Collet J, Fehrat L, Pollard H, Ribas de Pouplana L, Charton G, Bernard A, Moreau J, Ben-Ari Y, Khrestchatisky M
Departament de Biologia Molecular i Cellular, Centre d'Investigacions i Desenvolupament, CSIC, Barcelona, Spain.
Eur J Neurosci. 1997 Dec;9(12):2723-33. doi: 10.1111/j.1460-9568.1997.tb01701.x.
Tau protein variants are axonal microtubule-associated phosphoproteins whose expression correlates with developmentally regulated neurite outgrowth. A single gene encodes multiple tau transcripts via complex alternative splicing. We studied the expression of the mRNAs encoding N-terminal variants of tau, and we showed distinct alternative splicing of exons 2 and 3 in nervous tissues of the adult rat, including the inner ear, hippocampus, cortex, striatum, brainstem, cerebellum, olfactory bulb and retina. Using the reverse transcriptase-coupled polymerase chain reaction and in situ hybridization, we then focused our developmental study on hippocampal neurons, both in vivo and in vitro, to address the developmental and spatial expression of the alternatively spliced mRNAs encoding N-terminal variants of tau. Tau mRNAs devoid of exons 2 and 3 were present throughout development, although their levels decreased in adults. Those containing exon 2 but not exon 3 were already present in the hippocampus of newborn rats and their levels increased during the first postnatal week, mainly in the pyramidal cell layer. Tau RNAs containing exons 2 and 3 appeared at the end of this period in the pyramidal cell layer and in the dentate granule cells. Exon 2-containing mRNAs seemed to be associated with cells undergoing axonal sprouting, while exon 3-containing RNAs were expressed in mature neurons that had established their connections. The timing and pattern of tau alternative splicing were maintained in cultured hippocampal neurons, suggesting that splicing processes are independent of the organized connectivity and of the environmental cues provided in vivo. Secondary structure predictions of tau variants revealed that the insertion of the exon 3-encoded domain substantially modifies the secondary structure of the N-terminal region of tau. This N-terminal heterogeneity may confer distinct regulatory roles on the tau variants during ontogeny and may contribute to plasticity in the adult rat brain.
Tau蛋白变体是轴突微管相关磷蛋白，其表达与发育调控的神经突生长相关。单个基因通过复杂的可变剪接编码多种tau转录本。我们研究了编码tau N端变体的mRNA的表达，并显示成年大鼠神经组织（包括内耳、海马体、皮质、纹状体、脑干、小脑、嗅球和视网膜）中外显子2和3存在明显的可变剪接。然后，我们使用逆转录酶偶联聚合酶链反应和原位杂交技术，将发育研究聚焦于体内和体外的海马神经元，以探讨编码tau N端变体的可变剪接mRNA的发育和空间表达。不含外显子2和3的tau mRNA在整个发育过程中都存在，尽管其水平在成年期有所下降。那些含有外显子2但不含外显子3的mRNA在新生大鼠的海马体中已经存在，并且在出生后的第一周内其水平升高，主要在锥体细胞层。含有外显子2和3的tau RNA在此阶段末期出现在锥体细胞层和齿状颗粒细胞中。含有外显子2的mRNA似乎与正在进行轴突发芽的细胞相关，而含有外显子3的RNA则在已建立连接的成熟神经元中表达。tau可变剪接的时间和模式在培养的海马神经元中得以维持，这表明剪接过程独立于体内提供的有组织的连接性和环境线索。tau变体的二级结构预测表明，外显子3编码结构域的插入显著改变了tau N端区域的二级结构。这种N端异质性可能在个体发育过程中赋予tau变体不同的调控作用，并可能有助于成年大鼠大脑的可塑性。
