Endocannabinoids Regulate Cerebellar Granule Cell Differentiation

Abstract

The cerebellum plays a crucial role in learning and execution of complex automated behaviors, including fine motor skills, language, and emotional regulation. Cerebellar development continues throughout an extended postnatal period. The most numerous neurons in the cerebellum, as well as the entire brain, are the cerebellar granule cells (GCs), which are generated in a dedicated secondary proliferative zone, the external granule cell layer (EGL), during the first three postnatal weeks in mice, and over a year in humans. The robust expansion of granule cells during early development is responsible for the majority of cerebellar expansion. Morphological and molecular changes that drive GC proliferation and differentiation have been extensively characterized, starting from the developmental studies by Santiago Ramón y Cajal. GC progenitors (GCPs) proliferate in the outer EGL (oEGL). As they are pushed into the inner EGL (iEGL) by the newly generated GCPs, they exit the cell cycle and begin differentiation, first extending bipolar neurites, followed by tangential migration, and eventually radial migration to the inner granule cell layer (IGL), their target territory. Deregulation of GCPs expansion, proliferation to differentiation switch, or the rate of migration could contribute to abnormal cerebellar size and compartmentalization and disrupt cerebellar circuits’ wiring and function. Endocannabinoids (eCBs) have been identified as key players regulating neuron proliferation and migration in the fore- and mid-brain development, however their role in cerebellar development has not yet been explored in detail. Our preliminary results show robust expression of cannabinoid receptor 1 (CB1) in iEGL GCs, concomitant with expression diacylglycerol lipase α (DGLα) a major enzyme required for the synthesis of eCB 2-arachidonoylglycerol (2-AG), in PCs. Furthermore, our preliminary results show that cerebellar size is reduced in CB1 KOs. In this study we investigate the mechanisms through which eCB signaling may regulate GC proliferation and differentiation, focusing on the GCPs cycle length, rate of differentiation and migration.