A histochemical study of sulphated glycosaminoglycans associated with the somites of the chick embryo.

A histochemical study of sulphated glycosaminoglycans associated with the somites of the chick embryo SUMMARY A histochemical analysis has been made of sulphated glycosaminoglycans (mucopoly-saccharides) associated with chick embryo somites before and after the onset of overt cartilage differentiation. The sulphated glycosaminoglycans were distinguished and resolved into different types by the use of alcian blue at low pH and alcian blue 'critical electrolyte con-centration' staining combined with hyaluronidase digestion. The newly formed somites are bounded on their dorsal, ventral, and medial surfaces by basement membrane material as they are delimited from the unsegmented paraxial mesoderm Such epithelial basement membrane material, which was first detected in association with the epiblast/mesoderm boundary in the stage-4 embryo, was found to contain a major chon-droitin sulphate A/C fraction and a minor chondroitin sulphate B fraction. The notochord sheath contained similar sulphated glycosaminoglycans. Sulphated glycosaminoglycans were first detected between cells of the somite 'core' at stage 14 and were subsequently seen to accumulate around the cells of the developing sclero-tome and later around cells of the dermatome; the myotome was devoid of such material at these stages (stage 14-20). These pre-cartilaginous sulphated glycosaminoglycans were also of the chondroitin sulphate A/C plus chondroitin sulphate B types. In contrast, the matrix material of newly forming vertebral cartilage, which was first seen in the anterior region of stage 21 embryos, was distinguished by its lack of a hyaluronidase-resistant sulphated glycosaminoglycan component, and therefore presumably contained only chondroitin sulphates A/C. Much later in development (after stage 33) small amounts of sulphated glycosaminoglycan with the staining properties of keratan sulphate were found in the perichordal and subperichondrial regions of the vertebral cartilage.