Glycosaminoglycan synthesis in rat embryos during the formation of the primary mesenchyme and neural folds

Abstract

Glycosaminoglycan (GAG) synthesis was studied in explanted rat embryos on Days 7 (preprimitive streak), 8 (primitive streak), 9 (0–4 somites), and 10 (6–10 somites) by labeling with [ 3H]glucosamine or 35SO 4. Specific GAG were identified by electrophoresis and sensitivity to degradation by specific enzymes or treatments. By these criteria, the labeled GAG were identified as either hyaluronic acid, chondroitin or chondroitin sulfates, or heparan sulfate. In the Day 7 embryo proper, glucosamine was equally incorporated into hyaluronate, chondroitin or chondroitin sulfate, and heparan sulfate, whereas, by Day 9, about 83% of the glucosamine-labeled GAG was hyaluronate, 5% in chondroitin or chondroitin sulfate and 11% in heparan sulfate. When expressed as glucosamine counts incorporated per microgram of protein, this represents a 16-fold increase in hyaluronate during the formation of the primary mesenchyme. Similar GAG were made by both the anterior and posterior halves of the embryo, but the anterior half incorporated 1.75 times as much glucosamine into isolated GAG as did the posterior half. In the extraembryonic tissues, about 24% of the label was in hyaluronic acid, 44% in chondroitin or chondroitin sulfate, and 35% in heparan sulfate. There were no stage-related changes in the patterns of labeling in the extraembryonic tissues. It is shown that increased hyaluronic acid synthesis in the embryo is correlated with the formation of the primary mesenchyme and its associated cell free spaces and the neural folds.