DROSOPHILA MITOTIC DOMAIN BOUNDARIES AS CELL FATE BOUNDARIES

Fate determination in Drosophila embryos is evidenced by the appearanc e of mitotic domains. To identify fate or fates of cells, individual c ells 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 o f 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 expressi on in Xenopus embryos. Thus, photoactivated gene expression is a versa tile tool for spatiotemporal control of gene expression.