{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,15]],"date-time":"2026-01-15T00:20:44Z","timestamp":1768436444765,"version":"3.49.0"},"reference-count":46,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2025,10,16]],"date-time":"2025-10-16T00:00:00Z","timestamp":1760572800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency"},{"name":"Daiichi Sankyo Science Foundation"},{"DOI":"10.13039\/100020236","name":"Japan Foundation for Pediatric Research","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100020236","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Mishima Kaiun Memorial Foundation"},{"name":"Otsuka Science Foundation"},{"DOI":"10.13039\/100007449","name":"Takeda Science Foundation","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100007449","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Genetic truncation or mutation of the gene encoding band 4.1, ezrin, radixin, and moesin (FERM) domain protein containing 4A (FRMD4A) is associated with brain developmental diseases, including microcephaly with global developmental delay. It has also been identified as a risk factor for Alzheimer\u2019s disease. By analogy with other FERM domain-containing proteins, FRMD4A is believed to regulate cell morphogenesis and\/or cell polarization in central nervous system (CNS) cells; however, it remains unclear whether and how dysfunction of FRMD4A and\/or its closely homologous protein FRMD4B causes abnormal morphogenesis in neuronal cells. Here, we describe for the first time the roles of FRMD4A and FRMD4B in process elongation in neuronal cells. Knockdown of Frmd4a or Frmd4b using specific RNA-targeting clustered regularly interspaced short palindromic repeat (CRISPR) and Cas13-fitted gRNAs led to decreased process elongation in primary cortical neurons. Similar decreases in neuronal marker expression were observed in the N1E-115 cell line, a model of neuronal differentiation. Furthermore, hesperetin, an aglycone of the citrus flavonoid hesperidin known to promote neuroprotective signaling, recovered the decreased process elongation induced by the knockdown of Frmd4a or Frm4b. Hesperetin also stimulated phosphorylation of mitogen-activated protein kinases\/extracellular signal-regulated kinases (MAPKs\/ERKs), which could help promote neuronal processes. These results suggest that FRMD4A and FRMD4B regulate process elongation through a possible signaling pathway linked to the sustained phosphorylation of MAPKs\/ERKs. Crucially, this study reveals that, at the molecular and cellular levels, hesperetin can restore normal phenotypes when FRMD4A protein or FRMD4B protein is impaired.<\/jats:p>","DOI":"10.3390\/ijms262010083","type":"journal-article","created":{"date-parts":[[2025,10,16]],"date-time":"2025-10-16T12:17:02Z","timestamp":1760617022000},"page":"10083","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Knocking Down FRMD4A, a Factor Associated with the Brain Development Disorder and a Risk Factor for Alzheimer\u2019s Disease, Using RNA-Targeting CRISPR\/Cas13 Reveals Its Role in Cell Morphogenesis"],"prefix":"10.3390","volume":"26","author":[{"given":"Asahi","family":"Honjo","sequence":"first","affiliation":[{"name":"Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0982, Tokyo, Japan"},{"name":"Laboratory for Drug Target Discovery, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0392, Tokyo, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2632-8488","authenticated-orcid":false,"given":"Hideji","family":"Yako","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0982, Tokyo, Japan"},{"name":"Laboratory for Drug Target Discovery, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0392, Tokyo, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9298-5799","authenticated-orcid":false,"given":"Yuki","family":"Miyamoto","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0982, Tokyo, Japan"},{"name":"Laboratory for Drug Target Discovery, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0392, Tokyo, Japan"},{"name":"Department of Pharmacology, National Research Institute for Child Health and Development, Okura, Setagaya 157-8535, Tokyo, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Moeri","family":"Yagi","sequence":"additional","affiliation":[{"name":"TSUMURA\u00a0 Advanced Technology Research Laboratories, TSUMURA & CO., Ami, Inashiki 300-1192, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Masahiro","family":"Yamamoto","sequence":"additional","affiliation":[{"name":"TSUMURA\u00a0 Advanced Technology Research Laboratories, TSUMURA & CO., Ami, Inashiki 300-1192, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0495-3023","authenticated-orcid":false,"given":"Akinori","family":"Nishi","sequence":"additional","affiliation":[{"name":"TSUMURA\u00a0 Advanced Technology Research Laboratories, TSUMURA & CO., Ami, Inashiki 300-1192, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hiroyuki","family":"Sakagami","sequence":"additional","affiliation":[{"name":"Department of Anatomy, Kitasato University School of Medicine, Minami, Sagamihara 252-0374, Kanagawa, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3618-998X","authenticated-orcid":false,"given":"Junji","family":"Yamauchi","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0982, Tokyo, Japan"},{"name":"Laboratory for Drug Target Discovery, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji 192-0392, Tokyo, Japan"},{"name":"Department of Biological Science, Tokyo College of Biotechnology, Kitakojiya, Ota 144-0032, Tokyo, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,10,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"905","DOI":"10.1073\/pnas.65.4.905","article-title":"Surface movements during the growth of single explanted neurons","volume":"65","author":"Bray","year":"1970","journal-title":"Proc. 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