A molecular genetic analysis of septation in Aspergillus nidulans
Abstract
The filamentous fungus A. nidulans partitions cells by septum formation. The process of septum formation is analogous to cytokinesis in animal cells. A screen for temperature-sensitive mutants of A. nidulans defective in septum formation identified five new genes (sepE, G, H, I and J). Three additional septation genes (sepA, B, and D) had been identified in a previous screen for ts mutants (Morris, N. R. 1976. Genet. Res. Camb. 26:237-254). These eight genes were grouped into classes based on analysis of mutant phenotypes. Relationships among the sep gene products were also investigated through double mutant analysis. The Class I mutants (sepB3, sepE1, sep-I1, and sepJ1) display an aberrant nuclear morphology in addition to the inability to form septa, suggesting that these gene products are involved in the regulation of septation. Mutations in the sepB and sepJ genes result in defects which appear to activate a checkpoint which delays cell cycle progression into cytokinesis (Harris and Hamer, 1996. EMBO J. 14:5244-5257; this study). The sepE1 and sepI1 mutants also display cell wall defects, indicating a possible role for these gene products in cell wall synthesis or in regulation of the actin cytoskeleton which plays a role in directing cell wall growth. Mutations in the Class II sepA gene result in polarity defects, including extensive branching and wide hypha, suggesting a role in actin organization. The Class III mutants (sepD5, sepG1, and sepH1) are unable to form septa although growth and nuclear division continue. Double mutant analysis indicates that these gene products are required late in the process of septum formation. Synthetic lethal interactions were observed in the crosses among the sepE1, sepI1 and sepH1 mutants, suggesting that these gene products may interact. The sepH gene has been cloned and encodes a protein kinase which shows significant similarity to the Cdc7 kinase of S. pombe which is also required for septum formation (Fankhauser and Simanis, 1994. EMBO J. 13:3011-3019). The sepH1 mutant is able to form actin rings but fails to form a division septum, suggesting that the SepH kinase may be required to promote the final stages of cytokinesis and septum formation.
Degree
Ph.D.
Advisors
Hamer, Purdue University.
Subject Area
Genetics|Molecular biology
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