The LRR and Ig domain-containing membrane protein SST273 is expressed on motoneurons

We performed signal sequence trap cDNA cloning using a cDNA library of enriched chicken embryonic spinal motoneurons and identified a novel transmembrane molecule, SST273 (Signal Sequence Trap clone 273). SST273 has five leucine-rich repeats (LRRs) and one immunoglobulin (Ig) domain in its extracellular domain. The human (KIAA1465) and mouse (BC059068) homologues of SST273 were already cloned, but had not yet been analyzed. The amino acid homologies between chick SST273 and human or mouse homologue are 52.1 and 51.5%, respectively. SST273 mRNA and its protein product were uniquely expressed in the embryonic spinal and cranial motoneurons at early developmental stages.