Olive S, Rougon G, Pierre K, Theodosis D T
Laboratoire de Génétique et Physiologie du Développement, CNRS UMR 9943, Parc Scientifique de Luminy, Marseille, France.
Brain Res. 1995 Aug 21;689(2):271-80. doi: 10.1016/0006-8993(95)00555-5.
The F3 cell surface glycoprotein consists of six immunoglobulin-like domains, four fibronectin type III repeats and a glycosylphosphatidylinositol anchor and is found in membrane-bound and soluble form. Until now, it has been localized mainly on axons of subsets of developing and postnatal neurons and has been implicated in axonal growth and synaptogenesis. We here examined its expression in the adult rat hypothalamo-neurohypophysial system composed of magnocellular neurons whose axons can undergo remodelling in adulthood in response to lesion or physiological stimulation. Immunoblot analyses demonstrated high levels of F3 immunoreactivity in the hypothalamic nuclei containing the somata of the neurons, in the median eminence, through which pass their axons and in the neurohypophysis, where they terminate. The amount of F3 detected in the latter was 2-fold that in the hypothalamus. In addition, soluble forms predominated in the neurohypophysis and GPI-linked forms in the hypothalamus. Immunocytochemistry revealed a strong F3 immunoreactivity throughout the neurohypophysis and internal layer of the median eminence, characterized by a punctate labeling of fibers and dense filling of dilatations. In the hypothalamic nuclei, staining of variable intensity was visible in the cytoplasm of some magnocellular somata. In contrast, in colchicine-treated rats, all magnocellular somata throughout the hypothalamus displayed intense labeling while staining in the neurohypophysis was greatly reduced. Our observations reveal that neurons of the adult hypothalamo-neurohypophysial system express high level of F3, even under normal conditions. In view of its distribution and the differing proportions of membrane-bound and soluble forms, we propose that, after synthesis in the hypothalamus, F3 is targeted to the neurohypophysis where it accumulates in neurosecretory terminals or is released into the extracellular space. It remains to be seen whether its expression is linked to the secretion of the neurohypophysial peptides and in particular, to the ability of these neurons to undergo structural remodelling in adulthood.
F3细胞表面糖蛋白由六个免疫球蛋白样结构域、四个纤连蛋白III型重复序列和一个糖基磷脂酰肌醇锚组成，以膜结合形式和可溶性形式存在。到目前为止，它主要定位于发育中和出生后神经元亚群的轴突上，并与轴突生长和突触形成有关。我们在此研究了它在成年大鼠下丘脑-神经垂体系统中的表达，该系统由大细胞神经元组成，其轴突在成年期可因损伤或生理刺激而发生重塑。免疫印迹分析表明，在含有神经元胞体的下丘脑核、轴突从中穿过的正中隆起以及轴突终末所在的神经垂体中，F3免疫反应性水平很高。在神经垂体中检测到的F3量是下丘脑中的两倍。此外，可溶性形式在神经垂体中占主导，而糖基磷脂酰肌醇连接形式在下丘脑中占主导。免疫细胞化学显示，整个神经垂体和正中隆起内层有强烈的F3免疫反应性，其特征是纤维呈点状标记，扩张处密集填充。在下丘脑核中，一些大细胞胞体的细胞质中可见强度不一的染色。相比之下，在秋水仙碱处理的大鼠中，整个下丘脑的所有大细胞胞体都显示出强烈的标记，而神经垂体中的染色则大大减少。我们的观察结果表明，即使在正常条件下，成年下丘脑-神经垂体系统的神经元也表达高水平的F3。鉴于其分布以及膜结合形式和可溶性形式的不同比例，我们提出，F3在下丘脑合成后，被靶向运输到神经垂体，在那里它积聚在神经分泌终末或释放到细胞外空间。其表达是否与神经垂体肽的分泌有关，特别是与这些神经元在成年期进行结构重塑的能力有关，还有待观察。
