The reggie/flotillin connection to growth.

The proteins reggie-1 and reggie-2 were originally discovered in neurons during axon regeneration. Subsequently, they were independently identified as markers of lipid rafts in flotation assays and were hence named flotillins. Since then, reggie/flotillin proteins have been found to be evolutionarily conserved and are present in all vertebrate cells - yet their function has remained elusive and controversial. Recent results now show that reggie/flotillin proteins are indeed necessary for axon regeneration and growth: no axons form when reggies/flotillins are downregulated and signaling pathways controlling actin dynamics are perturbed. Their widespread expression and conservation, however, suggest that these proteins regulate basic cellular functions beyond regeneration. It is argued here that the reggie/flotillin proteins regulate processes vital to all cells - the targeted delivery of bulk membrane and specific membrane proteins from internal vesicle pools to strategically important sites including cell contact sites, the T cell cap, regenerating axons and growth cones and other protrusions.