title: Molecular Factors of Nematocyst Morphogenesis and Discharge in the Freshwater Polyp Hydra
creator: Beckmann, Anna
subject: 500
subject: 500 Natural sciences and mathematics
subject: 570
subject: 570 Life sciences
description: Stinging cells or nematocytes are specialized cells that are unique to Cnidarians. They contain a highly sophisticated organelle, the nematocyst, used for locomotion, defence and capture of prey. The proteome of the nematocyst has provided unique insights into its molecular organisation. The goal of my thesis was to investigate novel molecular factors involved in aspects of nematocyst morphogenesis, structure and function.  A critical part of nematocyst morphogenesis is the initiation of tubule formation by a constriction of the Golgi vesicle membrane. Nematomyosin, a newly identified non-muscle myosin type II, in the present thesis is shown to localize to a collar around the outgrowing tubule indicating an essential role in this process. Blocking of myosin II activity by Blebbistatin leads to malformed nematocyst vesicles. Tubule size control is probably facilitated by a PKD2 channel, shown to be active at the point of maximal tubule outgrowth.  The nematocyst structure has been characterized by stiff and tear-resistant minicollagens, although the discharge process is accompanied by extreme volume changes of the capsule. Here, I have characterized the novel elastic protein Cnidoin that shares structural homology with the spider silk protein Spidroin-2. Cnidoin is expressed in developing nematocytes and locates to wall and tubule structures. Recombinant Cnidoin showed a high tendency to aggregate and to form linear fibres. Cnidoin thus behaves as a typical elastic protein. Being an integral part of the mature nematocyst it could provide the molecular basis for the energy stored that is released in the ultrafast discharge process.  The discharge of nematocysts is triggered by chemical and mechanical stimuli that are detected by the cnidocil at the apical end of the nematocyte. The cnidocil is surrounded by a set of stereocilia, providing a similar arrangement as vertebrate hair cells. A newly identified calcium channel of the TrpA family is shown to locate to stereocilia of the Hydra cnidocil apparatus. The protein can be visualized by immunostainings during developmental stages as well as in mature capsules and thus represents a candidate for mechanosensation during discharge. Nematocalcin, a penta-EF-hand protein, was also located to the stereocilia, but at a more basal position than TrpA, where it might act as a modulatory factor associated with the mechanosensory apparatus.
date: 2013
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/15956/1/Beckmann%20Dissertation.pdf
identifier: DOI:10.11588/heidok.00015956
identifier: urn:nbn:de:bsz:16-heidok-159565
identifier:   Beckmann, Anna  (2013) Molecular Factors of Nematocyst Morphogenesis and Discharge in the Freshwater Polyp Hydra.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/15956/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng