Abstract
The amino acid sequence of rat N-syndecan core protein was deduced from the cloned cDNA sequence. The sequence predicts a core protein of 442 amino acids with six structural domains: an NH2-terminal signal peptide, a membrane distal glycosaminoglycan attachment domain, a mucin homology domain, a membrane proximal glycosaminoglycan attachment domain, a single transmembrane domain, and a noncatalytic COOH-terminal cytoplasmic domain. Transfection of human 293 cells resulted in the expression 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 molecular weight of 120, 000, identical to N-syndecan synthesized by neonatal rat brain or Schwann cells. Rat genomic DNA coding for N-syndecan was isolated by hybridization screening. The rat N-syndecan gene is comprised of five exons. Each exon corresponds to a specific core protein structural domain, with the exception of the fifth exon, which contains the coding information for both the transmembrane and cytoplasmic domains as well as the 3'-untranslated region of the mRNA. The first intron is large, with a length of 22 kilobases. The expression of N-syndecan was investigated in late embryonic, neonatal, and adult rats by immunoblotting and Northern blotting analysis. Among the tissues and developmental stages studied, high levels of N-syndecan expression were restricted to the early postnatal nervous system. N-syndecan was expressed in all regions of the nervous system, including cortex, midbrain, spinal cord, and peripheral nerve. Immunohistochemical staining revealed high levels of N-syndecan expression in all brain regions and fiber tract areas.
Highlights
The syndecans are a gene family of transmembrane cell surface proteoglycans
We reported the cloning of a partial cDNA sequence from neonatal rat Schwann cells that coded for the syndecan core protein, which we called N-syndecan [9]
Cloning and Sequence Analysis of Rat N-syndecan cDNA— Previously, we reported the cloning of a partial rat N-syndecan cDNA that was truncated at the 5Ј end
Summary
The syndecans are a gene family of transmembrane cell surface proteoglycans (reviewed in Refs. 1 and 2). Syndecan core proteins are characterized by highly conserved transmembrane and noncatalytic COOH-terminal cytoplasmic domains but structurally distinct extracellular domains This modular structural design suggests that individual mammalian syndecans have evolved to carry out specific functions within the tissues where they are expressed, probably related to the binding of specific extracellular ligands, but that these may be linked to common intracellular activities. We reported the cloning of a partial cDNA sequence from neonatal rat Schwann cells that coded for the syndecan core protein, which we called N-syndecan [9]. This proteoglycan is expressed in the central nervous system.
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