Wu C H, Wen C Y, Shieh J Y, Ling E A
Department of Anatomy, College of Medicine, National Taiwan University, Taipei.
J Neurocytol. 1994 Apr;23(4):258-69. doi: 10.1007/BF01275530.
The present study describes the ultrastructural localization and labelling pattern of lectin in different microglial cell phenotypes in the postnatal rat brain using the isolectin, GSA I-B4. The nascent round and amoeboid microglial cells (round cells and cells displaying short processes) were labelled at their cytoplasmic membrane and the membrane of the subplasmalemmal vacuoles. In the course of their transformation into ramified forms with age, dense lectin labelling was observed successively at different sites in the differentiating cells. The most striking feature was the staining of the Golgi saccules on the trans face, the trans tubular network and associated vesicles and vacuoles in the 'intermediate' ramified microglia (ramified cells bearing thick and long processes and those with thin and long processes). The vacuoles with accumulated reaction products were closely associated with many microtubules extending into the cytoplasmic processes. At the surface, the lectin-labelled vacuoles and vesicles appeared to fuse with the membrane and their contents communicated with the exterior. In the advanced or most differentiated ramified microglial cells (cells bearing attenuated processes), the lectin staining at all the above mentioned sites became diminished. In conclusion, in the transformation of the round microglia into their ramified derivatives, the glycoconjugates at the cytoplasmic membrane are progressively reduced. It is postulated from this study that the down-regulation of the glycoconjugates of the microglial plasma membrane is due primarily to their internalization during endocytosis. This process would trigger a de novo galactosyl protein synthesis and/or modification at the trans Golgi saccules and trans tubular network probably in an attempt to degrade the internalized membrane glycoproteins or to replenish the consumption of the membrane glycoconjugates.
本研究利用异凝集素GSA I-B4描述了出生后大鼠脑中不同小胶质细胞表型中凝集素的超微结构定位和标记模式。新生的圆形和阿米巴样小胶质细胞（圆形细胞和显示短突起的细胞）在其细胞质膜和质膜下空泡的膜上被标记。随着年龄增长，它们转变为分支状形态的过程中，在分化细胞的不同部位相继观察到密集的凝集素标记。最显著的特征是在“中间”分支状小胶质细胞（具有粗长突起和细长突起的分支状细胞）中，反面高尔基体囊泡、反面管状网络以及相关的囊泡和空泡被染色。积累反应产物的空泡与许多延伸到细胞质突起中的微管紧密相关。在表面，凝集素标记的空泡和囊泡似乎与膜融合，其内容物与外部相通。在晚期或最分化的分支状小胶质细胞（具有变细突起）中，上述所有部位的凝集素染色都减弱。总之，在圆形小胶质细胞向其分支状衍生物的转变过程中，细胞质膜上的糖缀合物逐渐减少。本研究推测，小胶质细胞质膜糖缀合物的下调主要是由于它们在胞吞作用期间被内化。这个过程可能会触发反式高尔基体囊泡和反式管状网络中半乳糖基蛋白的从头合成和/或修饰，可能是为了降解内化的膜糖蛋白或补充膜糖缀合物的消耗。
