Regulation of invadosome-mediated peripheral axon guidance by ErbB signaling

ABSTRACT The development of the nervous system requires the proper differentiation, migration, morphogenesis and maturation of neurons. The morphological differentiation of individual neurons and the assembly of the trillions of neuronal connections that compose the human nervous system occurs through guided extension of axons and dendrites. While many studies have investigated the molecular mechanisms that regulate axon guidance over two-dimensional substrata in vitro or along axonal tracks in vivo, little is known about cues that control axon guidance across three-dimensional tissues and through basement membranes. These are fundamental questions as numerous distinct types of axons must penetrate basement membranes to enter diverse tissue targets. Our preliminary and recently published data suggest that along with planar filopodia and lamellipodia, growth cones generate orthogonal protrusions in vitro and in vivo that resemble podosomes or invadopodia. Podosomes and invadopodia, collectively referred to as invadosomes, are distinct actin-based cellular protrusions associated with extracellular matrix (ECM) degradation and tissue invasion. We hypothesize that distinct ligands in the environment of growth cones promote invadosome formation, maturation and function. Further, we hypothesize that mature invadosomes use microtubules to target matrix metalloproteases (MMPs) to their cell surface and support local MMP secretion. Several compelling pieces of preliminary data suggest that EGF ligands (EGF and Neuregulins), promote invadosome formation and maturation by motor and Rohon Beard neuron growth cones, leading to ECM remodeling by MMPs and axon exiting the spinal cord. The three aims of this proposal will use a series of molecular gain of function and loss of function manipulations, together with live and fixed cell fluorescence imaging in vitro and in vivo, to assess the receptors/ligands, as well as the signals, that control invadosome formation and their roles in driving peripheral axon exiting the spinal cord.