Phosphoinositide detection at synapses of fixed murine hippocampal neurons.

The minor phospholipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is crucial for neurotransmission and has been implicated in Parkinson's disease. Here, we present a staining protocol for the analysis of activity-dependent changes of PI(4,5)P2 at synapses. We describe steps for stimulating and fixing murine hippocampal neurons, staining with probes for PI(4,5)P2 and a synaptic marker, and analysis by high-resolution microscopy. Our approach gives insights into local PI(4,5)P2 synthesis and turnover at synapses and can be extended to phosphoinositide lipids other than PI(4,5)P2. For complete details on the use and execution of this protocol, please refer to Bolz et al.1.

Synaptotagmin 1-triggered lipid signaling facilitates coupling of exo- and endocytosis.

Exocytosis and endocytosis are essential physiological processes and are of prime importance for brain function. Neurotransmission depends on the Ca2+-triggered exocytosis of synaptic vesicles (SVs). In neurons, exocytosis is spatiotemporally coupled to the retrieval of an equal amount of membrane and SV proteins by compensatory endocytosis. How exocytosis and endocytosis are balanced to maintain presynaptic membrane homeostasis and, thereby, sustain brain function is essentially unknown. We combine mouse genetics with optical imaging to show that the SV calcium sensor Synaptotagmin 1 couples exocytic SV fusion to the endocytic retrieval of SV membranes by promoting the local activity-dependent formation of the signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at presynaptic sites. Interference with these mechanisms impairs PI(4,5)P2-triggered SV membrane retrieval but not exocytic SV fusion. Our findings demonstrate that the coupling of SV exocytosis and endocytosis involves local Synaptotagmin 1-induced lipid signaling to maintain presynaptic membrane homeostasis in central nervous system neurons.