title: A novel serotonin-secreting cell type regulates ciliary motility in the mucociliary epidermis of Xenopus tadpoles.
abstract: The embryonic skin of Xenopus tadpoles serves as an experimental model system for mucociliary epithelia (MCE) such as the human airway epithelium. MCEs are characterized by the presence of mucus-secreting goblet and multiciliated cells (MCCs). A third cell type, ion-secreting cells (ISCs), is present in the larval skin as well. Synchronized beating of MCC cilia is required for directional transport of mucus. Here we describe a novel cell type in the Xenopus laevis larval epidermis, characterized by serotonin synthesis and secretion. It is termed small secretory cell (SSC). SSCs are detectable at early tadpole stages, unlike MCCs and ISCs, which are specified at early neurulation. Subcellularly, serotonin was found in large, apically localized vesicle-like structures, which were entirely shed into the surrounding medium. Pharmacological inhibition of serotonin synthesis decreased the velocity of cilia-driven fluid flow across the skin epithelium. This effect was mediated by serotonin type 3 receptor (Htr3), which was expressed in ciliated cells. Knockdown of Htr3 compromised flow velocity by reducing the ciliary motility of MCCs. SSCs thus represent a distinct and novel entity of the frog tadpole MCE, required for ciliary beating and mucus transport across the larval skin. The identification and characterization of SSCs consolidates the value of the Xenopus embryonic skin as a model system for human MCEs, which have been known for serotonin-dependent regulation of ciliary beat frequency.
authors.affiliation: University of Hohenheim, Institute of Zoology, Garbenstrasse 30, D-70593 Stuttgart, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Walentek
authors.forename: Susanne
authors.initials: S
authors.lastname: Bogusch
authors.forename: Thomas
authors.initials: T
authors.lastname: Thumberger
authors.forename: Philipp
authors.initials: P
authors.lastname: Vick
authors.forename: Eamon
authors.initials: E
authors.lastname: Dubaissi
authors.forename: Tina
authors.initials: T
authors.lastname: Beyer
authors.forename: Martin
authors.initials: M
authors.lastname: Blum
authors.forename: Axel
authors.initials: A
authors.lastname: Schweickert
mesh_terms: D000818:Animals; D002469:Cell Separation; D002923:Cilia / Q000502:physiology*; D004625:Embryo, Nonmammalian; D000078404:Epidermal Cells; D004817:Epidermis / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D007477:Ions / Q000378:metabolism; D007814:Larva; D009068:Movement / Q000502:physiology; D009093:Mucus / Q000378:metabolism; D011985:Receptors, Serotonin / Q000502:physiology; D012701:Serotonin / Q000378:metabolism*; D014981:Xenopus / Q000254:growth & development*
chemical_list: D007477:Ions; D011985:Receptors, Serotonin; D012701:Serotonin
keywords: Cilia; Mucociliary epithelium; Serotonin; Small secretory cell; Xenopus