主题：Deciphering the origins of repopulated microglia in the central nervous system
报告人：彭勃 博士，中国科学院深圳先进技术研究院 ，副研究员、课题组长
New-born microglia rapidly replenish the whole brain after selective elimination of most microglia (>99%) in adult mice. Previous studies reported that repopulated microglia were largely derived from microglial progenitor cells expressing Nestin in the brain. However, the origin of these repopulated microglia has been hotly debated. In this study, we investigated the origin of repopulated microglia by a series of fate mapping approaches. We first excluded the blood origin of repopulated microglia via parabiosis. With different transgenic mouse lines, we then demonstrated that all repopulated microglia were derived from the proliferation of the few surviving microglia (<1%). Though with a transient pattern of Nestin expression in newly forming microglia, none of repopulated microglia was derived from Nestin-positive non-microglial cells. In summary, we conclude that repopulated microglia are solely derived from residual microglia rather than de novo progenitors, suggesting for the absence of microglial progenitor cells in the adult brain.
In addition to repopulated brain microglia, we investigated the origins of repopulated microglia in the retina and found that the repopulated retinal microglia were not derived from the residual microglia in the retina. Instead, they had two distinct origins: the center-emerging microglia were derived from residual microglia in the optic nerve and the periphery-emerging microglia were derived from macrophages in the ciliary body/iris. Therefore, we identified novel origins of retinal microglia by using a model of microglial repopulation. Our findings expand the understanding on the origins of microglia in the retina.