Characterization of tissue specific expression of Notch-1 in human tissues.

Signaling through the Notch cell surface receptors is a highly conserved mechanism of cell fate specification. Notch signaling regulates proliferation, differentiation and cell death. In vertebrates, putative gene duplication has originated four Notch genes, Notch-1, -2, -3 and -4. They have been implicated in neurogenesis, hematopoiesis, T-cell development, vasculogenesis and brain cortical growth. We have investigated Notch-1 distribution in normal human tissues by immunohistochemistry and immunoblot. We detected widespread expression of Notch-1 cytoplasmatic staining, with different tissue distributions in the different organs examined. In particular, high expression of Notch-1 was detected in the intermediate suprabasal layers, but not in the dead cells at the extreme periphery of stratified epithelia. Moreover, a low/intermediate level of Notch-1 was observed in lymphocytes in several peripheral lymphoid tissues; in particular the germinal centers of lymph nodes showed the most abundant number of positive cells, which appeared to be centroblasts/immunoblasts based on nuclear morphology. Notch-1 participates in keratinocytes differentiation. We showed by Western blot analysis that Notch-1 level was clearly increased in HaCaT cells after Ca(++) addition and remained substantially elevated until late differentiation stages. These results suggest that Notch-1 may function in numerous cell types in processes beyond cell fate determination, such as neuronal plasticity, muscle hypertrophy, liver regeneration, and germinal center lymphopoiesis during the immune response.