FERM Domain Containing Protein 4A (FRMD4A)

FRMD4A was sufficient and necessary for the localization at spot-like AJs and TJs. Cytohesin-1-FRMD4A-Par-3 forms a ternary complex. Full-length FRMD4A was recruited to Par-3 containing AJs regardless of cytohesin-1. The deletion mutant of cytohesin-1 lacking its coiled-coil domain, which is responsible for the binding to FRMD4A, does not colocalize with Par-3 and FRMD4A at AJs. The deletion mutant of FRMD4A lacking Par3BD cannot recruit full-length cytohesin-1 to Par-3-containing spot-like AJs. Cooperative recruitment of cytohesin family proteins to primordial AJs by FRMD4A and GRSP-1 is essential for the epithelial polarization.  FRMD4A and GRSP-1 are recruited to primordial AJs through direct binding to Par-3 and in turn recruit cytohesin family proteins, which are the Arf6 guanine-nucleotide exchange factors.