The Ror family of receptor tyrosine kinases consists of two structurally related proteins, Ror1 and Ror2. Ror1 is a pseudokinase that acts as a substrate for the oncogenic tyrosine kinase Met []. It is expressed during development []. It shows no significant expression in normal adult tissues, but it is selectively overexpressed in a number of malignancies []. Ror2 functions as a Wnt receptor required to maintain basal NMDAR-mediated synaptic transmission []. For a time its ligand remained elusive, hence the name receptor tyrosine kinase-like orphan receptor-2 (Ror2). It is now established that Wnt5A acts a ligand for Ror2 [].
The cysteine-rich domain (CRD) is an essential part of the tyrosine kinase-like orphan receptor (Ror) proteins, a conserved family of tyrosine kinases that function in various processes, including neuronal and skeletal development, cell polarity, and cell movement. Ror proteins are receptors of Wnt proteins, which are key players in a number of fundamental cellular processes in embryogenesis and postnatal development. In different cellular contexts, Ror proteins can either activate or repress transcription of Wnt target genes, and can modulate Wnt signaling by sequestering Wnt ligands. In addition, a number of Wnt-independent functions have been proposed for both Ror1 and Ror2 []. Proteins containing this domain also include CAM-1 from C. elegans. CAM-1 is a ROR receptor tyrosine kinase that inhibits the Wnt pathway [].
