Membrane stretching activates calcium permeability of a putative channel Pkd2 during fission yeast cytokinesis.
Pkd2 is the fission yeast homologue of polycystins. This putative ion channel localizes to the plasma membrane. It is required for the expansion of cell volume during interphase growth and cytokinesis, the last step of cell division. However, the channel activity of Pkd2 remains untested. Here, we examined the calcium permeability and mechanosensitivity of Pkd2 through in vitro reconstitution and calcium imaging of  pkd2  mutant cells. Pkd2 was translated and inserted into the lipid bilayers of giant unilamellar vesicles using a cell-free expression system. The reconstituted Pkd2 permeated calcium when the membrane was stretched via hypoosmotic shock. In vivo, inactivation of Pkd2 through a temperature-sensitive mutation  pkd2-B42  reduced the average intracellular calcium level by 34%. Compared with the wild type, the hypomorphic mutation  pkd2-81KD  reduced the amplitude of hypoosmotic shock-triggered calcium spikes by 59%. During cytokinesis, mutations of  pkd2  reduced the calcium spikes, accompanying cell separation and the ensuing membrane stretching, by 60%. We concluded that fission yeast polycystin Pkd2 allows calcium influx when activated by membrane stretching, representing a likely mechanosensitive channel that contributes to the cytokinetic calcium spikes.
Poddar A, Hsu YY, Zhang F, Shamma A, Kreais Z, Muller C, Malla M, Ray A, Liu AP, Chen Q