Brain-derived neurotrophic factor (BDNF), one of the neurotrophins, and its specific receptor TrkB, are abundantly distributed in the central nervous system (CNS) and have a variety of biological effects, such as neural survival, neurite elongation, neural differentiation, and enhancing synaptic functions. Currently, there are two TrkB subtypes: full-length TrkB (TrkB-FL), which has a tyrosine kinase in the intracellular domain, and TrkB-T1, which is a tyrosine kinase-deficient form. While TrkB-FL is a typical tyrosine kinase receptor, TrkB-T1 is a main form expressed in the CNS of adult mammals, but its function is unknown. In this study, we performed fluorescent staining of the cerebral cortex of adult mice, by using TrkB-T1 antiserum and various antibodies of marker molecules for neurons and glial cells. We found that TrkB-T1 was expressed not only in neurons but also in astrocytes. In contrast, little expression of TrkB-T1 was found in oligodendrocytes and microglia. TrkB-T1 was expressed in almost all of the cells expressing TrkB-FL, indicating the direct interaction between TrkB subtypes. These findings suggest that a part of various functions of BDNF-TrkB signaling might be due to the interaction and cellular localization of TrkB subtypes in the cerebral cortex.

中文翻译：

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成年小鼠大脑皮层中截短 TrkB 的定位及其与全长 TrkB 的共表达

脑源性神经营养因子（BDNF）是神经营养因子之一，其特异性受体TrkB广泛分布于中枢神经系统（CNS）中，具有多种生物学效应，如神经存活、神经突伸长、神经分化、并增强突触功能。目前，有两种 TrkB 亚型：全长 TrkB (TrkB-FL)，其胞内结构域具有酪氨酸激酶；TrkB-T1，其是酪氨酸激酶缺陷形式。TrkB-FL是典型的酪氨酸激酶受体，而TrkB-T1是成年哺乳动物CNS中表达的主要形式，但其功能尚不清楚。在本研究中，我们使用 TrkB-T1 抗血清以及神经元和神经胶质细胞标记分子的各种抗体对成年小鼠的大脑皮层进行荧光染色。我们发现TrkB-T1不仅在神经元中表达，也在星形胶质细胞中表达。相反，在少突胶质细胞和小胶质细胞中几乎没有发现 TrkB-T1 表达。TrkB-T1 在几乎所有表达 TrkB-FL 的细胞中表达，表明 TrkB 亚型之间存在直接相互作用。这些发现表明，BDNF-TrkB 信号传导的各种功能的一部分可能是由于大脑皮层中 TrkB 亚型的相互作用和细胞定位所致。