Glycosaminoglycan localization and role in maintenance of tissue spaces in the early chick embryo1
Comparison of sections stained with Alcian blue at pH 1·0 or 2·5 demonstrates the distribution of sulfated and non-sulfated glycosaminoglycans in the extracellular matrix of the stage-8 (Hamburger & Hamilton, 1951) chick embryo. Both types of GAG are present in basement membranes throughout the embryo. Treatment of sections with Streptomyces hyaluronidase, reported to be specific for hyaluronic acid, prior to staining with Alcian blue at pH 2·5 reveals that hyaluronate is an important constituent of the extracellular matrix in basement membranes and in intercellular spaces within the mesoderm. Hyaluronate is shown to be the predominant glycosaminoglycan in the matrix of the head mesenchyme. In addition, examination by SEM and light microscopy of embryos after treatment in ovo with hyaluronidase shows that removal of hyaluronate from living embryos results in a dramatic decrease in cell-free spaces and a weakening of the association between mesoderm and ectoderm in the head.