Cannabinoid receptor type 1 regulates sequential stages of migration and morphogenesis of neural crest cells and derivatives in chicken and frog embryos

The main cannabinoid receptor CB1R first shows expression during early neurula stage in chicken (Gallus gallus) embryos, and at early tailbud stage in the frog (Xenopus laevis) embryos. This raises the question of whether CB1R regulates similar or distinct processes during the embryonic development of these two species. Here, we examined whether CB1R influences the migration and morphogenesis of neural crest cells and derivatives in both chicken and frog embryos. Early neurula stage chicken embryos were exposed to arachidonyl‐2ʹ‐chloroethylamide (ACEA; a CB1R agonist), N‐(Piperidin‐1‐yl)‐5‐(4‐iodophenyl)‐1‐(2,4‐dichlorophenyl)‐4‐methyl‐1H‐pyrazole‐3‐carboxamide (AM251; a CB1R inverse agonist) or Blebbistatin (nonmuscle Myosin II inhibitor) in ovo and examined during migration of neural crest cells and at condensing cranial ganglia stage. Early tailbud stage frog embryos were bathed in ACEA, AM251 or Blebbistatin, and analyzed at late tailbud stage for changes in craniofacial and eye morphogenesis, and in patterning and morphology of melanophores (neural crest‐derived pigment cells). In chicken embryos exposed to ACEA and Myosin II inhibitor, cranial neural crest cells migrated erratically from the neural tube, and the right, but not the left, ophthalmic nerve of the trigeminal ganglia was affected in ACEA‐ and AM251‐treated embryos. In frog embryos with inactivation or activation of CB1R, or inhibition of Myosin II, the craniofacial and eye regions were smaller and/or less developed, and the melanophores overlying the posterior midbrain were more dense, and stellate in morphology, than the same tissues and cells in control embryos. This data suggests that despite differences in the time of onset of expression, normal activity of CB1R is required for sequential steps in migration and morphogenesis of neural crest cells and derivatives in both chicken and frog embryos. In addition, CB1R may signal through Myosin II to regulate migration and morphogenesis of neural crest cells and derivatives in chicken and frog embryos.