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

Abstract

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 378C 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 btn1D cells. Consistent with a role for Btn1p in polarized growth, Btn1p has an altered location at 378C and is retained in actin-dependent endomembrane structures near the cell poles or septum.

Ste20-kinase-dependent TEDS-site phosphorylation modulates the dynamic localisation and endocytic function of the fission yeast class I myosin, Myo1

“…In addition to the defects in polarised growth and F-actin patch polarisation brought about by deletion of myo1 + , deletion of both budding yeast myosin genes also results in defects in fluid-phase endocytosis (Codlin et al, 2008;Geli and Riezman, 1996;Lee et al, 2000). This is consistent with recent work that has shown the formation and polymerisation of cortical F-actin patches to be intimately linked to the process of endocytosis (Kaksonen et al, 2006).…”

“…We next determined whether Myo1 Ser361 phosphorylation played a role in regulating Myo1 function during endocytosis (Codlin et al, 2008). To confirm the role of Myo1 during endocytosis, the uptake of the lyphophylic dye FM4-64 was monitored in myo1 + , myo1⌬ myo1-S361A and myo1-S361D cells, and FM4-64 internalisation from the moment of its addition to the cells.…”

The recruitment of acetylated and unacetylated tropomyosin to distinct actin polymers permits the discrete regulation of specific myosins in fission yeast

“…The fission yeast class I myosin, Myo1, localises to dynamic foci at sites of cell growth, from which they seed the polymerisation of Arp2/3-dependent actin patches and promote endocytosis (Attanapola et al, 2009;Codlin et al, 2008;Lee et al, 2000). As these actin structures lack Cdc8 it was unsurprising that lack of Tm acetylation had no significant affect upon the cellular distribution of this motor protein, which continued to be recruited to foci at sites of growth in naa25 cells (Fig.…”

Regulation and function of the fission yeast myosins

“…This Myo1 function is reflected in the phenotype of myo1⌬ cells, which lack a polarised distribution of cortical actin patches as well as a polarised pattern of cell growth. Similarly, Myo1 associates with actin patches (Lee et al, 2000;Sirotkin et al, 2005;Toya et al, 2001), where it not only promotes actin polymerisation but also plays a key role in membrane remodelling and endocytosis (Attanapola et al, 2009;Codlin et al, 2008). Its association with the membrane is highly dynamic; each interaction lasts ~14 seconds.…”

“…As in all class I myosins, the tail of Myo1 contains a conserved tail homology domain (TH1 domain), which is required for the association of Myo1 with dynamic lipid regions. The TH1 domain thus permits Myo1-dependent deformation of cellular membranes during endocytosis and, probably, specialised membrane reorganisation during meiosis (Codlin et al, 2008;Itadani et al, 2006;Lee et al, 2000;Takeda and Chang, 2005;Toya et al, 2001).…”