Heat shock proteins, HSP25 and HSP70, and apoptosis in developing endocardial cushion of the mouse heart

Formation of the atrioventricular channels and valves from the endocardial cushion occurs through growth and remodeling of the initial endocardial cus hion. This process requires balanced coordination of proliferation and apop tosis by still unknown factors. To detect a possible role for the heat shoc k proteins 25 and 70 (HSP25 and HSP70) as apoptosis-associated proteins and differentiation factors in the development of the endocardial cushion, we analyzed their temporal and regional occurrence during cell proliferation a nd apoptosis in E11-E17 embryos. The distribution and timing of these event s and factors were consistent with the hypothesis that HSP25 is related to myocardial development whereas HSP70 is related to differentiation of the e ndocardial cushion by cell proliferation and apoptosis.