Signalling mechanisms driving cell guidance in a physiological electric field
Endogenous electric fields (EFs) are present during development and regeneration. Enhancing the endogenous EFs during regeneration augments healing and blocking them attenuates it. Two well-characterised electrotropic systems, cultures of Xenopus spinal neurones and cultures of bovine corneal epithelial cells (CECs), were used to explore the molecular signalling cascades that underlie directed migration in an EF. Most growth cones of cultured Xenopus neurons and most CECs migrate towards the cathode. Directional migration of CECs on a grooved substratum was also investigated. The results indicate that: - Cathodal growth cone turning requires rac and cdc42 activity, and modulation of microfilaments. Blocking the rac and cdc42 CRIB domains or application of latrunculin A disrupted filopodia/lamellipodia and abolished cathodal turning. - The rhoA-rho-kinase-myosin cascade is required only transiently in cathodal growth cone turning. - Neither ERK1/2 no p38 MAPK were required for cathodal growth cone turning. - Cathodal CEC migration is dependent upon cdc42 but not rac. Blocking the cdc42 CRIB domain abolished CEC cathodal migration and cathodal re-distribution of lamellipodia. Blocking the rac CRIB domain reduced the number of cells with lamellipodia and lamellipodial area, but did not affect cathodal migration. - CEC migration along the grooves was not affected by any of the treatments tested. - Upon orthogonal presentation of an EF and grooves, rhoA activity influenced the CEC response. Normally grooves provided the more potent guidance cue but when rhoA activity was attenuated the EF dominated. Understanding the signalling pathways underlying these guidance cues will help to optimise future therapies directed at CNS regeneration and wound healing.