CDNA CLONING, GENOMIC ORGANIZATION, AND IN-VIVO EXPRESSION OF RAT N-SYNDECAN

The amino acid sequence of rat N-syndecan core protein was deduced fro m the cloned cDNA sequence. The sequence predicts a core protein of 44 2 amino acids with six structural domains: an NH2-terminal signal pept ide, a membrane distal glycosaminoglycan attachment domain, a mucin ho mology domain, a membrane proximal glycosaminoglycan attachment domain , a single transmembrane domain, and a noncatalytic COOH-terminal cyto plasmic domain. Transfection of human 293 cells resulted in the expres sion of N-syndecan that was modified by heparan sulfate chain addition . Heparitinase digestion of the expressed proteoglycan produced a core protein that migrated on SDS-polyacrylamide gels at an apparent molec ular weight of 120,000, identical to N-syndecan synthesized by neonata l rat brain or Schwann cells. Rat genomic DNA coding for N-syndecan wa s isolated by hybridization screening. The rat N-syndecan gene is comp rised of five exons. Each exon corresponds to a specific core protein structural domain, with the exception of the fifth exon, which contain s the coding information for both the transmembrane and cytoplasmic do mains as well as the 3'-untranslated region of the mRNA. The first int ron is large, with a length of 22 kilobases. The expression of N-synde can was investigated in late embryonic, neonatal, and adult rats by im munoblotting and Northern blotting analysis. Among the tissues and dev elopmental stages studied, high levels of N-syndecan expression were r estricted to the early postnatal nervous system. N-syndecan was expres sed in all regions of the nervous system, including cortex, midbrain, spinal cord, and peripheral nerve. Immunohistochemical staining reveal ed high levels of N-syndecan expression in all brain regions and fiber tract areas.