Identification of immature cells in the adult mouse brain

发现在早期发育阶段瞬时表达的分子对于理解成年大脑中的神经元可塑性是重要的。我们专注于神经生长锥之间的胚胎和出生后早期参与神经发生。从新生小鼠脑的神经生长锥富集级分中分离膜蛋白gmp 46（具有46 kDa的分子量的生长锥膜蛋白）。Gmp 46属于免疫球蛋白超家族的成员，并且作为粘附分子起作用。gmp 46 cDNA序列与人柯萨奇病毒和腺病毒受体（CAR）的小鼠同源物相同。Gmp 46/CAR，但不是作为病毒受体，在神经发生事件中发挥生理功能，如神经炎的成束、轴突导向和靶细胞作为粘附分子的识别。通过使用酵母双杂交筛选来鉴定gmp 46/CAR相互作用蛋白（经由C末端的PDZ结构域），我们克隆了PSD 95作为gmp 46/CAR结合伴侣。细胞内蛋白质相互作用似乎调节神经发生的动态运动。Western和北方印迹分析显示，gmp 46/CAR主要在神经系统中表达，在新生小鼠脑中表达最高，出生后迅速下降。免疫组化结果显示，gmp 46/CAR在胚胎和发育中的脑神经管神经上皮中表达丰富。然后，这些区域中的gmp 46/CAR表达下降，并且在出生后21天几乎检测不到。然而，我们发现gmp 46/CAR表达超过1个月，在齿状回和脑室下区，其中一些细胞正在增殖。基于我们的研究结果，我们认为gmp 46/CAR在未成熟细胞中瞬时表达，并且不仅在胚胎而且在成人脑中对神经网络形成起作用。

It is important to find molecules that express transiently in the early developmental stage to understand neuronal plasticity in the adult brain. We focused on a nerve growth cone involved in neurogenesis between the embryo and the early postnatal period. A membrane protein gmp46 (growth cone membrane protein with a molecular mass of 46 kDa) was isolated from the nerve growth cone-enriched fraction of newborn mouse brains. Gmp46 belongs to a member of the immunoglobulin super family and functions as an adhesion molecule. The gmp46 cDNA sequence was identical to the mouse homologue of the human coxsackievirus and adenovirus receptor (CAR). Gmp46/CAR, but not as the virus receptor, functions physiologically in neurogenesis events such as fasciculation of neuritis, axonal guidance, and recognition of the target cell as an adhesion molecule. By using a yeast two-hybrid screen to identify gmp46/CAR interacting protein via the PDZ domain at the C-terminal, we cloned PSD95 as a gmp46/CAR binding partner. The intracellular protein interactions appear to regulate a dynamic motility in neurogenesis. Western and northern blot analyses revealed that gmp46/CAR expressed predominantly in the nervous system and the highest level was observed in the newborn mouse brain followed by rapid decrease after birth. An abundant expression of gmp46/CAR was detected in the neuroepithelium of the neural tube in the embryos and the developing brain by immunohistochemical analysis. Then the expression of gmp46/CAR in these areas decreased and was barely detectable over postnatal 21 days. However, we found gmp46/CAR expression over 1 month in the dentate gyrus and the subventricular zone, where a few cells are proliferating. Based on our findings, we propose that gmp46/CAR transiently expresses in immature cells and plays a role on neuronetwork formations not only in embryo but also in adult brain.