The CS sulphation motifs 4C3, 7D4, 3B3[-]; and perlecan identify stem cell populations and niches, activated progenitor cells and transitional tissue development in the fetal human elbow

We compared the immunohistochemical distribution of (i) the novel chondroitin sulphate (CS) sulphation motifs 7D4, 4C3 and 3B3[-], (ii) native heparan sulphate (HS) and Δ-HS ‘stubs’ generated by heparitinase III digestion and (iii) the HS-proteoglycan, perlecan, in the foetal human elbow joint. Putative stem cell populations associated with hair bulbs, humeral perichondrium, humeral and ulnar rudiment stromal/perivascular tissues expressed the CS motifs 4C3, 7D4 and 3B3[-] as well as perlecan in close association but not co-localised. Chondrocytes in the presumptive articular cartilage of the foetal elbow expressed the 4C3 and 7D4 CS sulphation motifs consistent with earlier studies on the expression of these motifs in knee cartilage following joint cavitation. The present study also indicated that hair bulbs, skin, perichondrium and rudiment stroma were all perlecan rich progenitor cell niches that contributed to the organisation and development of the human foetal elbow joint and associated connective tissues. One of the difficulties in determining the precise role of stem cells in tissue development and repair processes is their short engraftment period and the lack of specific markers which differentiate the activated stem cell lineages from the resident cells. The CS sulphation motifs 7D4, 4C3 and 3B3[-] decorate cell surface proteoglycans on activated stem/progenitor cells and thus can be used to identify these cells in transitional areas of tissue development and in repair tissues and may be applicable to determining a more precise mode of action of stem cells in these processes. Isolation of perlecan from 12-14 week gestational age foetal knee rudiments demonstrated that perlecan in these foetal tissues was a HS-CS hybrid proteoglyca