btn1 Affects Endocytosis, Polarization of Sterol‐Rich Membrane Domains and Polarized Growth in Schizosaccharomyces pombe

btn1, the Schizosaccharomyces pombe orthologue of the human Batten disease gene CLN3, exerts multiple cellular effects. As well as a role in vacuole pH homoeostasis, we now show that Btn1p is essential for growth at high temperatures. Its absence results in progressive defects at 37 degrees C that culminate in total depolarized growth and cell lysis. These defects are preceded by a progressive failure to correctly polarize sterol-rich domains after cytokinesis and are accompanied by loss of Myo1p localization. Furthermore, we found that in Sz. pombe, sterol spreading is linked to defective formation/polarization of F-actin patches and disruption of endocytosis and that these processes are aberrant in btn1Delta cells. Consistent with a role for Btn1p in polarized growth, Btn1p has an altered location at 37 degrees C and is retained in actin-dependent endomembrane structures near the cell poles or septum.