Shooting by laser beam activates growth cones of neurons transfected with PI3K photoswitch.

In TV games, kids shoot monsters or aliens by a laser beam, and they may get bonus points. Now, we can control growth-cone motility of neuronal cells by shooting the tips of neurites with blue laser beam.

We made this system not for fun, but to understand the basic mechanisms of neuronal growth and the primary function of PI3K. PI3K (phosphatidyl inositol3 kinase) is a multifunctional enzyme which produces PIP3 and is involved in the mechanisms of multiple diseases, including cancer metastasis, and Diabetes Mellitus. We developed blue light switchable PI3K by making a hybrid with plant proteins. The PI3K photoswitch enabled us to analyze its function at high spatiotemporal resolution, which may make us possible to specify primary roles of the PI3K in the neuronal development.

Please watch our movie. Neurons grow several processes called neurites. Growth-cone is a highly motile, hand-like structure at the tips of neurites, which consists of peripheral area with finger-like filopodia or lamelipodia and palm-ilke central area. We found that laser beam specifically increased the PIP3 (pseudo color) and activated the motility of peripheral growth cone of the photoswitch -transfected neurons. The movie shows that one process was chosen and its tip was irradiated by blue laser beam (red circle, Notice that you cannot see blue light ). Then, another tip was shot by the laser beam (second red circle), resulted in PIP3 accumulation and high motility.
We found that PI3K and its product PIP3 were sufficient to induce the peripheral, actin based part of growthcones. Using the probe, we further studied the fundamental aspect of PI3K signaling. For details, please see our recent publication.  T. Kakumoto, T. Nakata. Optogenetic Control of PIP3: PIP3 Is Sufficient to Induce the Actin-Based Active Part of Growth Cones and Is Regulated via Endocytosis. PLOS ONE 8(8): e70861. 2013.