Drosophila embryonic neurogenesis occurs at the blastoderm stage in the neuroectoderm. Pre-patterning factors initiate transcription of proneural genes at the expanse of neuroectoderm, which are expressed almost evenly in clusters of cells in the beginning. Later, the Notch signaling involves in to fine-tune expression of proneural genes and determines only one cell to adopt neuroblast fate in each cluster. The chosen cell with the highest proneural genes expression would single out and constrict apical area to delaminate into the interior of the embryo. But the exact dynamics of proneural genes expression during neurogenesis are not well known due to lack of live imaging tracking marker.

Because of the fast turnover rate of transcription factor and slow maturation of most flu...[ Read more ]

Drosophila embryonic neurogenesis occurs at the blastoderm stage in the neuroectoderm. Pre-patterning factors initiate transcription of proneural genes at the expanse of neuroectoderm, which are expressed almost evenly in clusters of cells in the beginning. Later, the Notch signaling involves in to fine-tune expression of proneural genes and determines only one cell to adopt neuroblast fate in each cluster. The chosen cell with the highest proneural genes expression would single out and constrict apical area to delaminate into the interior of the embryo. But the exact dynamics of proneural genes expression during neurogenesis are not well known due to lack of live imaging tracking marker.

Because of the fast turnover rate of transcription factor and slow maturation of most fluorescent proteins, the attempts to visualize these proneural factors always fail in vivo. To circumvent this problem, here I use a chemical tag reporter system, Halotag and its ligand, to reveal the dynamics of proneural genes expression in the early live embryo. Under control of the promoter from one of the proneural genes, achaete, cluster pattern of ac expression is detected in the anterior side of each segment. Quantification data indicate that the ac expression is elevated in both delaminating neuroblasts and neighboring cells. But the intensity increases much faster in neuroblast than that in neighboring cells, reflecting the function of lateral inhibition mediated by Notch signaling. Meanwhile, the apical area of the cell with the highest Halotag intensity is reduced gradually, suggesting both the fate and morphology of neuroblast are consolidated gradually over time. When Notch signaling is disrupted, all cells constrict their apical region and Halotag intensity increases with a similar speed among all cells. In contrast, the increase of Halotag is crippled in all cells when NICD is ectopically overexpressed. More interestingly, when the morphogenesis of neuroblast is blocked by Cytochalasin D, the dynamics of Halotag expression are not altered and the cell with highest proneural gene expression still adopts neuroblast fate, indicating the fate adoption is independent of morphogenesis during neurogenesis in early Drosophila embryo. Therefore, this study provides new insights into the dynamic regulation of proneural genes and may unleash the power of chemical tags in live samples.