SUBCELLULAR-LOCALIZATION OF MYOSIN-V IN NERVE GROWTH CONES AND OUTGROWTH FROM DILUTE-LETHAL NEURONS

Myosin V-null mice (dilute-lethal mutants) exhibit apparent neurologic al defects that worsen from birth until death in the third postnatal w eek, Although myosin V is enriched in brain, the neuronal function of myosin V is unclear and the underlying cause of the neurological defec ts in these mice is unknown, To aide in understanding myosin V functio n, we examined the distribution of myosin V in the rodent superior cer vical ganglion (SCG) growth cone, a well characterized neuronal struct ure in which myosin V is concentrated, Using affinity purified, myosin V-specific antibodies in immunofluorescence and immunoelectron micros copy, we observed that myosin V is concentrated in organelle-rich regi ons of the growth cone, Myosin V is present on a distinct population o f small (50-100 nm) organelles, and on actin filaments and the plasma membrane, Myosin V-associated organelles are present on both microtubu les and actin filaments, These results indicate that myosin V may be c arried as a passenger on organelles that are transported along microtu bules, and that these organelles may also be capable of movement along actin filaments, In addition, we found no abnormalities in outgrowth, morphology, or cytoskeletal organization of SCG growth cones from dil ute-lethal mice, These results indicate that myosin V is not necessary for the traction force needed for growth cone locomotion, for organiz ation of the actin cytoskeleton, or for filopodial dynamics.