Mist1 expression is a common link among serous exocrine cells exhibiting regulated exocytosis

Mist1 is a basic helix-loop-helix transcription factor that represses E-box -mediated transcription. Previous studies have suggested that the Mist1 gen e is expressed in a wide range of tissues, although a complete characteriza tion of Mist1 protein accumulation in the adult organism has not been descr ibed. In an effort to identify specific cell types that contain the Mist1 p rotein, antibodies specific for Mist1 were generated and used in Western bl ot and immunohistochemical assays. Our studies show that the Mist1 protein is present in many different tissues but that it is restricted to cell type s that are exclusively secretory in nature. Pancreatic acinar cells, serous or seromucous cells of the salivary glands, chief cells of the stomach, an d secretory cells of the prostate and seminal vesicle show high levels of M ist1 protein, whereas nonserous exocrine cells, including the mucus-produci ng cells of the salivary glands, remain Mist1 negative. These results ident ify Mist1 as the first transcription factor that exhibits this unique serou s-specific expression pattern and suggest that Mist1 may have a key role in establishing and maintaining a pathway responsible for the exocytosis of s erous secretions. Anat Rec 259:157-167, 2000. (C) 2000 Wiley-Liss, Inc.