The cortical ER network limits the permissive zone for actomyosin ring assembly.

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Accurate cell division requires precise positioning of the division plane for proper genetic segregation and daughter cell fate determination.
• The cortical endoplasmic reticulum (ER) forms a network of tubules and cisternae, stabilized by proteins like reticulon and DP1, influencing cell shape and potentially other functions.

Purpose of the Study:

• To investigate the role of the cortical endoplasmic reticulum (ER) network in regulating cell division site positioning in the fission yeast Schizosaccharomyces pombe.
• To identify the key proteins responsible for maintaining the cortical ER network and their impact on cell division.

Main Methods:

• Genetic analysis of fission yeast strains lacking specific ER-associated proteins (Rtn1p, Yop1p, Tts1p).
• Microscopy to observe the organization of the cortical ER network and the localization of the division site regulator Mid1p.
• Analysis of actomyosin cable assembly and ring formation in mutant cells.

Main Results:

• The ER network in Schizosaccharomyces pombe is maintained by Rtn1p, Yop1p, and the newly identified Tts1p.
• Cells lacking this ER network exhibit severe defects in division plane positioning.
• These defects arise from the aberrant dispersion of Mid1p along the cell cortex, leading to disorganized actomyosin ring assembly.

Conclusions:

• The cortical ER network acts as a scaffold, restricting the lateral movement of Mid1p.
• This restriction creates a defined zone at the cell equator, ensuring proper actomyosin ring assembly and accurate cell division.
• The study reveals a novel link between ER organization and cell division site selection.