The Aspergillus nidulans sepA gene encodes an FH1/2 protein involved in cytokinesis and the maintenance of cellular polarity

The duplication cycle in Aspergillus nidulans

The duplication cycle encompasses the spectrum of events required for the growth and division of individual cells within a fungal hyphae. Recent advances in understanding the mechanisms which underlie nuclear division and cellular morphogenesis in the filamentous fungus Aspergillus nidulans have shown that in many respects, the duplication cycle differs significantly from the cell cycles of both budding and fission yeast. The purpose of this review is to summarize these advances and to highlight the fundamental differences between the duplication cycle and the yeast cell cycles. In addition, it is argued that the duplication cycle is controlled by cellular regulatory networks which integrate the processes of nuclear division, cellular morphogenesis, and cell growth with each other. Functional dissection of these networks should help to reveal features that are unique to the hyphal mode of growth.

cdc12p, a protein required for cytokinesis in fission yeast, is a component of the cell division ring and interacts with profilin

As in many other eukaryotic cells, cell division in fission yeast depends on the assembly of an actin ring that circumscribes the middle of the cell. Schizosaccharomyces pombe cdc12 is an essential gene necessary for actin ring assembly and septum formation. Here we show that cdc12p is a member of a family of proteins including Drosophila diaphanous, Saccharomyces cerevisiae BNI1, and S. pombe fus1, which are involved in cytokinesis or other actin-mediated processes. Using indirect immunofluorescence, we show that cdc12p is located in the cell division ring and not in other actin structures. When overexpressed, cdc12p is located at a medial spot in interphase that anticipates the future ring site. cdc12p localization is altered in actin ring mutants. cdc8 (tropomyosin homologue), cdc3 (profilin homologue), and cdc15 mutants exhibit no specific cdc12p staining during mitosis. cdc4 mutant cells exhibit a medial cortical cdc12p spot in place of a ring. mid1 mutant cells generally exhibit a cdc12p spot with a single cdc12p strand extending in a random direction. Based on these patterns, we present a model in which ring assembly originates from a single point on the cortex and in which a molecular pathway for the functions of cytokinesis proteins is suggested. Finally, we found that cdc12 and cdc3 mutants show a synthetic-lethal genetic interaction, and a proline-rich domain of cdc12p binds directly to profilin cdc3p in vitro, suggesting that one function of cdc12p in ring assembly is to bind profilin.