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Immunohistochemical detection of thrombospondin in microglia in the developing rat brain
B Chamak1, A Dobbertin, M Mallat
1INSERM U114, Collège de France, Paris, France.
Abstract:
The development of microglia involves the expression of a phenotype displaying phagocytic behaviour termed brain macrophage or amoeboid microglial cell. We have previously shown that rat brain macrophages purified in vitro secrete thrombospondin, an extracellular matrix protein, which acts on cultured neuronal cells by promoting neurite growth. In the present study, the expression of thrombospondin was investigated in tissue sections of the developing rat forebrain in relation to the distribution of microglia. These cells were identified using anti-macrophage antibodies and the isolectin B4 from Bandeiraea simplicifolia. Immunocytochemical detection of thrombospondin clearly outlined a cell population displaying the morphologies and distribution of brain macrophages, from the 17th day of embryonic life up to the end of the second postnatal week. These cells were most numerous in cortical and subcortical regions of developing fibre tracts such as the corpus callosum or the internal capsule. The localization of thrombospondin in brain macrophages was confirmed by double immunostaining using ED1 monoclonal anti-macrophage antibodies. Ramified microglial cells were also labelled transiently by anti-thrombospondin antibodies during early postnatal life. These results provide in situ evidence supporting the notion that microglial cells could favour axonal growth by producing thrombospondin during development.
Insights
Microglia, or brain macrophages, produce thrombospondin during rat brain development. This protein supports neurite growth, suggesting microglia promote axonal development.
Area of Science:
- Neuroscience
- Developmental Biology
- Immunology
Background:
- Microglia, the brain's resident immune cells, exhibit phagocytic behavior during development, termed brain macrophages.
- Previous research indicated rat brain macrophages secrete thrombospondin, an extracellular matrix protein that promotes neurite growth in neurons.
Purpose of the Study:
- To investigate the expression and localization of thrombospondin in developing rat brain tissue.
- To correlate thrombospondin distribution with the presence and morphology of microglia.
Main Methods:
- Immunocytochemistry was used to detect thrombospondin in tissue sections of the developing rat forebrain.
- Microglia were identified using anti-macrophage antibodies and Bandeiraea simplicifolia isolectin B4.
- Double immunostaining with ED1 monoclonal antibodies confirmed thrombospondin localization in brain macrophages.
Main Results:
- Thrombospondin expression was observed in brain macrophages from embryonic day 17 through the second postnatal week.
- These thrombospondin-expressing cells were abundant in developing fibre tracts like the corpus callosum and internal capsule.
- Ramified microglial cells also showed transient labeling with anti-thrombospondin antibodies postnatally.
Conclusions:
- In situ evidence supports that microglia produce thrombospondin during brain development.
- Microglial thrombospondin production may facilitate axonal growth in the developing central nervous system.
