EXPRESSION OF A XENOPUS COUNTERPART OF MAMMALIAN SYNDECAN-2 DURING EMBRYOGENESIS

We have identified a Xenopus cDNA, XS-2, by screening a Xenopus embryo nic stage-22-24 cDNA library with a DNA probe encoding the transmembra ne and cytoplasmic domains of mouse syndecan 1. The 1.4 kb cDNA consis ts of an open reading frame of 642 nucleotides encoding a protein of 1 91 amino acids. The predicted protein of 20869 Da contains a 25-amino acid putative transmembrane domain and a 32-amino acid putative cytopl asmic domain, both of which are highly similar to the corresponding re gions of rat syndecan 2 (92 % identity) and to a lesser degree those o f rat syndecans 1, 3 and 4 (62, 64 and 78 % respectively). The putativ e N-terminal ectodomain contains a possible attachment site for hepara n sulphate, identical with the comparable glycosaminoglycan-attachment sequence of rat syndecan 2. Polyclonal antisera raised against recomb inant ectodomain of XS-2, expressed as a fusion protein, recognized a heparan sulphate proteoglycan in XTC-cell-culture medium. This proteog lycan bound to DEAE-Sephacel and was eluted with 1M NaCl; digestion wi th heparitinase but not chondroitinase ABC resulted in the identificat ion of a 46 kDa protein by these antisera. Northern-blot analysis indi cated that XS-2 identifies two Xenopus mRNA species approx, 4 and 2 kb in size in embryos ranging in maturation from the 64-cell stage to st age 54. These results demonstrate that a heparan sulphate proteoglycan , similar to syndecan 2, is expressed during Xenopus embryogenesis.