Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos. II. Autoradiographic observations on the sites of synthesis and mode of transport of galactose- and glucosamine-labelled materials.

Pulse-chase labelling experiments and light- and electron-microscopic autoradiography were used to examine the sites of synthesis, mode of transport, and sites of deposition of galactose- and glucosamine-labelled materials in different developmental stages of normal developing Rana pipiens embryos and interspecific hybrid embryos formed by fertilizing the eggs of R. pipiens with the sperm of R. catesbeiana. In both normal and hybrid embryos, after 15-min pulse, grains are closely associated with juxtanuclear and cytoplasmic collections of membrane-bound vesicles which resemble the Golgi apparatus. In normal embryos following a 15-30 min pulse and a 60-min chase, grains are largely cleared from the cytoplasmic vesicles and deposited in the extracellular spaces or along cell surfaces where the extracellular spaces are relatively large. In contrast, arrested hybrid embryos given a 15-30-min pulse and a 60-min chase show a marked accumulation of grains over cytoplasmic structures such as the Golgi apparatus and vesicular elements in the cell cortex. Finally, early gastrula stage normal embryos are most active in the synthesis of galactose-labelled materials in cells above the dorsal lip of the blastopore, where cell migration is initiated.