Role of cell death in the development of the adult Drosophila optic lobe during metamorphosis. Hidenobu Tsujimura¹, Tatsuya Sudo¹, Yusuke Hara^1,2, Yu Togane¹, Hiromi Akagawa^1,2, Ayano Ishitsuka¹, Masashi Iwamura¹, Ryo Iizuka¹, Ayaka Tsutsumi¹. 1) Dept Dev Biol, Tokyo Univ Agric & Tech, Fuchu-si, Tokyo, Japan; 2) Dept Bio Pro Sci, Tokyo Univ of Agric & Tech, Fuchu-si, Tokyo, Japan.

   In the Drosophila optic lobe many cells die during development. We have found that the cell death is caspase-dependent apoptosis and mainly occurs in neurons during the formation of neural circuits. It is observed in some specific clusters of cells in the developing optic lobe and includes ecdysone-dependent and independent ones. However, physiological meaning of the cell death is remained to be defined. Here, to define the meaning, we analyzed by immunostaining the structure of optic lobes where the cell death was inhibited with p35, a baculovirus cell death inhibitor. p35 was overexpressed in neurons, glia or both of them and structural defect was examined. The structure of the optic lobe was almost the same as that in the wild type when p35 was overexpressed in glia. In contrast, many defects were observed at various structural levels when p35 was expressed in neurons. Most prominent ones were newly emerged abnormal nerve tracts and abnormal neurite lumps in the cortices that were surrounded by glia. We also observed defects in the separation and rearrangement of neuropils and loss and disorder of some columns in medulla neuropil . These results show that the cell death is essential for normal optic lobe development. Frequency of abnormal neurite lumps and nerve tracts reduced as development proceeded when p35 was expressed in neurons. However, the defects persisted into later stages when p35 was expressed both in neurons and glia. These facts suggest that glia may be involved in the removal of the abnormal structures and caspase activity in gia may be required for the removal.