Down-regulation of membrane glycoprotein in amoeboid microglia transforming into ramified microglia in postnatal rat brain

Abstract

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.

Migration and Proliferation of Motile Immature Glial Cells in the Developing Cerebral Cortex of Infantile Rat.

“…After P28, in the double staining examination, it was difficult to detect microglial cells with IB4 immunohistochemistry because of its reduced intensity, in accordance with the findings of Wu et al [38], while the same cell showed strong immunostaining with anti-Tb4 antibody. To the contrary, blood vessels were always strongly IB4 positive in any age group.…”

“…However, Tb4 immunoreactive cells have not been well investigated in the developing rat brain. On the other hand, IB4 is known as a common marker for microglia [22,34], although it has been pointed out that detection of microglial cells with IB4 becomes gradually difficult with their maturation [38]. We studied Tb4 immu- nohistochemistry of cortical cells in comparison with IB4 in developing rat brain.…”

Region-specific activation of microglial cells in the rat septal complex following fimbria-fornix transection

“…Labeling with GSA I-B 4 is widely accepted to stain microglial cells at both light and electron microscopic levels (e.g., Streit and Kreutzberg, 1987;Marty et al, 1991;Riva-Depaty et al, 1994;Wu et al, 1994). However, the stainability of microglial cells strongly depends on their activation.…”

The origin and differentiation of microglial cells during development

“…An immunocytochemical study by Wu et al (1994) described gradual modi®cations (downregulation) in the membrane glycoprotein(s) recognized by the isolectin B 4 of Bandeiraea simplicifolia during transformation of ameboid microglia into rami®ed microglia. The labeling of rami®ed microglia with this lectin was weaker than that of brain macrophages.…”