Xiao Qing, Xia Jian-Hong, Zhang Xiao-Juan, Li Zhi, Wang Yang, Zhou Li, Gui Jian-Fang
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, University of the Chinese Academy of Sciences, Wuhan 430072, China.
Int J Biol Sci. 2014 Jun 24;10(7):715-32. doi: 10.7150/ijbs.9126. eCollection 2014.
Many organisms in extremely cold environments such as the Antarctic Pole have evolved antifreeze molecules to prevent ice formation. There are four types of antifreeze proteins (AFPs). Type-IV antifreeze proteins (AFP4s) are present also in certain temperate and even tropical fish, which has raised a question as to whether these AFP4s have important functions in addition to antifreeze activity. Here we report the identification and functional analyses of AFP4s in cyprinid fish. Two genes, namely afp4a and afp4b coding for AFP4s, were identified in gibel carp (Carassius auratus gibelio) and zebrafish (Danio rerio). In both species, afp4a and afp4b display a head-to-tail tandem arrangement and share a common 4-exonic gene structure. In zebrafish, both afp4a and afp4b were found to express specifically in the yolk syncytial layer (YSL). Interestingly, afp4a expression continues in YSL and digestive system from early embryos to adults, whereas afp4b expression is restricted to embryogenesis. Importantly, we have shown by using afp4a-specific and afp4b-specifc morpholino knockdown and cell lineage tracing approaches that AFP4a participates in epiboly progression by stabilizing yolk cytoplasmic layer microtubules, and AFP4b is primarily related to convergence movement. Therefore, both AFP4 proteins are essential for gastrulation of zebrafish embryos. Our current results provide first evidence that AFP such as AFP4 has important roles in regulating developmental processes besides its well-known function as antifreeze factors.
许多生活在极端寒冷环境中的生物，如南极的生物，已经进化出抗冻分子以防止结冰。抗冻蛋白（AFP）有四种类型。IV型抗冻蛋白（AFP4s）也存在于某些温带甚至热带鱼类中，这就引发了一个问题，即这些AFP4s除了具有抗冻活性外是否还具有重要功能。在此，我们报告鲤科鱼类中AFP4s的鉴定和功能分析。在银鲫（Carassius auratus gibelio）和斑马鱼（Danio rerio）中鉴定出了两个编码AFP4s的基因，即afp4a和afp4b。在这两个物种中，afp4a和afp4b呈头对头串联排列，并共享一个常见的4外显子基因结构。在斑马鱼中，发现afp4a和afp4b都在卵黄合胞体层（YSL）中特异性表达。有趣的是，从早期胚胎到成体，afp4a在YSL和消化系统中持续表达，而afp4b的表达仅限于胚胎发生阶段。重要的是，我们通过使用afp4a特异性和afp4b特异性吗啉代敲低以及细胞谱系追踪方法表明，AFP4a通过稳定卵黄细胞质层微管参与外包进程，而AFP4b主要与汇聚运动有关。因此，这两种AFP蛋白对于斑马鱼胚胎的原肠胚形成都是必不可少的。我们目前的结果首次证明，像AFP4这样的AFP除了作为抗冻因子的众所周知的功能外，在调节发育过程中也具有重要作用。
