Partitioning of ribonucleoprotein complexes from the cellular actin cortex

The cell cortex plays a crucial role in cell mechanics, signaling, and
development. However, little is known about the influence of the cortical
meshwork on the spatial distribution of cytoplasmic biomolecules. Here, we
describe a new fluorescence microscopy method to infer the intracellular
distribution of labeled biomolecules with sub-resolution accuracy.
Unexpectedly, we find that RNA-binding proteins are partially excluded
from the cytoplasmic volume adjacent to the plasma membrane that
corresponds to the actin cortex. Complementary diffusion measurements of
RNA-protein complexes suggest that a rudimentary model based on excluded
volume interactions can explain this partitioning effect. Our results
suggest the actin cortex meshwork may play a role in regulating the
biomolecular content of the volume immediately adjacent to the plasma
membrane.