Fibronectin Leucine-Rich Transmembrane (FLRT) proteins are glycosylated membrane proteins expressed at the cell surface which localise in a homophilic manner to cell-cell contacts expressing the focal adhesion marker vinculin. FLRT1, FLRT2, and FLRT3, the three genes encode putative type I transmembrane proteins, each containing 10 leucine-rich repeats (LRR), a type III fibronectin (FN) domain, followed by the transmembrane region, and a short cytoplasmic tail. FLRT family members may function in cell adhesion and/or receptor signalling. Each member of the FLRT family has a distinct, highly regulated expression pattern, as was seen for the NLRR family. FLRT2 is expressed in a subset of the sclerotome, adjacent to the region that forms the syndetome, suggesting that interaction with FGF signalling may be a general property of FLRT proteins. All FLRTs can interact with FGFR1 and FLRTs can be induced by the activation of FGF signalling by FGF-2. FLRT proteins have a dual role, promoting FGF signalling and modulating homotypic cell adhesion. FLRT2 played critical roles in craniofacial development, and it was also present in the vomero-nasal organ, mandibular primodia, and the posterior aspects of the unfused and fused secondary palatal shelves.
