Researchers at the University of Geneva discovered that fungal cells block their own wall-repair mechanisms during cell fusion, making the merging process irreversible. Published in the journal Current Biology, the study on Schizosaccharomyces pombe reveals how enzyme activity coordinates wall degradation and membrane merging.
Cell fusion marks a critical moment in the sexual reproduction of many organisms. While animal cells merge without structural barriers, fungal cells feature a rigid outer boundary that protects against internal cellular pressure. To achieve successful fusion, organisms must locally degrade this protective boundary so cell membranes can join together.
A study conducted at the University of Geneva (UNIGE) and published in the journal Current Biology
investigates how cells coordinate these opposing biological imperatives. Because wall integrity is vital for survival, cells constantly monitor damage to trigger rapid repairs. The new findings explain how cells intentionally prevent their own repair systems from rebuilding the barrier at the fusion site.
The Role of Enzyme Pak2 in Yeast Fusion
To understand these fundamental cellular processes, researchers in the laboratory of Sophie Martin—a professor in the Section of Biology of the Faculty of Science at UNIGE—studied Schizosaccharomyces pombe, a single-celled yeast model. The team identified mutant yeasts lacking the enzyme Pak2 that displayed transient fusion behavior, where cells briefly connected and exchanged contents before separating again.
Normal cells accumulate the Pak2 enzyme directly at the contact zone. Its activity promotes the opening and subsequent expansion of the fusion pore, which lets cellular contents pass between the fusing cells. When Pak2 is missing, however, the process can reverse. The cells connect, trade contents, and then shut the opening.
However, when Pak2 is absent, the process can sometimes become reversible: the cells begin to fuse, exchange their contents, and then close the opening that connected them,
explained Julia Coronas-Serna, former postdoctoral researcher in Sophie Martin’s group and first author of the study.
In these cells, we observe that the mechanisms normally responsible for monitoring and repairing the cell wall become particularly active at the fusion site.
Julia Coronas-Serna, former postdoctoral researcher in Sophie Martin’s group
Rebuilding Walls After Failed Fusion Events
Using advanced imaging techniques, the research team examined the internal organization of mutant cells lacking the Pak2 enzyme at their contact interfaces. The observations revealed that once the fusion pore closes in these specific mutants, a new cell wall forms at the interface between the two cells.
Without the biological safeguards that normally block repair activity during the initial joining phase, the yeast cells can rebuild the separation they had begun to dismantle. This discovery highlights the balance cells maintain between local wall degradation and the inhibition of repair pathways.
After the fusion pore closes in these mutant cells, we observe the formation of a new cell wall at the interface between the two cells. In other words, when the mechanisms that prevent repair are absent, the cell can literally rebuild the separation it had begun to dismantle.
Sophie Martin, professor in the Section of Biology of the Faculty of Science at UNIGE
Implications for Antifungal Treatments
Uncovering the molecular controls behind cell wall dynamics offers fresh directions for antifungal strategies. The cell wall is a major target of many treatments against pathogenic fungi such as Candida
and Aspergillus
, which are responsible for infections in humans. A better understanding of the mechanisms regulating its formation and repair could ultimately help identify new molecules capable of disrupting these processes.
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