Drosophila mitotic domain boundaries as cell fate boundaries.

Fate determination in Drosophila embryos is evidenced by the appearance of mitotic domains. To identify fate or fates of cells, individual cells in mitotic domains 2, 8, and 15 were marked and monitored through development. Comparison of the different fates indicated that domain boundaries are cell fate boundaries. Cells were marked by expression of GAL4-dependent transgenes after photoactivation of a caged GAL4VP16 analog that had its DNA binding activity inhibited with a photolabile blocking reagent. Caged GAL4VP16 was also used to induce gene expression in Xenopus embryos. Thus, photoactivated gene expression is a versatile tool for spatiotemporal control of gene expression.