Immunolocalization and heart levels of GRP94 in the mouse during post-implantation development.

Glucose-regulated proteins (GRPs), which belong to the highly conserved family of stress proteins, are resident to the endoplasmic reticulum and function as molecular chaperones. Heat shock proteins have been shown to be developmentally regulated, but little work has been done to investigate the expression of GRPs during embryogenesis. Therefore, this study examined the distribution of GRP94 within mouse embryos during the period of organogenesis and characterized levels of GRP94 within the developing heart during organogenesis and late fetal stages. Our results demonstrate that the GRP94 protein is constitutively expressed within mouse embryos during early stages of organogenesis and is localized particularly within the developing heart, neuroepithelium, and surface ectoderm tissues. Positive staining for GRP94 remains within developing heart tissues throughout organogenesis and is found primarily within the atrial and ventricular myocardial cells. Western blot analysis of GRP94 expression demonstrates a significantly higher level of GRP94 in embryonic hearts during early stages of organogenesis than in later stages of organogenesis or the fetal period. These results demonstrate that the stress protein GRP94 is constitutively expressed within specific tissues during post-implantation mouse development and suggest that GRPs may play an important role in the process of myocardial cell differentiation and heart development.