THE USE OF PHOTOACTIVATABLE REAGENTS FOR THE STUDY OF CELL LINEAGE IN DROSOPHILA EMBRYOGENESIS

This chapter describes the use of photoactivatable lineage tracers in early Drosophila development. This technique involves the injection of a nuclear-targeted dextran reagent bearing caged fluorescein moieties into a precellularization embryo. All syncytial nuclei accumulate this nonfluorescent reagent and fluorescence is induced in nuclei, during or following cellularization, by a microbeam of light that stimulates photochemical uncaging. The fluorescent cell and its daughters can be identified either in the living embryo, offering the opportunity to follow the movements of cells during embryogenesis, or in fixed material allowing the positioning of clones with respect to patterns of gene expression. This photoactivatable tracer has several advantages over other cell marking techniques and is particularly suited to lineage studies in the embryo. The nuclear localization of the reagent permits single cells to be identified accurately in fields of adjoining, marked cells. The marking is precise in that the stage of the embryo and the particular cell that is marked are defined visually at the time of marking. Photoactivatable lineage tracers represent a major advance for clonal analysis in the early embryo and the study of cell movements. Any cell in the blastoderm can be marked, and the nuclear localization of the signal allows excellent resolution in identifying the daughters of individual cells. © 1994, Elsevier Science Publishers, B.V. All rights reserved.