A cDNA encoding a protein designated as LIG-1 has been cloned and characterized. A fragment of this cDNA was found previously in a screen for genes up-regulated during neural differentiation in mouse P19 embryonal carcinoma cells. Comparative sequence analysis revealed LIG-1 to be a novel integral membrane glycoprotein (1091 amino acids) containing an extracellular region (794 amino acids) with a potential signal peptide, 15 leucine-rich repeats, 3 immnunoglobulin-like domains, and 7 potential N-glycosylation sites, a transmembrane region of 23 amino acids, and a cytoplasmic region of 274 amino acids. This protein, therefore, is a new member of both the leucine-rich repeat and the immunoglobulin superfamilies. Furthermore, Northern blot and in situ hybridization analyses showed LIG-1 gene expression to be predominantly in the brain, restricted to a small subset of glial cells such as Bergmann glial. cells of the cerebellum and glial cells in the nerve fiber layer of the olfactory bulb. On the basis of its structural features and expression pattern, we propose that LIG-1 functions as a cell type-specific adhesion molecule or receptor at the glial cell surface, and plays a role in the nervous system in for example neuroglial differentiation, development, and/or maintenance of neural functions where it is expressed.
