Cortical actin contributes to spatial organization of ER-PM junctions

Area of Science:

• Cell Biology
• Molecular Biology

Background:

• Endoplasmic reticulum-plasma membrane (ER-PM) junctions are critical sites for cellular processes like calcium (Ca2+) signaling and lipid metabolism.
• The spatial organization and morphology of ER-PM junctions are not well understood, limiting our comprehension of their functional regulation.

Purpose of the Study:

• To characterize the morphology and spatial distribution of ER-PM junctions.
• To investigate the role of the actin cytoskeleton in regulating ER-PM junction organization and function.

Main Methods:

• Photoactivated localization microscopy (PALM) was employed to determine the dimensions of individual ER-PM junctions.
• Total internal reflection fluorescence microscopy (TIRFm) and structured illumination microscopy (SIM) were used to visualize the relationship between ER-PM junctions and the cortical actin network.
• Functional assays were performed to assess the impact of F-actin integrity on cellular processes at ER-PM junctions.

Main Results:

• ER-PM junctions in HeLa cells exhibit an average oblong shape with dimensions of approximately 120 nm × 80 nm.
• The cortical actin cytoskeleton plays a significant role in the spatial distribution and stability of ER-PM junctions.
• An intact F-actin architecture is essential for maintaining phosphatidylinositol 4,5-bisphosphate homeostasis at ER-PM junctions, mediated by the protein Nir2.

Conclusions:

• This study provides quantitative insights into the spatial organization of ER-PM junctions.
• The actin cytoskeleton is a key regulator of ER-PM junction organization and function.
• Dynamic remodeling of the actin cytoskeleton offers a mechanism for differential regulation of ER-PM junction activities during cellular processes.