Novel types of Ca2+ release channels participate in the secretory cycle of Paramecium cells.
A database search of the Paramecium genome reveals 34 genes related to Ca(2+)-release channels of the inositol-1,4,5-trisphosphate (IP(3)) or ryanodine receptor type (IP(3)R, RyR). Phylogenetic analyses show that these Ca(2+) release channels (CRCs) can be subdivided into six groups (Paramecium tetraurelia CRC-I to CRC-VI), each one with features in part reminiscent of IP(3)Rs and RyRs. We characterize here the P. tetraurelia CRC-IV-1 gene family, whose relationship to IP(3)Rs and RyRs is restricted to their C-terminal channel domain. CRC-IV-1 channels localize to cortical Ca(2+) stores (alveolar sacs) and also to the endoplasmic reticulum. This is in contrast to a recently described true IP(3) channel, a group II member (P. tetraurelia IP(3)R(N)-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 IP(3)R(N) affects trichocyst biogenesis, while CRC-IV-1 channels are involved in signal transduction since silenced cells show an impaired release of Ca(2+) 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 Ca(2+) as signaling molecule.
Ladenburger
Eva-Maria
EM
Department of Biology, University of Constance, P.O. Box 5560, 78457 Constance, Germany. Eva.Ladenburger@uni-konstanz.de
Sehring
Ivonne M
IM
Korn
Iris
I
Plattner
Helmut
H
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D020868:Gene Silencing; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D008969:Molecular Sequence Data; D016805:Paramecium tetraurelia / Q000166:cytology / Q000378:metabolism*; D010802:Phylogeny; D015800:Protozoan Proteins / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015800:Protozoan Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium