Summer Research Description: Filopodia are thin, headless, actin rich protrusions that are precursors of dendritic spines in neurons. Dendritic spines are actin rich postsynaptic protrusions that receive mostly glutamergic excitatory inputs. Alterations in the number and morphology of spines have been associated with many behavioral and memory-related disorders. Exosomes are 40-100nm sized extracellular vesicles of endocytic origin with functions implicated in cellular communication. Of interest are Hrs and Rab27b, proteins that regulate exosome biogenesis and secretion, respectively. We hypothesize that exosome are important for the formation of filopodia and spines. Preliminary results from Dr. Webb’s lab indicate that Rab27b localizes to the tips and bases of filopodia and spines in primary rat hippocampal neurons. Also, GFP-Rab27b expression leads to an increase in number of filopodia and spines, while Rab27/Hrs knockdown causes a decrease in filopodia and spine density. Next we will examine these effects of Rab27b expression and Rab27b/Hrs knockdown in primary rat cortical neurons. We will also perform knockdown of Rab27b/Hrs and examine changes in exosome secretion to further confirm that the effects are due to change in exosome secretion. Furthermore, we will add purified exosomes to Rab27b/Hrs knockdown neurons to rescue the phenotype.