The cell wall is a structure external to the plasma membrane. Its integrity is vital and it constitutes the exoskeleton that confers mechanical strength and osmotic resistance to the fungal cell. The main structural component of the Schizosaccharomyces pombe cell wall is the β(1,3)glucan. Fission yeast contains four essential putative β(1,3)glucan synthase (GS) subunits, Bgs1 to Bgs4. Bgs1 localizes to the contractile ring and septum, and it is responsible for the synthesis of a special linear β(1,3)glucan and the primary septum that this glucan generates. Besides, Bgs1 is also localized to the growing poles. The establishment of growth polarity is controlled by a complex termed "polarisome", which is at least comprised by the marker proteins Tea1 and Tea4, the membrane protein Mod5, Bud6, the formin For3 and the GTPase Cdc42. Bgs1 depletion produces cells with bifurcated ends. We are studying the role of Bgs1 in growth polarity and we found that bgs1+ shut-off in tea1Δ or tea4Δ mutants originates spherical cells. However, this effect is not produced by bgs1+ shut-off in mod5Δ, bud6Δ or for3Δ single, double or triple mutants. This suggests that both Bgs1 and Tea proteins cooperate in an essential function for polarity establishment and maintenance. We also found that Bgs1 absence produces Mod5-GFP, actin patches and lipid-rafts delocalization all around the plasma membrane. We were able to cause actin patches delocalization by using low concentrations of the actin depolymerizing drug Latrunculin B, and observed that actin patches delocalization in tea1Δ and tea4Δ cells produces the loss of polarity. It has been described that some cdc42 thermosensitive mutants and the pob1Δ or wsp1Δ deletion mutants present delocalized actin patches around the cell periphery. Combination of these mutations with the tea1Δ and tea4Δ mutations resulted in spherical cells. These results show that Bgs1 has a role in cell polarity by controlling the actin patches localization.

Resumen del trabajo presentado a la EMBO Conference on Fission Yeast: Pombe 2013; 7th International Fission Yeast Meeting celebrada en Londres (UK) del 24 al 29 de junio de 2013.

Peer reviewed