眼外来源的少突胶质细胞参与斑马鱼视网膜髓鞘化以及眼动反应

发布时间：2018-08-24 08:15

【摘要】：绝大多数哺乳动物视网膜内是没有髓鞘的,少突胶质细胞异常地出现在眼中会在神经节细胞层形成白色或灰白色条纹状斑块。视网膜内出现髓鞘可能会导致一些视觉功能障碍,例如人视网膜内有髓鞘视神经纤维可能伴随着近视、弱视,其发生机理尚不清晰。虽然一些低等脊椎动物的视网膜内有髓鞘生成,但是视网膜内髓鞘形成的时空动态、少突胶质细胞的来源、髓鞘形成过程中少突胶质细胞的行为以及少突胶质细胞的功能并没有得到清晰地阐述。因此,我们着眼于上述几个方面,对斑马鱼视网膜内髓鞘展开研究。这将为深入了解视网膜内髓鞘的形成提供详细的信息。由于以往缺乏少突胶质细胞特异性标记的转基因动物品系,人们对于髓鞘的研究仅仅局限于通过免疫组化鉴定不同发育阶段的少突胶质细胞以及用电镜观察视网膜内髓鞘形成情况。斑马鱼视网膜内存在少突胶质细胞和髓鞘,并且具有多个标记髓鞘的转基因品系,使其成为研究视网膜内髓鞘发育的一个很好的脊椎动物模型。利用olig2转基因斑马鱼,我们可以实时地观察髓鞘形成的时空动态。我们发现在斑马鱼出生后的第28天,其视网膜内开始形成髓鞘。随着发育斑马鱼视网膜内的少突胶质细胞、神经节细胞的数目不断增加；少突胶质细胞的密度以及髓鞘碱性蛋白(MBP)的表达随发育不断增加,到出生后第3个月维持稳定；神经节细胞和少突胶质细胞数目的比例不断减少,到出生后第3个月维持稳定。关于视网膜内少突胶质细胞的来源问题,通过向鸡的第三脑室注射DiI染料,Ono等人发现视网膜内存在DiI阳性的少突胶质细胞,这提示了少突胶质细胞可能来自于眼球外部。然而,前人的实验并不能证明视网膜内的髓鞘是否全部来自于眼球外部。我们利用眼球翻转和眼球移植实验,直接证明了斑马鱼视网膜内的少突胶质细胞完全来自于眼球外部而非来自于视网膜内自身的干细胞。利用视神经移植,我们可以观察视网膜内单个少突胶质细胞的形态。我们发现不同年龄的少突胶质细胞表现出不同的行为：年轻的少突胶质细胞形成长度较长数目较少的结间体(internodes);成年的少突胶质细胞形成长度较短数目较多的结间体。年龄相关的少突胶质细胞行为学的改变依赖于少突胶质细胞的内在特征而非外在环境。尽管不同年龄的少突胶质细胞行为存在差异,他们包裹髓鞘的能力并没有明显改变。尽管有髓鞘包裹的轴突的直径随年龄的增长而增加,未髓鞘化的轴突的直径却和年龄无显著相关。与其他中枢神经系统不同,斑马鱼视网膜内的髓鞘呈松散的单圈包裹。轴突内径与轴突外径(轴突内径与髓鞘厚度之和)的比值维持在0.6-0.7。斑马鱼视网膜内髓鞘包裹的模式可能对维持视网膜光学透明性以及促进神经冲动地传导是十分重要的。利用斑马鱼眼动行为学实验以及溶血卵磷脂诱导的视网膜内脱髓鞘模型,我们发现斑马鱼视网膜内髓鞘对于斑马鱼眼动反应是有影响的。我们的研究结果表明,斑马鱼视网膜内的髓鞘形成起始于胚胎受精后28天；视网膜内所有的少突胶质细胞来源于眼球外部；不同的少突胶质细胞具有不同的行为,而这是由细胞的内在因素决定的；斑马鱼视网膜内髓鞘是有功能的。综上所述,本研究为了解视网膜内髓鞘以及其生理特性提供了更多的细节。
[Abstract]:In most mammals, there is no myelin sheath in the retina. The abnormal appearance of oligodendrocyte in the eye can form white or Gray Striped plaques in the ganglion cell layer. The presence of myelin sheath in the retina may lead to some visual impairment, such as myopia and amblyopia in the retina. Although myelination occurs in the retina of some lower vertebrates, the temporal and spatial dynamics of myelination, the origin of oligodendrocytes, the behavior of oligodendrocytes during myelination and the function of oligodendrocytes have not been clearly explained. This will provide detailed information on the formation of intraretinal myelin sheath in zebrafish. Due to the lack of oligodendrocyte-specific markers in transgenic animal strains, the study of myelin sheath is limited to the identification of different developmental stages by immunohistochemistry. The presence of oligodendrocytes and myelin sheaths in the retina of zebrafish and the presence of multiple transgenic strains of myelin markers make it a good vertebrate model for studying the development of intraretinal myelin sheaths. We found that myelin began to form in the retina of zebrafish on the 28th day after birth. With the development of oligodendrocytes in the retina of zebrafish, the number of ganglion cells increased; the density of oligodendrocytes and the expression of myelin basic protein (MBP) increased with development. The proportion of ganglion cells and oligodendrocytes decreased and remained stable until the third month after birth. With regard to the origin of oligodendrocytes in the retina, DiI dye was injected into the third ventricle of the chicken, Ono et al. found that there were DiI positive oligodendrocytes in the retina. It is suggested that oligodendrocytes may originate from the outside of the eyeball. However, previous studies do not prove whether all myelin sheaths in the retina originate from the outside of the eyeball. Intramembranous stem cells. Using optic nerve transplantation, we can observe the morphology of individual oligodendrocytes in the retina. We found that oligodendrocytes of different ages behave differently: young oligodendrocytes form longer internodes; adult oligodendrocytes form smaller internodes. Age-related changes in oligodendrocyte behavior depend on the intrinsic characteristics of oligodendrocyte rather than on the external environment. Despite differences in oligodendrocyte behavior at different ages, their ability to encapsulate myelin sheaths has not changed significantly. Although the diameter of myelin-encapsulated axons varies with age Unlike other central nervous systems, the myelin sheath in the retina of zebrafish is loosely wrapped in a single loop. The ratio of the inner diameter of the axon to the outer diameter of the axon (the sum of the inner diameter of the axon and the thickness of the myelin sheath) remains between 0.6 and 0.7. Formula 1 may be important for maintaining optical transparency of the retina and facilitating nerve impulsive conduction. Using zebrafish eye behavior experiments and hemolytic lecithin-induced intraretinal demyelination model, we found that intraretinal myelin sheath of zebrafish has an effect on zebrafish eye movement. Myelin formation in the retina of zebrafish begins 28 days after fertilization; all oligodendrocytes in the retina originate from the outside of the eyeball; different oligodendrocytes behave differently, which is determined by the intrinsic factors of the cells; and the myelin sheath in the retina of zebrafish is functional. The inner myelin sheath and its physiological characteristics provide more details.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：Q436

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