TROPOMYOSIN ISOFORMS IN RAT NEURONS - THE DIFFERENT DEVELOPMENTAL PROFILES AND DISTRIBUTIONS OF TM-4 AND TMBR-3 ARE CONSISTENT WITH DIFFERENT FUNCTIONS

Antipeptide antisera specific for TM-4 and TMBr-3, the two tropomyosin isoforms in neurons, were used to investigate the concentrations and distributions of these F-actin-binding proteins in neurons in vitro an d in vivo. TM-4 and TMBr-3 tropomyosins had different developmental pr ofiles. TM-4 was found mainly in immature stages, while the concentrat ion of TMBr-3 increased with maturation. The two isoforms also had dif ferent subcellular distributions. TM-4 was concentrated in the growth cones of cultured neurons and, in vivo, in areas where neurites were g rowing. Later, when development was complete, TM-4 was restricted to p ostsynaptic sites in the cerebellar cortex, whereas TMBr-3 was found i n the presynaptic terminals. These data suggest that the tropomyosin i soforms have different functions, through their interaction with the a ctin cytoskeleton. TM-4 may be involved in the motile events of neurit e growth and synaptic plasticity, while TMBr-3 could play a role in st abilizing neuronal networks and synaptic functioning.