Axonal transport of actin in rabbit retinal ganglion cells.

Abstract

Proteins in the cell bodies of rabbit retinal ganglion cells were labeled with [35S]methionine and the appearance of radioactive actin in tissues containing the axons and synaptic terminals of these neurons, i.e., the optic nerve (ON), optic tract (OT), lateral geniculate nucleus (LGN) and the superior colliculus (SC) was observed. The temporal sequence of appearance of labeled actin (which was identified by its specific binding to DNase I, its electrophoretic mobility and its peptide map) in these tissues indicated that actin is an axonally transported protein with a maximum transport velocity of 3.4-4.3 mm/day. The kinteics of labeling actin were similar to the kinetics of labeling 2 proteins (M1 and M2) which resemble myosin; these myosin-like proteins were previously found to be included in the groups of proteins (groups III and IV) transported with the 3rd and 4th most rapid maximum velocities. The similarity in transport between actin and myosin-like proteins supports the idea that a number of proteins in the 3rd and 4th transport groups may be functionally related by virtue of their involvement in a force-generating mechanism and suggests the possibility that these proteins may be axonally transported as a preformed force-generating unit.