Aubry M, Maness P F
Department of Biochemistry, University of North Carolina, School of Medicine, Chapel Hill, NC 27514.
J Neurosci Res. 1988 Oct-Dec;21(2-4):473-9. doi: 10.1002/jnr.490210238.
Proteins phosphorylated at tyrosine residues in the developing rat brain have been identified with a focus on the nerve growth cone and synaptic terminal. Endogenous protein phosphorylation in membranes from a subcellular growth cone fraction of fetal rat brain revealed prominent 55-60 kD phosphotyrosine-containing proteins. Proteins of similar size were recognized by phosphotyrosine antibodies in isolated growth cone membranes, indicating that they contained phosphotyrosine in vivo. Proteins of 55-60 kD were not highly phosphorylated in synaptosomes from adult brain, suggesting a growth cone-specific function. Generally, tyrosine phosphorylation was much lower in adult brain than in fetal brain fractions. Although some synaptosomal membrane proteins that contained phosphotyrosine corresponded in size with those in growth cone membranes (92 kD, 41 kD), others were unique to synaptosomal membranes (38 kD and 30 kD). Immunoperoxidase staining of fetal rat neocortex with phosphotyrosine antibodies at embryonic day 19 revealed immunoreactivity in presumptive migratory neuroblasts in the intermediate zone and in processes of the molecular layer. Proliferating neuroepithelial cells of the ventricular zone showed little immunoreactivity. Lower levels of phosphotyrosine immunoreactivity were seen until postnatal day 10, correlating with the period of maximal process outgrowth. These results indicate that protein tyrosine phosphorylation in the developing nervous system may be functionally significant in an aspect of neuronal differentiation such as growth cone-mediated process extension and cell migration. An analogous role in the mature brain may be related to synaptic plasticity or function.
已鉴定出发育中大鼠大脑中酪氨酸残基磷酸化的蛋白质，重点关注神经生长锥和突触终末。来自胎鼠大脑亚细胞生长锥部分的膜内源性蛋白质磷酸化显示，有突出的55 - 60 kD含磷酸酪氨酸的蛋白质。在分离的生长锥膜中，磷酸酪氨酸抗体识别出大小相似的蛋白质，表明它们在体内含有磷酸酪氨酸。55 - 60 kD的蛋白质在成体大脑的突触体中磷酸化程度不高，提示其具有生长锥特异性功能。一般来说，成体大脑中的酪氨酸磷酸化水平远低于胎脑部分。虽然一些含磷酸酪氨酸的突触体膜蛋白大小与生长锥膜中的对应蛋白（92 kD、41 kD）一致，但其他一些蛋白是突触体膜特有的（38 kD和30 kD）。在胚胎第19天用磷酸酪氨酸抗体对胎鼠新皮层进行免疫过氧化物酶染色，显示中间带推定的迁移神经母细胞和分子层的突起中有免疫反应性。脑室区增殖的神经上皮细胞显示出很少的免疫反应性。直到出生后第10天，磷酸酪氨酸免疫反应性水平较低，这与最大突起生长时期相关。这些结果表明，发育中的神经系统中蛋白质酪氨酸磷酸化在神经元分化的一个方面可能具有功能意义，如生长锥介导的突起延伸和细胞迁移。在成熟大脑中的类似作用可能与突触可塑性或功能有关。
