LAUSR

Cell migration is fundamental to proper development of the heart as well as other organs. Our characterization of a hypomorphic PIKfyve β-geo/β-geo mouse mutant, revealed that has an abnormally small heart, and raised the possibility that this could be due in part to a defect in cell migration. Moreover, a few studies suggested that PIKfyve, the sole lipid kinase that generates phosphatidylinositol 3,5-bisphosphate (PI3,5P2) and provides most of the PI5P, may have a role in migration of cultured cells. However, the localization of PIKfyve and the molecular mechanisms whereby PIKfyve regulates cell movement remain elusive. Here I show that inhibition of PIKfyve significantly impairs cell migration in cultured cell lines, as well as in primary cardiac fibroblasts, which are essential for proper heart development. Moreover, expression of a hyperactive PIKfyve mutant promotes cell migration. In order to detect the localization of endogenous PIKfyve, we used CRISPR-Cas9 genome editing to tag endogenous PIKfyve with an HA peptide at its N-terminus. Interestingly, in addition to PIKfyve localization on endosomes, a pool of PIKfyve was located at the cell leading edge. We observed PIKfyve in both lamellipodia and filopodia. Notably, we found that acute addition of PI3,5P2 or PI5P for 5 min altered filopodia dynamics. Our preliminary results suggest that PI3,5P2 and PI5P alter different properties of filopodia. These findings suggest that cell migration may be controlled in part by PI3,5P2 and PI5P which arise due to PIKfyve localization to the cell leading edge. Together, these studies suggest that mechanistic insights into how PIKfyve regulates cell migration may reveal new tools or concepts that can be utilized to study heart development in mammals.