Basal Lamina Glycosaminoglycans

One principal family of proteins in the basal lamina are the glycosaminoglycans (GAG). These proteins have a twofold role as they both allow for epidermal cell proliferation to expand the stalks and lobules of the glands and they then help maintain these differentiated stalks. Without them, the basal lamina will break down and disappear, and without the basal lamina, the branched morphology of the salivary gland does not remain (Handbook of Physiology, 1989). Basal lamina distribution along the epidermal layer is determined by the continual breakdown and replacement of GAG. Different areas of the basal lamina have different amounts of GAG, due to the selective breakdown of GAG (Bernfield and Banerjee, 1982). The mesenchymal cells are responsible for this breakdown process of GAG which allows for the epithelium to touch the mesenchyme in areas where the mesenchyme has stopped GAG production. The difference in basal lamina breakdown may be due to the specificity of the GAG itself. In the epithelial clefts, GAG may be stabilized by the collagen which lines up there. The basal lamina at the distal lobules of the branching glands, where the epithelium and the mesenchyme meet, is not covered by this collagen layer. Therefore, the basal lamina may be more susceptible to being broken down by hyaluronidase secreted by the mesenchyme (Bernfield and Banerjee, 1982). Collagen may play a part in protecting the basal lamina from hyaluronidase (Gilbert, 1994).

The breakdown of the basal lamina by these glycosaminoglycans may allow for the continued development of epithelial branching. If the basal lamina is selectively removed from the surface of the epithelium, the epithelial cells could then continue to proliferate to expand the developing glands (Gilbert, 1994). So the epithelium needs the correct signals from the mesenchyme to continue its growth.

Return to Epithelium Morphogenesis