Proceedings of The Physiological Society
King's College London (2011) Proc Physiol Soc 22, C17
A cannabinoid-RalA signalling pathway controlling neural precursor migration
S. Gajendra1, M. Oudin1, P. Doherty1, G. Lalli1
1. Wolfson CARD, King's College London, London, United Kingdom.
In the mammalian brain, neural precursors derived from neural stem cells residing in the subventricular zone migrate towards the olfactory bulb following a very well defined path, the rostral migratory stream (RMS). Importantly, these precursors have the capacity to migrate away from their native route to areas of pathological damage in the adult brain (1). While our understanding of neural precursor migration has increased over the years, the exact molecular mechanisms remain to be fully elucidated. Understanding the migratory properties of these cells is essential to fully exploit their potential in neuroregenerative strategies. The endocannabinoid system has been previously shown to play an important role in the regulation of neural stem cell proliferation. We have recently shown that it is also involved in controlling the migration of RMS precursors both in vitro and in vivo (2). Indeed, agonists of the G protein-coupled cannabinoid receptors CB1 and CB2 markedly increase neural precursor migration, while CB receptor antagonists significantly impair it. In an effort to analyse the CB-dependent signalling pathways regulating neural precursor motility, we find that stimulation of CB1/CB2 receptors leads to a significant activation of RalA, a Ras-like GTPase previously shown to be involved in the control of neuronal morphology and polarity (3,4). RalA appears to be abundantly expressed in a vesicular pattern in migrating neural precursors. Using time-lapse imaging of RMS explants, we show that siRNA-mediated knockdown of RalA abolishes cannabinoid-stimulated motility and strongly impairs nucleokinesis, a crucial step for efficient migration. Current work is aimed at dissecting the molecular components of this cannabinoid-RalA signalling pathway, including other small GTPases and regulators of nuclear movement. In addition, our preliminary data suggest that other factors known to stimulate neural precursor migration can also activate RalA. We are currently examining the effect of RalA knockdown on neural precursor migration in vivo using electroporation of shRNA-expressing plasmids in the postnatal mouse forebrain together with time-lapse imaging of fluorescently labelled precursors in cultured brain slices.
Where applicable, experiments conform with Society ethical requirements