Endocrine Abstracts

Heparan sulphate (HS) is a highly complex linear polysaccharide found attached to core proteins both on the cell surface and in the extracellular matrix. Newly synthesized HS chains are modified by a family of enzymes, many of which have multiple isoforms with differing substrate preferences. These modifications include the addition of sulphate groups at up to four positions on each disaccharide unit. The pattern of modifications a HS saccharide undergoes alters its structure, affecting the ability of the HS to bind and regulate many different growth factors (such as FGFs and BMPs) known to have roles in stem cell regulation. HSs are thus expected to be pivotal molecules involved in controlling stem cell behaviour.

We have been studying the molecular phenotype of HS biosynthesis and structure during mouse ES cell differentiation in both neural differentiation and embryoid body formation. Embryoid bodies (EBs) are layered, ordered aggregates of cells made up of primitive endoderm cells overlaying an epithelium of epiblast cells, separated by a basement membrane and surrounding a central cavity. The generation of EBs from undifferentiated ES cells has been used as a model for early development and has been shown to require signalling through fibroblast growth factor (FGF) receptor 2, implicating HS which is a necessary co-receptor for the formation of a signalling complex. We have observed dynamic spatiotemporal expression patterns of HS (using a panel of anti-HS antibodies), its biosynthetic enzymes, HS core proteins and FGFRs during ES cell differentiation. Variant HS structures could thus provide a basis for regulation of signalling mechanisms in ES cell differentiation. These studies provide a platform for dissection of the structural requirements for the functional role of HS in regulating critical aspects of stem cell differentiation.