中国科学院昆明动物研究所机构知识库

树鼩（Tupaia belangeri）隶属攀鼩目，广泛分布于南亚、东南亚及我国西南地区。其具有体型小、脑-体重比例较高、生殖周期短、饲养成本低等独特优势。基于遗传学的分析表明，与目前广泛使用的模型动物小鼠和大鼠相比，树鼩与灵长类亲缘关系更接近，且被认为是有望替代昂贵的灵长类动物的新型模型实验动物。目前，已经有多种疾病相关的树鼩动物模型被报道，比如乙型肝炎病毒感染，压力与抑郁，情绪相关精神疾病，乳腺癌，血栓疾病和代谢性疾病等。在脑的结构上，相较于大鼠和小鼠，树鼩大脑前额叶皮质发育较好，与灵长类更为相似；在进化上，树鼩的神经系统与灵长类神经系统较为接近。这些特点说明树鼩较为适合作为一种研究脑功能和精神神经疾病的动物模型。脑的发育和衰老涉及到多个表观遗传系统改变，包括DNA甲基化和去甲基化模式。研究表明，5-mC（5-methylcytosine）能被TET（Ten Eleven Translocation）蛋白氧化生成DNA去甲基化中间产物5-hmC（5-hydroxymethylcytosine）。5-hmC在神经元内含量非常丰富则暗示了，在脑的生长发育以及中枢神经系统疾病的发生发展过程中5-hmC可能有着重要的调控作用。在本研究中，我们对幼龄到老年树鼩（出生10天、3月龄、1岁、2岁、4岁和5岁）的五个脑区（额叶皮层、顶叶皮层、颞叶皮层、海马和小脑皮层）中5-hmC水平进行了检测，以观察5-hmC水平在树鼩脑的发育和衰老过程中的动态变化。结合免疫组化染色和Dot Blot检测，结果显示在树鼩出生后至成年的大脑发育过程中，在不同脑区的细胞中5-hmC水平都呈现出逐渐增加；而随着衰老，在老年树鼩的额叶皮层和海马区域中，5-hmC水平又发生一定程度的下降。同时，我们还检测了Tet家族基因在多个年龄树鼩的不同脑区中转录水平的相对变化。结果表明三个Tet基因在不同脑区中随着年龄增加具有不同的表达特点：在前额叶皮层、海马和小脑皮层中，Tet3转录水平变化呈现随脑发育过程增加而随衰老降低的趋势；Tet2/Tet3转录水平在颞叶皮层和三个Tet基因在顶叶皮层中的总体表达模式一定程度上与5-hmC变化是对应关联的。 本研究阐明了5-hmC和Tet家族基因的表达模式在树鼩的大脑发育和老化过程中的动态变化规律，暗示了5-hmC可能是一种潜在的脑发育和衰老的生物学标志物，为相关研究提供了新的见解。这些研究发现也为将来在树鼩模型上进行表观遗传因子在脑发育和衰老过程中的调控功能打下了基础。

The tree shrew (Tupaia belangeri), placed in the order Scandentia, is widely distributing in South Asia, Southeast Asia, and Southwest China, characterized by small size, high brain-to- weight ratio, short reproductive cycle, and economic feeding cost. Comprehensive genetic analyses indicate that tree shrews are genetically closer to primates than widely used model animals such as mice and rats, and thus they are considered to be novel experimental animals that can replace primates as a viable animal model in biomedical research and drug safety testing. At present, many disease model of tree shrew have been reported, such as hepatitis B virus infection, social stress and depression, mood-related mental illness, breast cancer, thrombotic disease as well as metabolic diseases. The tree shrew brain is more similar to that of primates than rats and mice in structure, particularly the morphology of prefrontal cortex and component of the nervous system. These merits suggest that tree shrews are more suitable animals for studying brain function and psychiatric neuropathy. Brain development and aging are associated with alterations in multiple epigenetic systems, including DNA methylation and demethylation patterns. 5-hmC (5-hydroxymethylcytosine) is intermediate product of demethylation process, derived from oxidation of 5-mC (5-methylcytosine) by TET (Ten Eleven Translocation) proteins. Its high level in neurons implies that 5-hmC potentially played a role in neurodevelopment and neurological diseases. To address if postnatal brain development could be attributed to active DNA demethylation, we examined the 5-hmC levels in the prefrontal cortex (PFC), parietal cortex (PC), occipital cortex (OC), hippocampus (HP), and cerebellum (CB) of P10, 3-month, 1-year, 2-year, 4-year, and 5-year-old tree shrew brains using immunohistochemistry and Dot Blot assay. The levels of 5-hmC in tree shrew multiple anatomic structures show a gradual increase throughout postnatal development, whereas, in aged tree shrews, a significant decrease of 5-hmC was found in several brain regions, including prefrontal cortex and hippocampus but not in cerebellum. To test if changes in 5-hmC levels were directly associated with levels of Tet mRNA expression in tree shrew brains during postnatal development and aging, we examined their expression patterns. We observed a diversity of expression patterns of Tet genes: in PFC, HP and Cerebellum, the expression of Tet3 increases with development while decreases during aging; interestingly, the mRNA levels of all three Tet genes in the PC, and Tet2/Tet3 in the OC showed significant increases during postnatal development, consistent with 5-hmC change patterns.In summary, we reported the dynamic changes of 5-hmC and expression patterns of Tet genes during tree shrew brain development and aging, which may function as a biomarker and plays a regulatory role in the biological processes of brain development and aging. Our study also has further significance for mechanism research of epigenetic regulation in brain development and aging on disease animal model of tree shrew.