mDll1 and mDll3 expression in the developing mouse brain:: Role in the establishment of the early cortex

The Delta/Notch signalling system is involved in several developmental processes. During fly neurogenesis, Delta expression defines the fate of neuronal precursors and inhibits neighboring Notch-expressing cells from acquiring a neural fate, a process known as lateral inhibition. In vertebrates, recent evidence demonstrates that Notch activation can positively determine cell fate and affect neuronal process extension. Nevertheless, Delta-like expression patterns during brain development are relatively unknown. Using a transgenic mouse, which expresses LacZ under the mDII1 promoter, we show by immunofluorescence that in the developing telencephalon mDII1 is expressed in undifferentiated cells in close contact with radial glial cells. Based on in situ hybridization data on mDII1 and mDII3 mRNA expression and on the immunohistochemical detection of beta -galactosidase in the DII1-lacZ transgenic mouse, we suggest that mDII1 and mDII3 are involved in the establishment of the early cortical plate and that mDII1-expressing cells are in close contact with radial glial cells, thereby modulating the latter population, which is known to express Notch1, Furthermore, we suggest that the decrease in mDII1 mRNA found toward the end of gestation could be related, first, to the slowing of neurogenesis and, second, to the differentiation of the radial glial cell population into astrocytes. (C) 2001 Wiley-Liss, Inc.