Histochemical analysis of extracellular matrix material in embryonic mouse lens morphogenesis

Extracellular matrix material (ECM) present during mouse lens morphogenesis was studied histologically by the periodic acid-Schiff, Alcian blue 8GX, pH 2.5, high iron diamine, and Van Gieson methods, and enzymatically with bovine testicular hyaluronidase, Streptomyces hyaluronidase, malt diastase, and collagenase. The basal lamina of the optic vesicle prior to lens placode formation was found to be higher in glycosaminoglycan (GAG) content than was the ectodermal basal lamina. Upon apposition of the optic vesicle and presumptive lens ectoderm, the ECM plus basal laminae appeared as the equivalent of adding both optic vesicle-associated and ectodermal-associated basal lamina. The proposal is made that the initial triggering mechanism of lens morphogenesis consists of a cross-linking and polymerization of optic vesicle-associated GAG to ectodermal-associated glycoproteins resulting in a firm attachment between the structures. Basal lamina associated with the presumptive pigmented retina and also the more ventral part of the interface matrix were found to change from predominantly GAG in early stages to collagen deposits in more advanced stages, temporally coinciding with the appearance of differentiative markers in each structure. This pattern of GAG turnover and replacement by collagen during the course of development is also seen in mouse salivary gland morphogenesis (M. R. Bernfield, S. D. Banerjee, and R. H. Cohn (1972). J. Cell Biol. 52, 674-686.).