MYOSIN FUNCTIONS IN XENOPUS RETINAL GANGLION-CELL GROWTH CONE MOTILITY IN-VIVO

The role of myosins in Xenopus retinal ganglion cell growth cone motil ity in the optic tract was studied using two pharmacologic inhibitors with different specificities. 2,3-Butanedione monoxime (BDM) disrupts myosin-actin interactions of all myosins, and ML-7 specifically inhibi ts activation of myosin II, Both inhibitors caused growth cones to ass ume a collapsed morphology and decreased growth cone speed, Similar ef fects were observed in vitro. Interestingly, the effects of the two in hibitors, while similar, were clearly distinguishable, raising the pos sibility that different myosins may have different functional roles in growth cone motility, BDM caused growth cones to withdraw lamellipodi a and some filopodia and eventually to freeze, whereas ML-7 caused tot al collapse and retraction, Concentrations of BDM and ML-7 that had no effect when applied independently stopped growth cones when applied s imultaneously, suggesting that these inhibitors act synergistically on myosin function, thus providing evidence of specificity, These result s imply that normal growth cone motility in the molecularly and spatia lly complex environment of the living brain requires myosin function. (C) 1997 John Wiley & Sons, Inc.