Optogenetic Control of PIP(3): PIP(3) Is Sufficient to Induce the Actin-Based Active Part of Growth Cones and Is Regulated via Endocytosis

Phosphatidylinositol-3,4,5-trisphosphate (PIP(3)) is highly regulated in a spatiotemporal manner and plays multiple roles in individual cells. However, the local dynamics and primary functions of PIP(3) in developing neurons remain unclear because of a lack of techniques for manipulating PIP(3) spatiotemporally. We addressed this issue by combining optogenetic control and observation of endogenous PIP(3) signaling. Endogenous PIP(3) was abundant in actin-rich structures such as growth cones and “waves”, and PIP(3)-rich plasma membranes moved actively within growth cones. To study the role of PIP(3) in developing neurons, we developed a PI3K photoswitch that can induce production of PIP(3) at specific locations upon blue light exposure. We succeeded in producing PIP(3) locally in mouse hippocampal neurons. Local PIP(3) elevation at neurite tips did not induce neurite elongation, but it was sufficient to induce the formation of filopodia and lamellipodia. Interestingly, ectopic PIP(3) elevation alone activated membranes to form actin-based structures whose behavior was similar to that of growth-cone-like “waves”. We also found that endocytosis regulates effective PIP(3) concentration at plasma membranes. These results revealed the local dynamics and primary functions of PIP(3), providing fundamental information about PIP(3) signaling in neurons.