Figure 5.

Creating a stable boundary through diffusive flux and asymmetries in membrane association/dissociation. Because the regions of net association to and dissociation from the membrane occur in different domains, the source and sink are displaced in space, leading to a buildup of concentration gradients across the cell. These concentration gradients drive flux of molecules across the cell both on the membrane (boundary flux) and in the cytoplasm. At steady state, all of these processes balance, the local concentrations of PAR proteins no longer change with time, and the resulting boundary gradient is stable. Here, we show the proposed schematic of this cycle for the posterior PAR protein, PAR-2, with a region of high PAR-3/PAR-6/aPKC serving as a sink in the anterior (red membrane region). A model for PAR-6 would be similar but with a reversed orientation along the A–P axis and a region of high PAR-2 concentrations serving as a sink.