Proper functioning of the mammalian nervous system depends on a specific wiring pattern determined by a developmental program. This program directs how neurons divide at early stages, migrate to their final destination, outgrow cell processes and, finally, establish synapses with other neurons or a distinct target cell. A significant number of human diseases occur as a result of an aberrant completion of this developmental program. Many of these diseases, including Down's Syndrome, several forms of congenital mental retardation, phenylketonuria, malnutrition and schizophrenia are characterized by neurons with an alteration in the normal structure and number of neurites. Microtubules and microtubule-associated proteins and enzymes are known to play a crucial role in the development of normal wiring patterns in the nervous system by taking part in the extension of neuronal processes. Our laboratory is focused on the role of a specific microtubule-associated enzyme, dynamin, in the extension of neuronal processes. Dynamin is a microtubule-activated GTPase that binds and cross-links microtubules in vitro in a nucleotide-dependent manner and therefore has been proposed to act as a microtubule-based motor in vivo. We have made important preliminary observations which indicate that 1) dynamin is essential for neurite formation and 2) dynamin is localized at the neuronal growth cone. In addition, we have cloned a novel dynamin gene encoding a second isoform expressed in rat brain. From these studies, we hypothesize that dynamin contributes to the formation of neurites during development by: a) maintaining the normal structure of neuronal processes through cross-linking and positioning microtubules in the neurite and b) participating in the endocytic recycling of proteins which are important for neurite outgrowth. We have designed experiments to correlate the level of dynamin with the formation of neurites in both hippocampal neurons and PC12 cells developing in vitro. Furthermore, additional studies are aimed to alter the expression of dynamin using antisense technology and determine whether a reduced level of this protein impairs neurite outgrowth. We will use state-of-the-art video and electron microscopy in combination with molecular biological techniques to determine the integrity of the microtubule network and endocytic vesicular transport pathway in the dynamin minus neurons. To our knowledge, this is the first study which has provided insight into the in vitro role of dynamin in neuronal development. We are optimistic that a detailed characterization of the mechanisms involved in neurite formation will help us better understand many mental diseases.