Expression patterns of Notch1, Notch2, and Notch3 suggest multiple functional roles for the Notch-DSL signaling system during brain development.

The Notch-DSL signaling system consists of multiple receptors and ligands, and plays many roles in development. The function of Notch receptors and ligands in mammalian brain, however, is poorly understood. In the current study, we examined the expression patterns for three receptors of this system, Notch1, 2, and 3, in late embryonic and postnatal rat brain by in situ hybridization. The three receptors have overlapping but different patterns of expression. Messenger RNA for all three proteins is found in postnatal central nervous system (CNS) germinal zones and, in early postnatal life, within numerous cells throughout the CNS. Within zones of cellular proliferation of the postnatal brain, Notch1 mRNA is found in both the subventricular and the ventricular germinal zones, whereas Notch2 and Notch3 mRNAs are more highly localized to the ventricular zones. Both Notch1 and Notch3 mRNAs are expressed along the inner aspect of the dentate gyrus, a site of adult neurogenesis. Notch2 mRNA is expressed in the external granule cell layer of the developing cerebellum. In several brain areas, Notch1 and Notch2 mRNAs are relatively concentrated in white matter, whereas Notch3 mRNA is not. Neurosphere cultures (which contain CNS stem cells), purified astrocyte cultures, and striatal neuron-enriched cultures express Notch1 mRNA. However, in these latter cultures, Notch1 mRNA is produced by nestin-containing cells, rather than by postmitotic neurons. Taken together, these results support multiple roles for Notch1, 2, and 3 receptor activation during CNS development, particularly during gliogenesis.

Pescadillo, a novel cell cycle regulatory protein abnormally expressed in malignant cells.

Using a culture model of glial tumorigenesis, we identified a novel gene that was up-regulated in malignant mouse astrocytes following the loss of p53. The gene represents the murine homologue of pescadillo, an uncharacterized gene that is essential for embryonic development in zebrafish. Pescadillo is a strongly conserved gene containing unique structural motifs such as a BRCA1 C-terminal domain, clusters of acidic amino acids and consensus motifs for post-translational modification by SUMO-1. Pescadillo displayed a distinct spatial and temporal pattern of gene expression during brain development, being detected in neural progenitor cells and postmitotic neurons. Although it is not expressed in differentiated astrocytes in vivo, the pescadillo protein is dramatically elevated in malignant human astrocytomas. Yeast strains harboring temperature-sensitive mutations in the pescadillo gene were arrested in either G(1) or G(2) when grown in nonpermissive conditions, demonstrating that pescadillo is an essential gene in yeast and is required for cell cycle progression. Consistent with the latter finding, DNA synthesis was only observed in mammalian cells expressing the pescadillo protein. These results suggest that pescadillo plays a crucial role in cell proliferation and may be necessary for oncogenic transformation and tumor progression.