G-Protein-Coupled Receptor Cell Signaling Pathways Mediating Embryonic Chick Retinal Growth Cone Collapse Induced by Lysophosphatidic Acid and Sphingosine-1-Phosphate

In the development of the nervous system, one of the critical aspects is the proper navigation of axons to their targets, i.e. the problem of axonal guidance. We used the chick visual system as a model to investigate the role of the lysophospholipids lysophosphatidic acid (LPA) and sphingosine-1-phosphate (SIP) as potential axon guidance cues. We showed that both LPA and Si P cause a specific, dose-dependent growth cone collapse of retinal neurons in vitro in the chick model system, with slight differences compared to the mouse but very similar to observations in Xenopus. Because LPA and Si P receptors are G-protein-coupled receptors, we analyzed the intracellular signaling pathways using pharmacological inhibitors in chick retinal neurons. Blocking rho kinase (ROCK) prevented growth cone collapse by LPA and S1P, while blocking PLC or chelating calcium had no effect on growth cone collapse. Inhibition of G(i/o) with pertussis toxin resulted in a partial reduction of growth cone collapse, both with LPA and with SIP. inhibition of p38 blocked growth cone collapse mediated by LPA but not Si P. Thus, in addition to the involvement of the G(12/13)-ROCK pathway, LPA- and Si P-induced collapse of chick retinal growth cones has a partial requirement for G(i/o). (C) 2014 S. Karger AG, Basel