STRUCTURE, REGULATION AND FUNCTION OF AVIAN GLYPICAN

Glypicans are a group of membrane-bound heparan sulfate proteoglycans (HSPG) that are tissue specific and developmentally regulated. Transcr ipts for avian glypican are found in endocardial cushions, limb buds, somites and forebrain of early chick embryos. Since avian glypican is not well characterized, the cellular localization. regulation of expre ssion, and possible function during cardiac development have been stud ied. A polyclonal antibody was raised against a 20-amino acid peptide corresponding to an antigenic sequence within avian glypican core prot ein. The antibody recognized the expressed core protein in bacterial l ysates and the endogenous HSPG in the proteoglycan fraction from chick forebrain. Immunolocalization studies indicated that the core protein is associated with cell membranes. The level of mRNA for avian glypic an in MEQC (myc embryonic quail cardiomyocytes) grown in medium contai ning 10% fetal calf serum was compared to the message levels in cells grown without serum for 3 days. By Northern analysis, glypican transcr ipts were increased markedly after serum starvation. Up-regulation of glypican transcripts by serum withdrawal was partially prevented by ad dition of TGF beta-1 and bFGF, suggesting that these growth factors ma y regulate its expression. MEQC cells deprived of serum migrated into clumps that could be blocked by an antisense OND (oligodeoxynucleotide ) to the mRNA encoding the avian glypican. The same antisense OND inhi bited the migration of endothelial cells from chick tubular heart expl ants over the surface of collagen gels. These results indicate that av ian glypican may play a role in cell migration during development of e ndocardial cushions. (C) 1998 Academic Press Limited.