Spatio-temporal pattern of programmed cell death in the developing Drosophila optic lobe.

A large number of cells die via programmed cell death during the normal development of the Drosophila optic lobe. In this study, we report the precise spatial and temporal pattern of cell death in this organ. Cell death in the developing optic lobe occurs in two distinct phases. The first phase extends from the start of metamorphosis to the mid-pupal stage. During this phase, a large number of cells die in the optic lobe as a whole, with a peak of cell death at an early pupal stage in the lamina and medulla cortices and the region of the T2/T3/C neurons, and a smaller number of dead cells observed in the lobula plate cortex. The second phase extends from the mid-pupal stage to eclosion. Throughout this period, a small number of dying cells can be observed, with a small peak at a late pupal stage. Most of the dying cells are neurons. During the first phase, dying cells are distributed in specific patterns in cortices. The lamina cortex contains two distinct clusters of dying cells; the medulla cortex, four clusters; the lobula plate cortex, one cluster; and the region of the T2/T3/C neurons, one cluster. Many of the clusters maintain their distinct positions in the optic lobe but others extend the region they cover during development. The presence of distinct clusters of dying cells at different phases suggests that distinct mechanisms control cell death during different stages of optic lobe development in Drosophila.