Expression pattern and gene characterization of asporin - A newly discovered member of the leucine-rich repeat protein family

We have discovered a new member of the class I small leucine-rich repeat pr oteoglycan (SLRP) family which is distinct from the other class I SLRPs sin ce it possesses a unique stretch of aspartate residues at its N terminus. F or this reason, we called the molecule asporin. The deduced amino acid sequ ence is about 50% identical (and 70% similar) to decorin and biglycan. Howe ver, asporin does not contain a serine/glycine dipeptide sequence required for the assembly of O-linked glycosaminoglycans and is probably not a prote oglycan. The tissue expression of asporin partially overlaps with the expre ssion of decorin and biglycan. During mouse embryonic development, asporin mRNA expression was detected primarily in the skeleton and other specialize d connective tissues; very little asporin message was detected in the major parenchymal organs. The mouse asporin gene structure is similar to that of biglycan and decorin with 8 exons. The asporin gene is localized to human chromosome 9q22-9q21.3 where asporin is part of a SLRP gene cluster that in cludes extracellular matrix protein 2, osteoadherin, and osteoglycin. Furth er analysis shows that, with the exception of biglycan, all known SLRP gene s reside in three gene clusters.