Phospholipids are asymmetrically distributed at the plasma membrane. Phosphatidylserine (PtdSer) is exclusively located in the inner leaflet of the cell membrane while phosphatidylcholine (PtdCho) and glycolipids are mainly located in the outer leaflet of the membrane. However, this asymmetry is disrupted in various physiological situations, and PtdSer is exposed on the cell surface. In platelets, exposed PtdSer functions as a scaffold for the coagulation reaction, while in dead cells, exposed PtdSer serves as an “Eat-me” signal for efferocytosis. In the developing brain, synaptic connections are over-formed during the fetal period, but about half of the neurons are removed by apoptosis, and synaptic and dendritic compartments of living neurons are also removed by phagocytes. During these processes, glial cells such as microglia and astrocyte engulf unwanted dead cells and compartments in living cells using several phagocytic receptors, recognizing PtdSer by direct binding or an indirect way using secreted molecules. Based on recent findings, we will discuss how the compartments in living neurons are eliminated for the neuronal circuit plasticity.

磷脂在质膜上不对称分布。磷脂酰丝氨酸 (PtdSer) 仅位于细胞膜的内小叶中，而磷脂酰胆碱 (PtdCho) 和糖脂主要位于细胞膜的外小叶中。然而，这种不对称性在各种生理情况下被破坏，PtdSer 暴露在细胞表面。在血小板中，暴露的 PtdSer 充当凝血反应的支架，而在死细胞中，暴露的 PtdSer 充当胞吞作用的“Eat-me”信号。在发育中的大脑中，突触连接在胎儿时期过度形成，但大约一半的神经元被细胞凋亡去除，活神经元的突触和树突隔室也被吞噬细胞去除。在这些过程中，胶质细胞（如小胶质细胞和星形胶质细胞）使用几种吞噬细胞受体吞噬不需要的死细胞和活细胞中的隔室，通过直接结合或使用分泌分子的间接方式识别 PtdSer。根据最近的发现，我们将讨论如何消除活神经元中的隔室以实现神经元回路的可塑性。