San José I, Vázquez E, García-Atarés N, Rodriguez S, Vega J A, Represa J
Departamento de Anatomía Humana, Facultad de Medicina, Universidad de Valladolid, Spain.
Anat Embryol (Berl). 1997 Mar;195(3):299-310. doi: 10.1007/s004290050049.
Microtubule-associated proteins (MAPs) are essential cytoskeletal components during development for neurogenesis and neuronal plasticity. Inner ear innervation is accomplished by cochleovestibular ganglion (CVG) neurons in a highly specific, well-defined pattern, which is regulated by neurotrophic factors belonging to the neurotrophin family. The inner ear offers a suitable model for studying the expression of MAPs and assessing their role in neurotrophin-induced effects that are required for neuron-target innervation. The present study was undertaken to analyze the expression and localization of MAP5 isoforms during development of CVG neurons in vivo an in vitro; as well as the regulation of MAP5 by neurotrophin-3 (NT3) in cell culture. MAP5 expression in the inner ear of chick embryos and postnatal specimens was monitored using immunoblots and immunohistochemistry on frozen sections. MAP5 was highly expressed during the early stages of CVG development, at embryonic day (E)4, being located in both neuronal perikarya and neurites. Expression was maintained during the neurite outgrowth phase (E6-E12), when strong MAP5 immunostaining was observed at the same cellular locations. MAP5 expression decreased suddenly at E14, after the establishment of specific connections between the CVG neurons and their targets, the sensory epithelium of the inner ear. In cultured CVG neurons addition of NT3 led to increased MAP5 expression and produced neurite outgrowth. Both effects are differentially regulated in parallel by low (0.5 ng/ml) and high (5 ng/ml) NT3 concentrations. Present results suggest that MAP5 may be involved in neurotrophin-induced microtubule bundling during neurite outgrowth of auditory neurons.
微管相关蛋白（MAPs）是发育过程中神经发生和神经元可塑性所必需的细胞骨架成分。内耳神经支配由蜗神经节（CVG）神经元以高度特异性、明确的模式完成，这受神经营养因子家族中的神经营养因子调节。内耳为研究MAPs的表达及其在神经元与靶标神经支配所需的神经营养因子诱导效应中的作用提供了一个合适的模型。本研究旨在分析体内和体外CVG神经元发育过程中MAP5亚型的表达和定位；以及细胞培养中神经营养因子-3（NT3）对MAP5的调节。通过对冷冻切片进行免疫印迹和免疫组织化学，监测鸡胚和出生后标本内耳中MAP5的表达。MAP5在CVG发育的早期阶段，即胚胎第（E）4天高度表达，位于神经元胞体和神经突中。在神经突生长阶段（E6-E12）表达持续存在，此时在相同细胞位置观察到强烈的MAP5免疫染色。在CVG神经元与内耳感觉上皮这一靶标建立特定连接后，MAP5表达在E14突然下降。在培养的CVG神经元中添加NT3导致MAP5表达增加并产生神经突生长。低（0.5 ng/ml）和高（5 ng/ml）NT3浓度对这两种效应的调节存在差异且相互平行。目前的结果表明，MAP5可能参与听觉神经元神经突生长过程中神经营养因子诱导的微管成束。
