The fission yeast cell size control system integrates pathways measuring cell surface area, volume, and time

Area of Science:

• Cell biology
• Molecular and developmental biology

Background:

• Eukaryotic cells exhibit precise size control, yet the specific size parameters (e.g., surface area, volume) governing division remain largely unelucidated.
• Fission yeast division is partly regulated by the protein kinase Cdr2, which is linked to cell surface area (SA).

Purpose of the Study:

• To investigate the mechanisms underlying cell size control in fission yeast.
• To determine whether cell division is primarily regulated by cell surface area or volume.
• To elucidate the roles of specific proteins (Cdr2, Cdc25, Cdc13) in integrating size and time cues for cell division.

Main Methods:

• Comparative analysis of cell division in wild-type and mutant fission yeast strains.
• Investigation of protein accumulation dynamics (Cdc25, Cdc13) during the cell cycle.
• Mathematical modeling and experimental validation to integrate signaling pathways.

Main Results:

• Fission yeast cells divide by surface area (SA) only below a specific size threshold.
• Mutations leading to larger cell sizes induce a shift towards volume-based division control.
• Diploid cells divide at larger sizes than haploid cells but retain SA-based division, indicating ploidy sets the threshold for switching control mechanisms.
• Cdc25 accumulation correlates with volume, while Cdc13 nuclear accumulation acts as a timer, suggesting integrated signaling.

Conclusions:

• Cell size control in fission yeast is a complex system integrating multiple inputs: cell surface area (Cdr2), cell volume (Cdc25), and cell cycle timing (Cdc13).
• This integrated system allows for flexible cell size control, exhibiting both sizer and adder properties depending on growth conditions and ploidy.
• Ploidy is a key determinant of the size threshold at which division control shifts from surface area to volume.