Sema4D (Semaphorin-4D) is a cell surface receptor for PLXN1B and PLXNB2 that plays an important role in cell-cell signaling. Sema4D promotes reorganization of the actin cytoskeleton and plays a role in axonal growth cone guidance in the developing central nervous system. Sema4D regulates dendrite and axon branching and morphogenesis. It promotes the migration of cerebellar granule cells and of endothelial cells. In the immune system Sema4D induces B-cells to aggregate and improves their viability (in vitro). Sema4D also promotes signaling via SRC and PTK2B/PYK2, which then mediates activation of phosphatidylinositol 3-kinase and of the AKT1 signaling cascade [taken from the Universal Protein Resource (UniProt) www.uniprot.org/uniprot/Q92854].