The human nervous system is composed of approximately 100 billion neurons, which form an intricate network containing over 10 trillion synapses. Functionality of neural circuits therefore hinges upon neuronal axons finding their synaptic targets. Proper assembly of neuronal circuits during development is mediated by specialized sensory-motile structures located at the tips of extending axons known as growth cones. In this study, we elucidate how growth cones penetrate through tissues to reach their synaptic targets using laser scanning confocal microscopy (LSCM) and structured illumination microscopy (SIM). We have recently shown that during development, neural growth cones form protrusions on their apical and basal surfaces that are structurally and molecularly similar to cancer cell invadosomes. Invadosomes are cellular protrusions rich in filamentous actin (F-actin) capable of ECM degradation, and promote cell invasion and motility. During early development, neural growth cones exhibit invadosome-like protrusions. However, the exact mechanism by which nascent invadosomes stabilize and mature are currently unknown. Here, we determined which signaling membrane phosphoinositides in the membrane are enriched at invadosomes. Cultured spinal cord axons from Xenopus embryos expressing the markers for F-actin together with PI(3,4)P2 or PI(3,4,5)P3 were imaged live. Our findings indicate that while PI(3,4)P2 exhibits no enrichment at actin puncta, while PI(3,4,5)P3 does co-localize with certain actin puncta. PI(3,4,5)P3 may thus play a greater role in growth cone invadosomes. In addition, we treated developing neurons with inhibitors of SHIP2 and PI3K, enzymes that enrich local PI(3,4)P2 and PI(3,4,5)P3, respectively. Understanding the involvement of signaling membrane phosphoinositides in the maturation of invadosomes provides insight into how neurons grow during development and reach their targets.

Role of signaling lipid phosphoinositides PI(3,4,5)P3 and PI(3,4)P2 In neural growth cone invadosomes

255th National Meeting (2018)

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