Maternally-Activated Lineage Tracing ( Raeppli ) To Determine Anlagen Size in Drosophila

We used Raeppli , a sophisticated fluorescent lineage tracing system developed for Drosophila , to map cell clones beginning at the earliest possible stage in development. By expression of the ϕC31 Integrase (the final step in activating lineage marking) in nurse cells and oocytes, we reduced the methodological and biological variation in cell lineage analysis. We characterized the number of cells in fully-developed larval salivary glands, and thereby inferred the number of cells in embryonic anlage, the number of divisions during differentiation, and the variation in clonal behavior. This approach - novel for Raeppli - represents a powerful addition to lineage analysis in Drosophila .