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Molecular and Cellular Biology, July 2009, p. 3605-3622, Vol. 29, No. 13
0270-7306/09/$08.00+0     doi:10.1128/MCB.01592-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Novel Types of Ca2+ Release Channels Participate in the Secretory Cycle of Paramecium Cells{triangledown} ,{dagger}

Eva-Maria Ladenburger,* Ivonne M. Sehring, Iris Korn, and Helmut Plattner

Department of Biology, University of Constance, 78457 Constance, Germany

Received 10 October 2008/ Returned for modification 20 November 2008/ Accepted 14 April 2009

A database search of the Paramecium genome reveals 34 genes related to Ca2+-release channels of the inositol-1,4,5-trisphosphate (IP3) or ryanodine receptor type (IP3R, RyR). Phylogenetic analyses show that these Ca2+ release channels (CRCs) can be subdivided into six groups (Paramecium tetraurelia CRC-I to CRC-VI), each one with features in part reminiscent of IP3Rs and RyRs. We characterize here the P. tetraurelia CRC-IV-1 gene family, whose relationship to IP3Rs and RyRs is restricted to their C-terminal channel domain. CRC-IV-1 channels localize to cortical Ca2+ stores (alveolar sacs) and also to the endoplasmic reticulum. This is in contrast to a recently described true IP3 channel, a group II member (P. tetraurelia IP3RN-1), found associated with the contractile vacuole system. Silencing of either one of these CRCs results in reduced exocytosis of dense core vesicles (trichocysts), although for different reasons. Knockdown of P. tetraurelia IP3RN affects trichocyst biogenesis, while CRC-IV-1 channels are involved in signal transduction since silenced cells show an impaired release of Ca2+ from cortical stores in response to exocytotic stimuli. Our discovery of a range of CRCs in Paramecium indicates that protozoans already have evolved multiple ways for the use of Ca2+ as signaling molecule.

* Corresponding author. Mailing address: Department of Biology, University of Constance, P.O. Box 5560, 78457 Constance, Germany. Phone: 49-7531-884230. Fax: 49-7531-882245. E-mail: Eva.Ladenburger{at}uni-konstanz.de

{triangledown} Published ahead of print on 20 April 2009.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

Molecular and Cellular Biology, July 2009, p. 3605-3622, Vol. 29, No. 13
0270-7306/09/$08.00+0     doi:10.1128/MCB.01592-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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