Pierre K, Rougon G, Allard M, Bonhomme R, Gennarini G, Poulain D A, Theodosis D T
Institut National de la Santé et de la Recherche Médicale U378 Neurobiologie Morphofonctionelle, Institut François Magendie, F33077 Bordeaux Cedex, France.
J Neurosci. 1998 Jul 15;18(14):5333-43. doi: 10.1523/JNEUROSCI.18-14-05333.1998.
F3, a glycoprotein of the immunoglobulin superfamily implicated in axonal growth, occurs in oxytocin (OT)-secreting and vasopressin (AVP)-secreting neurons of the adult hypothalamo-neurohypophysial system (HNS) whose axons undergo morphological changes in response to stimulation. Immunocytochemistry and immunoblot analysis showed that during basal conditions of HNS secretion, there are higher levels of this glycosylphosphatidyl inositol-anchored protein in the neurohypophysis, where their axons terminate, than in the hypothalamic nuclei containing their somata. Physiological stimulation (lactation, osmotic challenge) reversed this pattern and resulted in upregulation of F3 expression, paralleling that of OT and AVP under these conditions. In situ hybridization revealed that F3 expression in the hypothalamus is restricted to its magnocellular neurons and demonstrated a more than threefold increase in F3 mRNA levels in response to stimulation. Confocal and electron microscopy localized F3 in secretory granules in all neuronal compartments, a localization confirmed by detection of F3 immunoreactivity in granule-enriched fractions obtained by sucrose density gradient fractionation of rat neurohypophyses. F3 was not visible on any cell surface in the magnocellular nuclei. In contrast, in the neurohypophysis, it was present not only in secretory granules but also on the surface of axon terminals and glia and in extracellular spaces. Taken together, our observations reveal that the cell adhesion glycoprotein F3 is colocalized with neurohypophysial peptides in secretory granules. It follows, therefore, the regulated pathway of secretion in HNS neurons to be released by exocytosis at their axon terminals in the neurohypophysis, where it may intervene in activity-dependent structural axonal plasticity.
F3是一种免疫球蛋白超家族的糖蛋白，与轴突生长有关，存在于成年下丘脑-神经垂体系统（HNS）中分泌催产素（OT）和抗利尿激素（AVP）的神经元中，其轴突会因刺激而发生形态变化。免疫细胞化学和免疫印迹分析表明，在HNS分泌的基础状态下，这种糖基磷脂酰肌醇锚定蛋白在神经垂体（其轴突在此终止）中的水平高于含有其胞体的下丘脑核。生理刺激（哺乳、渗透压挑战）逆转了这种模式，导致F3表达上调，与这些条件下OT和AVP的表达上调情况相似。原位杂交显示，下丘脑F3的表达仅限于其大细胞神经元，并表明在刺激后F3 mRNA水平增加了三倍多。共聚焦显微镜和电子显微镜将F3定位在所有神经元区室的分泌颗粒中，通过对大鼠神经垂体进行蔗糖密度梯度分级分离得到的富含颗粒的组分中检测到F3免疫反应性，证实了这一定位。在大细胞核的任何细胞表面均未观察到F3。相反，在神经垂体中，它不仅存在于分泌颗粒中，还存在于轴突终末和神经胶质细胞的表面以及细胞外间隙中。综上所述，我们的观察结果表明，细胞黏附糖蛋白F3与神经垂体肽共定位于分泌颗粒中。因此，它遵循HNS神经元的分泌调节途径，通过胞吐作用在神经垂体的轴突终末释放，在那里它可能参与依赖活动的轴突结构可塑性。
