Characterizing the Role of SEPA in Aspergillus nidulans.

Kathryn E. Sharpless, Claire L. Pearson, and Steven D. Harris.


Temperature-sensitive mutations in the sepA gene in A. nidulans cause defects in polarized morphogenesis and septation. SEPA is a member of the formin family of proteins, members of which are involved in actin microfilament organization. A previously characterized sepA disruption mutant (sepA4DBm) is able to undergo septation after a severe delay and is temperature-sensitive for growth. Another sepA disruptant has been constructed in which more of the gene, including the conserved FH1 and FH2 regions, has been deleted. This disruptant mutant, in contrast to sepA4DBm, is not temperature-sensitive for growth and fails to septate at any temperature. In addition to its defects in polarity and cytokinesis, sepA mutants have disorganized nuclei, suggesting that dynein function is compromised. Dynein, a microtubule motor, is required for proper nuclear distribution and mitotic spindle orientation in A. nidulans. We have found that mitotic spindles are misaligned in sepA mutants. Furthermore, double mutants containing a ts mutation in nudA (cytoplasmic dynein heavy chain) and compromised SEPA function (nudA2; sepA4DBm, and nudA2; alcA::sepA on glucose) display a synthetic growth defect. These findings suggest that SEPA and dynein share a similar function. To further characterize the role of SEPA in polarized growth and cytokinesis, the localization of a SEPA-GFP (green fluorescent peptide) fusion construct has been determined. SEPA-GFP localizes to the tips of growing hyphae. Additionally, SEPA-GFP localizes to a thin band coincident with septa. Localization of SEPA-GFP to septa may be cell-cycle regulated as the observation of SEPA-GFP at septa is much more rare than SEPA-GFP at the tips.

abstract No: 

Fungal Genet. Newsl. 46 (Supl):

Full conference title: 

Fungal Genetics Conference 20th
    • Fungal Genetics Conference 20th (1999)