LOCALIZATION OF DYNAMIN - WIDESPREAD DISTRIBUTION IN MATURE NEURONS AND ASSOCIATION WITH MEMBRANOUS ORGANELLES

Tissue distribution and intracellular localization of dynamin by immun oblotting and immunocytochemistry is investigated in this study. Dynam in was widely expressed in all the neurons we examined, and was especi ally abundant in the central nervous system after maturation, although its expression presented regional heterogeneity. Dynamin was present most abundantly in cerebellar Purkinje cells and hippocampal pyramidal cells, and to a lesser extent in motor neurons and peripheral nerves. However, dynamin was nearly absent in cells such as anterior pituitar y cells and adrenal medullary cells which secrete mainly dense-cored v esicles. Dynamin was localized not only in cell bodies, axons, and syn apses but also in dendrites. Subcellular fractionation indicated that dynamin existed in the membrane fraction as well as in the soluble fra ction. In ligated peripheral nerves, dynamin colocalized with tubulove sicular membranous organelles transported mainly anterogradely. By tra nsfection of dynamin cDNA into mouse fibroblast L-cells, we showed it colocalized with some membranous organelles but not with microtubules. Our results show that dynamin is associated with membranous organelle s in vivo, although a certain amount of dynamin also exists in the sol uble fraction and is distributed diffusely throughout mature neurons. The data suggest that dynamin's fundamental role involves membrane tra fficking in neurons in the central nervous system rather than in slidi ng microtubules as a motor protein.