THE FATE OF THE CNS MIDLINE PROGENITORS IN DROSOPHILA AS REVEALED BY A NEW METHOD FOR SINGLE-CELL LABELING

We present a new method for marking single cells and tracing their dev elopment through embryogenesis. Cells are labelled with a lipophilic f luorescent tracer (DiI) in their normal positions without impaling the ir membranes. The dye does not diffuse between cells but is transferre d to the progeny, disclosing their morphology in all detail. Behaviour of labelled cells can be observed in vivo (cell divisions, morphogene tic movements and differentiation). Following photoconversion of the d ye, fully differentiated clones can be analyzed in permanent preparati ons. We apply this method for cell lineage analysis of the embryonic D rosophila CNS. Here we describe the fate of the CNS midline cells. We present the complete lineages of these cells in the fully differentiat ed embryo and show that variability exists in segmental numbers of the midline progenitors as well as in the composition of their lineages,