Li Wenhao, Wang Faxiang, Jiang Shouwen, Pan Binbin, Liu Qi, Xu Qianghua
Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources, Ministry of Education, College of Marine Sciences, Shanghai Ocean University, Shanghai, China.
Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai, China.
Front Cell Dev Biol. 2022 Sep 12;10:987409. doi: 10.3389/fcell.2022.987409. eCollection 2022.
Hadal zones are unique habitats characterized by high hydrostatic pressure (HHP) and scarce food supplies. The ability of eggs of species dwelling in hadal zones to develop into normal embryo under high hydrostatic pressure is an important evolutionary and developmental trait. However, the mechanisms underlying the development of eggs of hadal-dwelling species remain unknown due to the difficulty of sampling ovigerous females. Here, morphological and transcriptome analyses of eggs of the "supergiant" amphipod collected from the New Britain Trench were conducted. The morphology of . eggs, including size, was assessed and the ultrastructure of the eggshell was investigated by scanning electron microscopy. Transcriptome sequencing and molecular adaptive evolution analysis of . eggs showed that, as compared with shallow-water Gammarus species, genes exhibiting accelerated evolution and the positively selected genes were mostly related to pathways associated with "mitosis" and "chitin-based embryonic cuticle biosynthetic process", suggesting that "normal mitosis maintenance" and "cuticle development and protection" are the two main adaptation strategies for survival of eggs in hadal environments. In addition, the concentration of trimethylamine oxide (TMAO), an important osmotic regulator, was significantly higher in the eggs of hadal amphipods as compared to those of shallow-water species, which might promote the eggs' adaptation abilities. Morphological identification, evolutionary analysis, and the trimethylamine oxide concentration of eggs will facilitate a comprehensive overview of the piezophilic adaptation of embryos in hadal environments and provide a strategy to analyze embryogenesis under high hydrostatic pressure.
超深渊带是独特的栖息地，其特征是高静水压力（HHP）和食物供应稀缺。生活在超深渊带的物种的卵在高静水压力下发育成正常胚胎的能力是一项重要的进化和发育特征。然而，由于难以采集抱卵雌体，超深渊带物种卵发育的潜在机制仍然未知。在此，对从新不列颠海沟采集的“超级巨型”端足类动物的卵进行了形态学和转录组分析。评估了卵的形态，包括大小，并通过扫描电子显微镜研究了卵壳的超微结构。对卵的转录组测序和分子适应性进化分析表明，与浅水钩虾物种相比，表现出加速进化的基因和正选择基因大多与“有丝分裂”和“基于几丁质的胚胎角质层生物合成过程”相关的途径有关，这表明“维持正常有丝分裂”和“角质层发育与保护”是超深渊环境中卵生存的两种主要适应策略。此外，重要的渗透调节剂氧化三甲胺（TMAO）的浓度在超深渊端足类动物的卵中明显高于浅水物种的卵，这可能会提高卵的适应能力。卵的形态鉴定、进化分析以及氧化三甲胺浓度将有助于全面了解超深渊环境中胚胎的嗜压适应性，并提供一种分析高静水压力下胚胎发生的策略。
