A novel checkpoint system controlling nuclear division during Aspergillus nidulans mitotic exit.

Jonathan Davies, Colin De Souza and Stephen Osmani.

Author address: 

Department of Molecular Genetics, Ohio State University, Columbus, OH 4321


In order to generate multinucleate cells, filamentous fungi, including Aspergillus nidulans, undergo rounds of nuclear division in the absence of cytokinesis. During these closed mitoses, nuclear division must be driven by forces other than cytokinesis. In contrast, it has been suggested that cytokinesis drives nuclear division in budding yeast by promoting nuclear fission. In yeasts a dumbbell shaped nucleus can be observed during nuclear division. In contrast, we have failed to detect dumbbell shaped nuclei during mitotic exit in A. nidulans. Therefore, nuclear fission, during which constriction of the nuclear envelope generates two nuclei from one, may not occur in A. nidulans. However, nuclear division is a regulated process. For instance, dominant versions of tinD promote defective mitoses in which anaphase proceeds but, surprisingly, nuclear division does not occur. The result of this defective mitosis is an intact polyploid nucleus which can progress through further cell cycles. We propose that a regulatory mechanism exists in A. nidulans which, following detection ofmitotic defects, allows completion of DNA segregation but stops nuclear division during mitotic exit. Because mitosis is not followed by cytokinesis, the resulting nucleus is able to contribute to hyphal growth. Through the process of haploidization, normal haploid nuclei can also be subsequently generated. Thus, filamentous fungi can prevent inappropriate segregation of DNA to daughter nuclei after defective mitosis by preventing nuclear division. This survival strategy is not available to unicellular organisms, such as yeasts, because nuclear division is linked to cytokinesis

abstract No: 


Full conference title: 

23rd Fungal Genetics Conference
    • Fungal Genetics Conference 23rd (2002)