Programmed cell death during the adult midline formation in Drosophila melanogaster

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In Drosophila melanogaster, a midline formation for adult epidermis proceed during metamorphosis. I examined the involvement of the cell death during the midline formation.A replacement of epidermis from larval cells to adult ones was examined at the abdominal region during metamorphosis. The larval epidermal cells migrated from dorsal to midline and were detached from the cuticle at the midline between 24 to 36 hr APF. In vivo observation of the elimination process of the larval cells, using the gal4/UAS-GFP system, showed that the nucleus of the larval cells was fragmented and that the apoptotic bodies appeared. Thus, the larval epidermal cells would die through the apoptotic processes. The ectopic expression of anti-apoptotic gene, p35, whose products inhibit the activity of the caspases that proceed the apoptosis, in the larval epidermal cells during metamorphosis prevented the death of them and caused an adult fly having the larval epidermis at the midline. In the hid mutants, inhibition of cell death occurred in the larval epidermal cells, which also caused the defect in the adult midline. Thus, cell death in the larval epidermal cells is necessary for the midline formation.At the thoracic region, adult epidermal cells fuse to make midline during early pupa. Our studies using TUNEL staining showed that some cells at the midline die in this process. In the reaper-lacZ flies, the expression of marker gene was observed at the midline. Also, at the same region, I found that the dpp gene was expressed. To examine whether the dpp signal controls the expression of reaper gene. I analyzed the effect of mutation of dpp-related genes on the expression of reaper. However, the reaper expression was not changed in the mutants, suggesting other factor that control the cell death during the midline formation.