Regulation of cytokinesis in the milk yeast Kluyveromyces lactis

Abstract

Cytokinesis in yeast and mammalian cells is a highly coordinated process mediated by the constriction of an actomyosin ring. In yeasts, it is accompanied by the formation of a chitinous primary septum. Although much is known about the regulation of cytokinesis in budding yeast, overlapping functions of redundant genes complicates genetic analyses. Here, we investigated the effects of various deletion mutants on cytokinesis in the milk yeast Kluyveromyces lactis. To determine the spatiotemporal parameters of cytokinesis components, live-cell imaging of fluorophor-tagged KlMyo1 and a new Lifeact probe for KlAct1 was employed. In contrast to Saccharomyces cerevisiae, where deletion of ScMYO1 is lethal, Klmyo1 deletion was temperature-sensitive. Transmission and scanning electron microscopy demonstrated that the Klmyo1 deletion cells had a defect in the formation of the primary septum and in cell separation; this result was confirmed by FACS analyses. Deletion of KlCYK3 was lethal, whereas in S. cerevisiae a cyk3 deletion is synthetically lethal with hof1 deletion. Growth of Klhof1 mutants was osmoremedial at 25°C, as it is in S. cerevisiae. CYK3 and HOF1 genes cross-complemented in both species, suggesting that they are functional homologs. Inn1, a common interactor for these two regulators, was essential in both yeasts and the encoding genes did not cross-complement. The C2 domain of the Inn1 homologs conferred species specificity. Thus, our work establishes K. lactis as a model yeast to study cytokinesis with less genetic redundancy than S. cerevisiae. The viability of Klmyo1 deletions provides an advantage over budding yeast to study actomyosin-independent cytokinesis. Moreover, the lethality of Klcyk3 null mutants suggests that there are fewer functional redundancies with KlHof1 in K. lactis.