Isoform-specific expression of BAG-1 in mouse development

BAG-1 is a family of proteins with diverse activities that range in culture d cells from protection against programmed cell death through to regulation of steroid hormone action. At least three proteins (BAG-1L, BAG-1M and BAG -1) are encoded by the Bag-1 mRNA through the use of alternative translatio n-initiation sites. To assess the in vivo function of these factors, we hav e used in situ hybridization and immunohistochemical techniques to determin e the distribution of Bag-1 transcript and proteins during mouse developmen t. Bag-1 mRNA was identified in several organs with cartilaginous tissues s howing the highest expression levels. The level of expression at some of th ese sites was downregulated during the course of development. In the immuno histochemical studies, antibodies directed against the BAG-1 proteins stain ed all the sites identified in the in situ hybridization studies although i soform-specific differences were observed. BAG-1L specific antibody showed ubiquitous staining as early as day 10.5 post-coitum but there was a progre ssive restriction during subsequent stages of embryogenesis. On the contrar y, an antibody that preferentially recognized the other isoforms only stain ed the mouse myocardium in the early developmental stages before finally re cognizing additional organs later on in development. These results demonstr ate a stage- and site-specific expression of the BAG-1 isoforms during mous e development. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.