[Disordered development of Drosophila melanogaster embryos mosaic for the Notch gene]

Gene Notch codes for a transmembrane protein, which is involved in cell interactions: mutations in Notch locus result in differentiation of all cells of the ventral and anterodorsal ectoderm into neuroblasts. In order to examine interrelations between cells of the normal and mutant phenotype, mosaic embryos were obtained. Procephalic regions of Drosophila trunk were most strongly affected in the experimental, as well as in the control, embryos. In control mosaics, the absence of anterodorsal ectoderm was accompanied by a decrease in the size of epipharyngeal ganglion, whereas Notch mosaics, in contrast, showed the expansion of epipharyngeal ganglion over dorsal ectoderm up to the posterior end of the embryo. Differentiation abnormalities of cells of the ventral ectoderm in Notch mosaics were rarer. Generally, the results of our experiments lead to a hypothesis about the presence of a certain threshold in the proportion between Notch cells and wild-type cells in ventral ectoderm. When this threshold value is exceeded, all cells of ventral ectoderm differentiate into neuroblasts.