Local environmental cues are indispensable for axonal growth and guidance during brain circuit formation. Here, we combine genetic and pharmacological tools, as well as systems neuroanatomy in human fetuses and mouse models, to study the role of endocannabinoid and Slit/Robo signalling in axonal growth. We show that excess 2-arachidonoylglycerol, an endocannabinoid affecting directional axonal growth, triggers corpus callosum enlargement due to the errant CB1 cannabinoid receptor-containing corticofugal axon spreading. This phenotype mechanistically relies on the premature differentiation and end-feet proliferation of CB2R-expressing oligodendrocytes. We further show the dependence of both axonal Robo1 positioning and oligodendroglial Slit2 production on cell-type-specific cannabinoid receptor activation. Accordingly, Robo1 and/or Slit2 manipulation limits endocannabinoid modulation of axon guidance. We conclude that endocannabinoids can configure focal Slit2/Robo1 signalling to modulate directional axonal growth, which may provide a basis for understanding impaired brain wiring associated with metabolic deficits and prenatal drug exposure.
Bibliographical noteThis work was supported by the Swedish Medical Research Council (T.H.), Swedish Brain Research Foundation (‘Hjärnfonden’; T.H.), Novo Nordisk Foundation (T.H.), Petrus & Augusta Hedlunds’ Foundation (T.H.), EU-FP7 project DEVELAGE (N278486, G.G.K.), National Brain Research Program of the Hungarian Academy of Sciences (A.A.), National Institutes of Health (DA023214, T.H. and Y.L.H.; DA030359, Y.L.H; F31-DA031559, C.V.M.) and the Wellcome Trust (#089775, J.G.P. and W.D.A.). The content of this report is solely the responsibility of the authors and does not necessarily represent the official views of the US National Institutes of Health. We thank M. Watanabe, K. Mackie and F. Murakami for antibodies, Y.A. Barde for taugfp/+ mice, K. Mackie for MGL−/− tissues, F. Molina-Holgado for the oligodendrocyte isolation protocol, O.K. Penz for technical assistance, M. Tessier-Lavigne, L. Erskine, R.A. Ross and members of the Harkany laboratory for discussions and feedback and the National Institute of Mental Health for the transfer of CB1R−/− colony founders. Laser-scanning microscopy was performed at the Click Imaging Core Facility of the Karolinska Institutet
- Cell signalling
- Development of the nervous system
- Neuronal physiology
- Receptor, Cannabinoid, CB1