Differential expression of Notch1 and Notch2 in developing and adult mouse brain.
The Notch gene encodes a large transmembrane protein, and is required for the correct differentiation of both neural and non-neural tissues in Drosophila. Mammals have more than one Notch gene homolog, e.g. Notch1 and Notch2. Here, in order to determine the role of Notch genes in the mouse nervous system, we used in situ hybridization to study the expression of the Notch1 and -2 genes through mouse embryogenesis and into adulthood. The expression of Notch1 and Notch2 differed throughout development. Notch2 was expressed in the embryonic ventricular zone, the postnatal ependymal cells, and the choroid plexus throughout embryonic and postnatal development. Notch1 was also expressed in the ventricular zone between embryonic days 10 and 14, but its expression decreased gradually as embryos developed. The postnatal mouse brain strongly expressed Notch2, but not Notch1, in the granular cell layer of hippocampal dentate gyrus, where neurogenesis continues even in adult rodents. The most remarkable finding was the detection of a strong signal for Notch2 mRNA in two circumventricular organs: the subfornical organ and the area postrema. The receptor encoded by the Notch2 gene, which is located in these areas, may respond to unknown ligands in CSF. This putative receptor may participate in signal transduction by way of both neural and humoral links. These data suggest that Notch2, rather than Notch1, is related not only to development, but also to some postnatal functions of mouse central nervous system.