Autophagy and apoptosis in insect cells during metamorphosis

During insect metamorphosis,degeneration or dissolution of larval tissues was involved in programmed cell death(PCD)including autophagy and apoptosis induced by ecdysteroids.Autophagy,which usually responds to hungry to avoid cell death,appears as a low-level Cvt vesicle and autophagosome to swallow and dissolve partial cytosol,protein aggregates and cellular organelles.PCD pathway is initiated by ecdysteroids and regulated by genetic cascade system during the period of insect metamorphosis.The initiation of PCD pathway by ecdysteroids turns the low-level normal autophagy to high-level one and triggers apoptosis at the same time,and leads to irreversible death.Subsequently larval tissues degenerate or dissolve completely.The most important discoveries of PCD in fruit fly Drosophila metamorphosis include:(1)In the molecular pathways of PI3KI-Tor and PI3KIII,high-level autophagy initiated by Atg1(autophagy-related protein 1)can induce apoptosis;(2)Transcription factors induced by ecdysteroids,including βFTZ-F1,E93,BR-C and E74A,can not only activate the apoptosis pathway,but also induce autophagy pathway.