A Novel Role for Polycystin-2 (Pkd2) in <i>P. tetraurelia</i> as a Probable Mg²⁺ Channel Necessary for Mg²⁺-Induced Behavior

• Main Authors: Megan S. Valentine, Junji Yano, Judith Van Houten
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Genes
• Subjects: Polycystin-2; channelopathy; cilia; cell body membrane; magnesium channel; electrophysiology; behavior; over-expression; trafficking
• Online Access: https://www.mdpi.com/2073-4425/10/6/455
• ISSN: 2073-4425

A human ciliopathy gene codes for Polycystin-2 (Pkd2), a non-selective cation channel. Here, the Pkd2 channel was explored in the ciliate <i>Paramecium tetraurelia</i> 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 <i>eccentric</i> (XntA1), a <i>Paramecium</i> mutant lacking the inward Ca²⁺-dependent Mg²⁺ 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 Mg²⁺ solutions, respectively. Over-expression of Pkd2-FLAG in the XntA1 mutant caused slower swimming, supporting an increase in Mg²⁺ permeability, in agreement with the electrophysiology data. We propose that Pkd2 in <i>P. tetraurelia</i> collaborates with XntA for Mg²⁺-induced behavior. Our data suggest Pkd2 is sufficient and necessary for Mg²⁺ conductance and membrane permeability to Mg²⁺, and that Pkd2 is potentially a Mg²⁺-permeable channel.