Glucocorticoid receptor gene expression during rat embryogenesis. An in situ hybridization study.

Glucocorticoids play an important role in embryonic development. The existence of sufficient amounts of their receptors during rodent embryogenesis has proved to be an absolute necessity for the physiological growth of the animal. We have analyzed the pattern of glucocorticoid receptor gene expression in the rat embryo through embryonic days 12 to 17, by using in situ hybridization histochemistry. Glucocorticoid receptor mRNA is present in the rat liver on embryonic day (E) 12, and by E13 the signal can also be detected in several other tissues, such as the lung, the heart, the mesonephros, the sclerotomes, the thymus and Rathke's pouch. Glucocorticoid receptor gene expression was quite ubiquitous in tissue derivatives of all three germ layers and appeared to vary in intensity within the same tissue during embryogenesis. These variations in the level of receptor gene expression paralleled the developmental stage of each tissue: Intense labelling was detected just prior to the final differentiation step of a structure. Upon differentiation, cell populations highly expressing glucocorticoid receptor gene in the previous stage were found to have reduced amounts of the receptor mRNA. Our results support a morphogenetic role for glucocorticoids during embryogenesis.