title: Apical secretion in epithelial tubes of the Drosophila embryo is directed by the Formin-family protein Diaphanous.
abstract: Apical localization of filamentous actin (F-actin) is a common feature of epithelial tubes in multicellular organisms. However, its origins and function are not known. We demonstrate that the Diaphanous (Dia)/Formin actin-nucleating factor is required for generation of apical F-actin in diverse types of epithelial tubes in the Drosophila embryo. Dia itself is apically localized both at the RNA and protein levels, and apical localization of its activators, including Rho1 and two guanine exchange factor proteins (Rho-GEFs), contributes to its activity. In the absence of apical actin polymerization, apical-basal polarity and microtubule organization of tubular epithelial cells remain intact; however, secretion through the apical surface to the lumen of tubular organs is blocked. Apical secretion also requires the Myosin V (MyoV) motor, implying that secretory vesicles are targeted to the apical membrane by MyoV-based transport, along polarized actin filaments nucleated by Dia. This mechanism allows efficient utilization of the entire apical membrane for secretion.
authors.affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: R'ada
authors.initials: R
authors.lastname: Massarwa
authors.forename: Eyal D
authors.initials: ED
authors.lastname: Schejter
authors.forename: Ben-Zion
authors.initials: BZ
authors.lastname: Shilo
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D016764:Cell Polarity; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000196:embryology* / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology* / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism*; D000080865:Formins; D018507:Gene Expression Regulation, Developmental; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D024701:Myosin Type V / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors; D022142:Secretory Vesicles / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D000080865:Formins; D020662:Guanine Nucleotide Exchange Factors; D008840:Microfilament Proteins; D012333:RNA, Messenger; D064067:Rho Guanine Nucleotide Exchange Factors; C106890:diaphanous protein, Drosophila; D024701:Myosin Type V; C511153:Rho1 protein, Drosophila; D020741:rho GTP-Binding Proteins