Zhao Jing, Iida Atsumi, Ouchi Yasuo, Satoh Shinya, Watanabe Sumiko
Department of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Mol Vis. 2008 Sep 3;14:1623-30.
Glycoprotein m6a (M6a) is a cell-surface glycoprotein that belongs to the myelin proteolipid protein family. M6a is expressed mainly in the nervous system, and its expression and function in mammalian retina have not been described. Using proteomics analysis of mouse retinal membrane fractions, we identified M6a as a retinal membrane protein that is strongly expressed at embryonic stages. Our aim was to reveal the function of M6a in development of mouse retina in this work.
Detailed expression pattern of M6a was examined by immunostaining using frozen sections of mouse retina obtained at various developmental stages. For functional analysis of M6a in mouse retinal development, we performed retorovirus-mediated overexpression of M6a in mouse retinal explant culture. Then, cell differentiation, proliferation and structural maturation of the cells were examined.
M6a transcripts were strongly expressed in embryonic retina. After completion of retinal differentiation, the level of expression decreased as mouse development progressed. Immunohistochemistry showed that in the immature mouse retina, M6a was strongly expressed in the axons of retinal ganglion cells. After birth, M6a expression was confined to the inner plexiform layer, and finally, to the inner and outer plexiform layers of adult mouse retina. M6a expression was completely paralleled by that of the synaptic marker, synaptophysin. Mouse retinal progenitor cells that overexpressed M6a following retrovirus-mediated gene transfer were subjected to in vitro explant or monolayer cultures. The neurite outgrowth of M6a-overexpressing retinal cells was strikingly enhanced, although M6a did not affect differentiation and proliferation.
These results suggest that M6a plays a role in retinal development by regulating neurites, and it may also function to modulate synaptic activities in the adult retina.
糖蛋白m6a（M6a）是一种细胞表面糖蛋白，属于髓磷脂蛋白脂蛋白家族。M6a主要在神经系统中表达，其在哺乳动物视网膜中的表达和功能尚未见报道。通过对小鼠视网膜膜组分进行蛋白质组学分析，我们鉴定出M6a是一种在胚胎阶段强烈表达的视网膜膜蛋白。在本研究中，我们旨在揭示M6a在小鼠视网膜发育中的功能。
使用在不同发育阶段获取的小鼠视网膜冰冻切片进行免疫染色，检查M6a的详细表达模式。为了对M6a在小鼠视网膜发育中的功能进行分析，我们在小鼠视网膜外植体培养中进行了逆转录病毒介导的M6a过表达。然后，检查细胞的分化、增殖和结构成熟情况。
M6a转录本在胚胎视网膜中强烈表达。视网膜分化完成后，随着小鼠发育进程，表达水平下降。免疫组织化学显示，在未成熟的小鼠视网膜中，M6a在视网膜神经节细胞的轴突中强烈表达。出生后，M6a的表达局限于内网状层，最后局限于成年小鼠视网膜的内、外网状层。M6a的表达与突触标记物突触素的表达完全平行。通过逆转录病毒介导的基因转移过表达M6a的小鼠视网膜祖细胞进行体外外植体或单层培养。过表达M6a的视网膜细胞的神经突生长显著增强，尽管M6a不影响分化和增殖。
这些结果表明，M6a通过调节神经突在视网膜发育中发挥作用，并且它也可能在成年视网膜中调节突触活动。
