The early development of mesothoracic compartments in Drosophila

The results from three methods of studying the cell lineage of early Drosophila development are reported: clonal analysis, the Minute technique, and gynandromorph fate mapping. We conclude that by about one division after blastoderm anterior and posterior groups of cells in the mesothorax are separated, as are the groups of cells that generate different segments. Clones produced by irradiation of eggs aged 4 ± 2 hr do cross from wing to leg, so that these two discs share a common origin until at least two divisions after blastoderm. The number of epidermal cells in the wing disc of the newly hatched larva is estimated at about 20 cells. Gynandromorph fate mapping is discussed in detail. It is concluded that sturt distances between landmarks are not only determined by distance apart of their progenitor cells at blastoderm, but are strongly dependent on compartmentalisation and other aspects of postembryonic development. The consequences of this are discussed. We discuss the evidence that anterior and posterior groups of wing cells may be adjacent at blastoderm.