Fibroblast growth factor receptor-like 1 (FGFRL1) also known as Fibroblast growth factor receptor 5 (FGFR5), is a member of the fibroblast growth factor receptor (FGFR) family, where amino acid sequence is highly conserved between members and throughout evolution. A full-length representative protein would consist of an extracellular region, composed of three immunoglobulin-like domains, a single hydrophobic membrane-spanning segment and a cytoplasmic tyrosine kinase domain. The extracellular portion of the protein interacts with fibroblast growth factors, setting in motion a cascade of downstream signals, ultimately influencing mitogenesis and differentiation. A unique feature of FGFRL1/FGFR5 is that it does not contain an intracellular tyrosine kinase domain. Some muscle types, including the muscles of the tongue and the diaphragm, express FGFRL1/FGFR5 at relatively high level. In contrast, the heart and the skeletal muscles of the limbs, as well as many other organs (brain, lung, liver, kidney, gut) express Fgfrl1 only at basal level. It is conceivable that FGFRL1/FGFR5 interacts with other Fgfrs, which are expressed in cartilage and muscle, to modulate FGF signaling.
