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In neurons, fascin has been thought to primarily function in axons, as previous studies reported its absence from dendritic filopodia and spines. Here, we demonstrate that fascin is both present and functionally important in dendritic compartments. Using optimized immunocytochemistry and CRISPR-based endogenous tagging of fascin1 in cultured hippocampal neurons, we show that fascin is concentrated in developing dendritic filopodia and enriched in mature dendritic spines. Super- resolution imaging further reveals that fascin is organized into discrete nanoscale foci within spine heads, but not the spine neck. Finally, we show that CRISPR-mediated knockout of fascin1 in mature hippocampal neurons impairs synaptic potentiation, without affecting baseline excitatory synaptic transmission. Together, our findings uncover a previously overlooked aspect of actin organization in dendritic spines and establish fascin as a critical regulator of postsynaptic plasticity.<\/jats:p>\n                <jats:sec>\n                  <jats:title>Summary Statement<\/jats:title>\n                  <jats:p>The actin bundling protein fascin localizes to dendritic filopodia and spines, where it regulates activity-dependent synaptic plasticity.<\/jats:p>\n                <\/jats:sec>","DOI":"10.1101\/2025.10.03.680376","type":"posted-content","created":{"date-parts":[[2025,10,4]],"date-time":"2025-10-04T18:00:13Z","timestamp":1759600813000},"source":"Crossref","is-referenced-by-count":0,"title":["Fascin in Dendritic Protrusions is Required for Synaptic Plasticity"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8093-422X","authenticated-orcid":false,"given":"James Q","family":"Zheng","sequence":"first","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"},{"name":"Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322"},{"name":"Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shuristeen","family":"Joubert","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Carlos","family":"Gonzalez-Islas","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuki","family":"Ogawa","sequence":"additional","affiliation":[{"name":"Department of Biological Sciences, McCausland College of Arts and Sciences, University of South Carolina, Columbia, SC 29208"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Abhishek","family":"Poddar","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Arjolyn B","family":"Penas","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Enyu","family":"Liu","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter","family":"Wenner","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kenneth R","family":"Myers","sequence":"additional","affiliation":[{"name":"Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026082014252843000_2025.10.03.680376v3.1","doi-asserted-by":"crossref","unstructured":"Malenka, R. 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