Fujimori Kazuhiro, Takauji Rumiko, Tamamaki Nobuaki
Department of Anatomy, Fukui Medical University, Matsuoka, 910-1193 Fukui, Japan.
J Comp Neurol. 2002 Aug 5;449(4):330-42. doi: 10.1002/cne.10286.
Microtubule-associated protein 2 (MAP2) occurs in developing mammalian neuronal tissue as both high- and low-molecular-weight forms with temporally regulated expression. We studied the MAP2 expression in the developing rat telencephalon with monoclonal antibodies that recognized both the high- and low-molecular-weight forms of MAP2 variants or that specifically recognized high-molecular-weight forms of MAP2 variants. Differences in the staining patterns of these antibodies reflected differences in the distribution of the high- and low-molecular-weight MAP2s. The immunoreactive sites of high- and low-molecular-weight MAP2 had a more widespread distribution in the embryonic telencephalon than those of high-molecular-weight MAP2. Many bipolar cells in the ganglionic eminence (GE) and in the intermediate zone (IZ) of the neocortex showed low-molecular-weight MAP2 immunoreactivity, but they showed weak or no high-molecular-weight MAP2 immunoreactivity. Expression of mRNA containing exons common to high- and low-molecular-weight MAP2 was detected in the tangentially ellipsoidal cells in the IZ, but expression of mRNA containing an exon specific to high-molecular-weight MAP2 was not detected in these cells by in situ hybridization. We interpreted these observations as indicating that the bipolar cells contained MAP2c preferentially, but contained MAP2a and MAP2b (MAP2a/b) at a very low or negligible level. The cells that expressed MAP2c preferentially among the MAP2 splicing variants composed 50% of the preplate cells, most of the MAP2-positive cells in the hippocampus and the corpus callosum. Double labeling by DiI staining and Dlx2 immunohistochemistry, or by Dlx2 and MAP2 immunohistochemistry, revealed that most of the Dlx2-positive cells in the IZ expressed MAP2c preferentially at embryonic day 16. Another double-labeling study revealed that most GAD-positive cells in the preplate were MAP2a/b positive, whereas most GAD-positive cells in the IZ expressed MAP2c preferentially, with only a negligible level of MAP2a/b immunoreactivity. We conclude that MAP2 immunoreactivity in the IZ was localized in the tangentially migrating neurons. The tangentially migrating neurons seemed to acquire MAP2a/b immunoreactivity as they entered the preplate or cortical plate and developed into mature neurons. Radially migrating neurons in the IZ were MAP2 negative. After entering to the preplate or the cortical plate, they became MAP2a/b positive as they developed into mature neurons.
微管相关蛋白2（MAP2）以高分子量和低分子量两种形式出现在发育中的哺乳动物神经组织中，其表达具有时间调控性。我们用单克隆抗体研究了发育中的大鼠端脑内MAP2的表达情况，这些抗体既能识别MAP2变体的高分子量和低分子量形式，也能特异性识别MAP2变体的高分子量形式。这些抗体染色模式的差异反映了高分子量和低分子量MAP2分布的不同。高分子量和低分子量MAP2的免疫反应位点在胚胎端脑中的分布比高分子量MAP2更为广泛。神经节隆起（GE）和新皮质中间区（IZ）的许多双极细胞显示出低分子量MAP2免疫反应性，但它们显示出弱的或无高分子量MAP2免疫反应性。通过原位杂交在IZ的切向椭圆形细胞中检测到含有高分子量和低分子量MAP2共同外显子的mRNA表达，但在这些细胞中未检测到含有高分子量MAP2特异性外显子的mRNA表达。我们将这些观察结果解释为表明双极细胞优先含有MAP2c，但含有极低水平或可忽略不计水平的MAP2a和MAP2b（MAP2a/b）。在MAP2剪接变体中优先表达MAP2c的细胞占前板细胞的50%，海马体和胼胝体中大多数MAP2阳性细胞也如此。通过DiI染色和Dlx2免疫组织化学双标记，或通过Dlx2和MAP2免疫组织化学双标记发现，在胚胎第16天，IZ中大多数Dlx2阳性细胞优先表达MAP2c。另一项双标记研究表明，前板中大多数GAD阳性细胞为MAP2a/b阳性，而IZ中大多数GAD阳性细胞优先表达MAP2c，只有可忽略不计水平的MAP2a/b免疫反应性。我们得出结论，IZ中的MAP2免疫反应性定位于切向迁移的神经元中。切向迁移的神经元在进入前板或皮质板并发育为成熟神经元时似乎获得了MAP2a/b免疫反应性。IZ中的径向迁移神经元MAP2呈阴性。进入前板或皮质板后，它们在发育为成熟神经元时变为MAP2a/b阳性。
