IMMUNOLOCALIZATION AND HEART LEVELS OF GRP94 IN THE MOUSE DURING POSTIMPLANTATION DEVELOPMENT

Glucose-regulated proteins (GRPs), which belong to the highly conserve d family of stress proteins, are resident to the endoplasmic reticulum and function as molecular chaperones. Heat shock proteins have been s hown to be developmentally regulated, but little work has been done to investigate the expression of GRPs during embryogenesis. Therefore, t his study examined the distribution of GRP94 within mouse embryos duri ng the period of organogenesis and characterized levels of GRP94 withi n the developing heart during organogenesis and late fetal stages. Our results demonstrate that the GRP94 protein is constitutively expresse d within mouse embryos during early stages of organogenesis and is loc alized particularly within the developing heart, neuroepithelium, and surface ectoderm tissues. Positive staining for GRP94 remains within d eveloping heart tissues throughout organogenesis and is found primaril y within the atrial and ventricular myocardial cells. Western blot ana lysis of GRP94 expression demonstrates a significantly higher level of GRP94 in embryonic hearts during early stages of organogenesis than i n later stages of organogenesis or the fetal period. These results dem onstrate that the stress protein GRP94 is constitutively expressed wit hin specific tissues during post-implantation mouse development and su ggest that GRPs may play an important role in the process of myocardia l cell differentiation and heart development.