title: 20-hydroxyecdysone upregulates apoptotic genes and induces apoptosis in the Bombyx fat body.
abstract: During insect metamorphosis, obsolete larval tissues are removed by programed cell death (PCD), mainly apoptosis and autophagy, which is directed by the molting hormone, 20-hydroxyecdysone (20E) and the 20E-triggered transcriptional cascade. Here, we investigated how 20E regulates apoptosis at the transcriptional level in the fat body of the silkworm, Bombyx mori. As detected by TdT-mediated dUTP Nick-End Labeling (TUNEL), apoptosis weakly occurred during the fourth larval molting, decreased to undetected levels during the early fifth instar, and gradually increased from day 4 of fifth instar to the wandering stage to the prepupal stage. Meanwhile, as determined by quantitative real-time PCR, eight genes involved in apoptosis, including Apaf-1, Nedd2 like1, Nedd2 like2, ICE1, ICE3, ICE5, Arp, and IAP, were highly expressed during molting and pupation, when the 20E titer is high. Injection of 20E into day 2 of fifth instar larvae significantly induced apoptosis and upregulated apoptotic genes after 6 h of treatment, and in vitro treatment of larval fat body tissues with 20E upregulated all the eight apoptotic genes. Moreover, RNAi knockdown of USP, a component of the 20E receptor complex EcR-USP, at the early-wandering stage reduced apoptosis and downregulated apoptotic genes after 24 h of treatment. Taken together, we infer that 20E upregulates apoptotic genes and thus induces apoptosis in the Bombyx fat body during larval molting and the larval-pupal transition.
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China. tianling80@yahoo.com.cn
authors.forename: Ling
authors.initials: L
authors.lastname: Tian
authors.forename: Shumin
authors.initials: S
authors.lastname: Liu
authors.forename: Hanhan
authors.initials: H
authors.lastname: Liu
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
mesh_terms: D000818:Animals; D017209:Apoptosis; D012831:Bombyx / Q000235:genetics / Q000378:metabolism*; D004441:Ecdysterone / Q000378:metabolism*; D005216:Fat Body / Q000378:metabolism*; D005786:Gene Expression Regulation; D019476:Insect Proteins / Q000378:metabolism*; D007814:Larva / Q000378:metabolism; D018978:Molting; D034622:RNA Interference
chemical_list: D019476:Insect Proteins; D004441:Ecdysterone