the origin and mechanisms behind the dispersal/reaggregation phase.
一年生鳉鱼是鳉鱼总科的成员，生活在短暂的栖息地中，这些栖息地在旱季会定期干涸，在雨季又会重新蓄水。这些鱼类的种群通过产生埋在底物中的抗干旱滞育卵来度过旱季。当雨季水池重新蓄水时，幼鱼孵化出来，迅速生长并繁殖，直到下一个旱季水池再次干涸。与这种不可预测的栖息地的关联导致了各种发育适应性的进化，例如深层卵裂球的分散/重新聚集阶段、三个可能的滞育阶段、对高盐度和缺氧的极端耐受性、高效的DNA修复系统以及极短的寿命。在这里，我们回顾了深层卵裂球分散/重新聚集阶段的过程、其进化以及在鳉鱼总科中的系统发育分布和多样性。这些鱼类中卵裂球分散/重新聚集的现象最早在20世纪60年代和70年代被描述。大多数硬骨鱼类的卵裂球分为三组，分别形成包被细胞层、卵黄多核层和将形成胚胎本身的深层卵裂球。当外包开始时，深层卵裂球形成一个或多或少连贯的细胞片，在其边缘区域有一个所谓的胚胎盾，标志着原肠胚形成发生的区域。在一年生鳉鱼中，深层卵裂球在外包开始时分离，在外包开始时分散。外包完成后，深层卵裂球随机分布并在整个包被细胞层中迁移。几天后，它们开始重新聚集并形成开始原肠胚形成的实际胚胎。这种独特发育途径背后的进化起源和机制已经困扰发育生物学家近50年。然而，这些一年生鳉鱼中的几种（费氏假鳃鳉、湖沼澳鳉、查氏澳鳉和贝氏澳鳉）已经成为发育生理学、衰老和应激耐受性研究中的模式生物。这导致了现代遗传技术的建立，如转基因和细胞命运图谱，现在这些技术被用于解决关于分散/重新聚集阶段的起源和机制的问题。
