Autonomous and non-autonomous phenotypic expression of Notch mutant cells in Drosophila embryogenesis

Transplantation of single homozygous Notch ^- cells into the ventral neuroectoderm of Drosophila wild-type embryos reveals a non-autonomous behaviour of these cells. However, mitotic recombination events induced in heterozygous cells in imaginal discs lead to generation of homozygous Notch ^- cells which differentiate cell autonomously. We have tested various possible explanations for the non-autonomous behaviour of Notch mutant cells following transplantation. We confirm the previous results using different Notch alleles. Moreover, we find that increasing the number of wild-type Notch copies in a cell increases probability that it will take on an epidermal fate. However, single Notch mutant cells behave differently depending on whether they are placed in the ventral neuroectoderm, the procephalic neuroectoderm or the proctodeal anlage. Following transplantation into host embryos devoid of mesoderm, almost all single Notch mutant cells behave autonomously. These results suggest an influence of the mesoderm on ectodermal development. Finally, we provide further evidence that DELTA acts as the signal source in lateral inhibition.