A Novel Role for Polycystin-2 (Pkd2) in P. tetraurelia as a Probable Mg 2+ Channel Necessary for Mg 2+ -Induced Behavior

摘要

A human ciliopathy gene codes for Polycystin-2 (Pkd2), a non-selective cation channel. Here, the Pkd2 channel was explored in the ciliate Paramecium tetraurelia using combinations of RNA interference, over-expression, and epitope-tagging, in a search for function and novel interacting partners. Upon depletion of Pkd2, cells exhibited a phenotype similar to eccentric (XntA1), a Paramecium mutant lacking the inward Ca 2+ -dependent Mg 2+ conductance. Further investigation showed both Pkd2 and XntA localize to the cilia and cell membrane, but do not require one another for trafficking. The XntA-myc protein co-immunoprecipitates Pkd2-FLAG, but not vice versa, suggesting two populations of Pkd2-FLAG, one of which interacts with XntA. Electrophysiology data showed that depletion and over-expression of Pkd2 led to smaller and larger depolarizations in Mg 2+ solutions, respectively. Over-expression of Pkd2-FLAG in the XntA1 mutant caused slower swimming, supporting an increase in Mg 2+ permeability, in agreement with the electrophysiology data. We propose that Pkd2 in P. tetraurelia collaborates with XntA for Mg 2+ -induced behavior. Our data suggest Pkd2 is sufficient and necessary for Mg 2+ conductance and membrane permeability to Mg 2+ , and that Pkd2 is potentially a Mg 2+ -permeable channel.