Dbf2 is essential for cytokinesis and correct mitotic spindle formation in Candida albicans

Abstract

SummaryWe have characterized the DBF2 gene, encoding a protein kinase of the NDR family in Candida albicans, and demonstrate that this gene is essential for cell viability. Conditional mutants were constructed by using the MET3 promoter to analyse the phenotype of cells lacking this kinase. The absence of Dbf2 resulted in cells arrested as large-budded pairs that failed to contract the actomyosin ring, a function similar to that described for its Saccharomyces cerevisiae orthologue. In addition to its role in cytokinesis, Dbf2 regulates mitotic spindle organization and nuclear segregation as Dbf2-depleted cells have abnormal microtubules and severe defects in nuclear migration to the daughter cell, which results in a cell cycle block during mitosis. Taken together, these results imply that Dbf2 performs several functions during exit from mitosis and cytokinesis. Consistent with a role in spindle organization, the protein localizes to the mitotic spindle during anaphase, and it interacts physically with tubulin, as indicated by immunoprecipitation experiments. Finally, DBF2 depletion also resulted in impaired true hyphal growth.

Stk38 Modulates Rbm24 Protein Stability to Regulate Sarcomere Assembly in Cardiomyocytes

“…Stk38 has been characterized as a regulator of c-myc and p21 protein stability through phosphorylation during cell cycle progression1429. Only several reports have demonstrated changes in Stk38 expression with cytoskeleton based on genetic studies performed in fungus and flies, where its functions were involved in nuclear migration45 and normal actin dynamics4647. It remains unclear whether Stk38 kinase can also regulate the sarcomere of the heart in mammals.…”

Orthologues of the Anaphase-Promoting Complex/Cyclosome Coactivators Cdc20p and Cdh1p Are Important for Mitotic Progression and Morphogenesis in Candida albicans

“…The small proportion of cdh1⌬/cdh1⌬ cells unresponsive to serum could reflect cell-to-cell variations in the elevated levels of Clb2p, as overexpression of Clb2p or Clb4p compromises true hyphal growth (10). Consistently, other factors important for mitotic exit in C. albicans influenced hyphal growth, albeit in a stronger manner (20,28). Although a pseudohyphal state can preclude hyphal differentiation, as seen in cells lacking Gin4p, Hsl1p, and Fkh2p (11, 83), staining FIG.…”

“…The C. albicans cdh1⌬/cdh1⌬ phenotype shared more similarity with S. cerevisiae cells overexpressing CDH1 or carrying a constituitively active mutant (51,56). Thus, the results suggest that C. albicans Cdh1p has conserved and possibly novel functions, and they underscore the notion that the pathways governing mitotic progression in C. albicans involve distinct features (6,20,28). Future investigations of Cdh1p targets and regulation will provide further insights into its roles and the mitotic circuitry of the pathogen.…”

“…C. albicans has orthologues of Cdc14p phosphatase, which activates Cdh1p upon being released from the nucleolus by the Cdc14p early anaphase release (FEAR) pathway and the mitotic exit network (MEN) following degradation of Pds1p in S. cerevisiae (48,65,70,73,78), as well as the MEN kinase Dbf2p. Both factors were important for mitotic exit and cell separation but had additional novel functions and were differentially required for cell viability compared to the situation in S. cerevisiae (20,28). Cdc5p, a polo-like kinase associated with the MEN and FEAR pathways in S. cerevisiae (3), is required at earlier stages of mitosis in C. albicans, and its depletion resulted in elongated bud growth (5,6), in contrast to the large doublet morphology of cdc5 null mutants in S. cerevisiae (37).…”

Cdc28 provides a molecular link between Hsp90, morphogenesis, and cell cycle progression inCandida albicans

“…In budding yeast, cytokinesis involves the formation and contraction of an actomyosin ring, followed by septum deposition (Lippincott and Li, 1998). In C. albicans mutants with defects in cytokinesis, sometimes an actomyosin ring forms and persists through subsequent cell cycles, whereas in other cases it forms and subsequently breaks down (Li et al , 2008; Gonzalez-Novo et al , 2009). In both cases the ring is unable to contract, resulting in wider cell junctions similar to the constriction in the two-lobed daughter cell (Figures 2C and 5).…”