INDUCTION OF A HYALURONAN RECEPTOR, CD44, DURING EMBRYONAL CARCINOMA AND EMBRYONIC STEM-CELL DIFFERENTIATION

This paper describes the expression profile of the CD44 glycoprotein d uring differentiation of embryonal carcinoma (EC) and embryonic stem ( ES) cells. We have recently shown that CD44 is expressed in discrete e mbryonic structures and, in view of this, we sought an in vitro differ entiation model of development in which we could study more readily th e structure and function of the CD44 molecule. The P19 EC and CGR8 ES cells were chosen as they have the capacity to develop down the cardia c muscle pathway and we have previously demonstrated that CD44 is expr essed abundantly in the embryonic myocardium. The differentiation proc ess in both cell types is accompanied by an induction of CD44 mRNA and protein. However, in differentiated cultures CD44 is not expressed in contractile cells, indicating that these P19 cells do not represent C D44-positive embryonic cardiomyocytes. Expression of CD44 is observed on fibroblast-like cells which appear to migrate over and out from the plated aggregates. Hyaluronan, the major ligand for CD44, is also ass ociated with these CD44-positive fibroblast-like cells. It is suggeste d that expression of bath receptor and ligand by the fibroblastic cell s is required for cell:matrix adhesion and cell motility. As CD44 is u p-regulated in these cultures, P19 cells are now established as a usef ul model system to study the factors regulating expression of the CD44 gene.