LOCALIZATION OF HYALURONAN IN MOUSE EMBRYOS DURING IMPLANTATION, GASTRULATION AND ORGANOGENESIS

Hyaluronan was localized in postimplantation mouse embryos using CD44, the principal hyaluronan receptor. The specificity of CD44 receptor-g lobulin labelling was confirmed using Streptomyces hyaluronidase, anti -chondroitin sulfate antibody, and other receptor globulins. Our major findings are summarized as follows: 1. Implantation of the blastocyst into the uterine wall triggers a rapid loss of hyaluronan from the ex tracellular matrix of decidual cells on the anti-mesometrial side of t he uterus. 2. Hyaluronan appears early in development in the yolk cavi ty, and the basement membranes of primitive ectoderm and primitive end oderm. 3. During gastrulation, mesodermal cells enter a hyaluronan-ric h environment, but lack a pericellular hyaluronan coat themselves. 4. In limb bud embryos, hyaluronan is present throughout the cranial mese nchyme, but is generally not present in the branchial bars, somites, o r limb buds. 5. At mid-gestation, hyaluronan is present in the axial s keleton, craniofacial mesenchyme, endocardial cushions of the heart, s mooth muscle of the gastrointestinal tract, and connective tissue thro ughout the body. The pattern of hyaluronan expression in the day 13 fe tus is nearly identical to the published distribution of transforming growth factor beta (TGF beta), suggesting a close functional relations hip between these molecules. Together, the results suggest that hyalur onan is involved in the formation of early mesoderm, differentiation o f craniofacial mesenchyme, and morphogenesis of the axial skeleton.