Immunoglobulin Superfamily, Member 9 (IGSF9)

By searching for cDNAs encoding large proteins expressed in brain, Nagase et al. (2000) cloned IGSF9, which they called KIAA1355. The predicted 1,189-amino acid protein has multiple fibronectin (FN) type III and immunoglobulin (Ig) domains. RT-PCR ELISA detected highest expression in liver and moderate expression in testis, ovary, and fetal brain. All other tissues examined, including adult brain, showed little to no expression.

The 1,179-amino acid mouse and human proteins are 87% identical. The IGSF9 protein structure is typical of NCAM family members, consisting of an N-terminal signal peptide, an extracellular domain containing 5 Ig-like and 2 FN-III domains, a transmembrane domain, and a C-terminal cytoplasmic region.