We have cloned and determined the genomic organization of the core pro
tein of the chicken transmembrane proteoglycan, syndecan-4. Identifica
tion of the initial cDNA was accomplished using polyclonal antibodies
directed against the cytoplasmic domain of murine syndecan-1 core prot
ein. The cDNA for chicken syndecan-4 encodes a putative core protein o
f 197 amino acids which consists of a 19-amino acid signal peptide, a
125-amino acid ectodomain, a 25-amino acid transmembrane domain, and a
28-amino acid cytoplasmic domain. The predicted molecular mass of the
mature core protein is 19,639 daltons. The ectodomain of chicken synd
ecan-4 core protein contains three potential sites for glycosaminoglyc
an attachment, two sites for N-glycosylation, and lacks a dibasic prot
ease cleavage site proximal to the membrane-spanning region found in o
ther syndecan family members. Comparison of the complete amino acid se
quence with human syndecan-4 (amphlican (David, G., van der Schueren,
B., Marynen, P., Cassiman, J. J., and van den Berghe, H. (1992) J. Cel
l Biol. 118, 961-969)) and rat syndecan-4 (ryudocan (Kojima, T., Shwor
ak, N. W., and Rosenberg, R. D. (1992) J. Biol. Chem. 267, 4870-4877))
indicates an overall identity of 58 and 56%, respectively, with a 91
and 92% identity in the highly conserved transmembrane and cytoplasmic
domains. The core protein of chicken syndecan-4 synthesized by chicke
n cells is modified with heparan sulfate side chains yielding a proteo
glycan with a molecular mass of >200 kDa in LMH cells (immortalized ma
le leghorn LM strain hepatocytes) and primary skin fibroblasts. Syndec
an-4 isolated from chondrocyte cultures runs as a diffuse band between
100 and 200 kDa. Northern analysis of chicken syndecan-4 indicates th
ree messages with distinct sizes of 0.9, 1.3, and 2.9 kb and a wide mR
NA tissue distribution. The chicken syndecan-4 gene is divided into 5
exons encoding distinct regions which contain the signal peptide, the
glycosaminoglycan attachment sites, a small spacer of unknown function
, the glycosylation sites and the transmembrane and cytoplasmic domain
s.