扬子鳄冬眠生态习性的分子机制

Brumation is the most primitive mechanism adopted by reptiles to adapt extreme cold weather. Thus, reptiles are the best model to determine genetic mechanism underlying the hibernation habit of amniotes. Reptilia consists of birds and non-avian reptiles (snakes, lizards, turtles, and crocodilians), and crocodilians comprise a sister lineage of birds (having the common ancestor). It is worth pointing out that in the reptilians, only the birds are endothermic (warm-blood) animals, like the mammals. Therefore, the crocodilians are the ideal model to understand molecular mechanism of amniote hibernation trait. The Chinese alligator (Alligator sinensis) endemic to China is one of the classical ectothermic (cold-blood) reptiles; when its body temperature drops to near ambient (environmental) temperature, it spontaneously enters dormancy state where it stops eating and slows the respiration and heart rates drastically. The brumating alligators completely depend on the energy stored before brumation and pass the several-month-long dormancy by minimizing the metabolic rate in all organs and performing a perfect coordination among different organs, such as blood, heart, liver, spleen, lung, kidney, intestine, brain, etc. As a result, objectives of this project are to (1) conduct a whole-genome analysis on the transcriptome and methylome sequencing, (2) discover crucial molecular players based on differentially expressed genes and differentially methylated genes, (3) construct intra- and inter-organ gene regulation pathways during dormancy, (4) unravel the genetic basis of brumation behavior in the Chinese alligator, providing a foundation for understanding the evolutionary history of amniote hibernation habit.

爬行动物的冬眠是其应对年度低温期最原始的生态适应性机制，为解析羊膜动物冬眠生态习性分子机制的最为理想的模式类群。爬行动物包括鸟类和非鸟爬行类（蛇、蜥、龟、鳖和鳄），其中鳄类在进化上与鸟类为姐妹支，拥有共同的祖先。有趣的是在整个爬行动物中仅有鸟类与哺乳类一样为恒温动物，所以鳄类又是解析羊膜动物冬眠生态习性分子机制的最佳模式动物群。我国特有的扬子鳄是爬行动物大家族中的代表之一，冬眠期间不进食、不活动，仅藉其在冬眠前期所囤积的能量，通过血液、心、肝、脾、肺、肾、肠和脑等多器官组织的协同作用，维持着年度特殊生命阶段的新陈代谢。鉴此，本项目拟通过对冬眠与非冬眠状态下多器官组织的转录组与甲基化组的差显分析，构建冬眠多器官组织协同代谢的基因调控通路，并藉此揭示扬子鳄冬眠生态习性的分子机制问题，从而为后续深入探索爬行动物群冬眠生态习性的系统进化机制奠定基础

在冬季，面对寒冷及缺乏食物的恶劣生存环境，很多变温动物采用冬眠的方式提高自己的生存率。然而，这一过程的分子机制并未被人们所了解。本项目利用转录组、小RNA组、DNA甲基化组、蛋白质组、+宏基因组等多种组学测序技术进行整合分析，探究扬子鳄冬眠的分子机制。本项目研究表明：（1）扬子鳄冬眠期间，甲状腺激素生物合成、营养吸收与代谢、肌肉收缩、泌尿和免疫功能通路总体上是下调的；脂肪分解通路完全抑制，只有肝脏中的脂肪酸转移运输蛋白基因CPT1A上调表达，提示了扬子鳄与冬眠哺乳动物不同的独特节能策略。（2）冬眠相关基因不只直接受DNA甲基化调控，也受到依赖于DNA甲基化的转录调控网络的控制。（3）我们鉴定并比较了组织特异、物种特异以及保守的季节偏向表达miRNAs，显示了冬眠期间复杂的转录后调控。（4）冬眠期扬子鳄的肠道菌群在组成和结构上与活跃期存在明显差异，此时肠道特异性微生物通过降解利用宿主来源的粘蛋白糖苷维持生命，以适应宿主冬眠禁食期间肠道内食物匮乏的状态。（5）如果未能在适合的环境中冬眠，雌性扬子鳄性腺将受到比雄性更大的影响，卵母细胞成熟相关通路基因显著下调，而这一效应可能开始于冬天里类固醇激素生物合成限制因子STAR基因的下调表达。我们的研究揭示了扬子鳄冬眠生态习性，特别是其冬眠期间的能量利用机制、宿主肠道与微生物的共生关系以及冬眠对扬子鳄次年繁殖的影响三个方面的遗传和表观遗传调控机制。目前，行冬眠习性的外温动物的生存和繁殖受到栖息地破坏和气候变化的影响，我们的研究，将为制定这类物种的保护策略，提供理论基础。