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19 Cards in this Set
- Front
- Back
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Apoptotic mediators in Drosophila: |
- same as C. elegans - has regulators, adaptors and initiator/effector caspases |
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What are the pro-apoptotic regulators of apoptosis in Drosophila? |
- HID (associated with the mitochondria), REAPER and GRIM - dont have mammalian homologues |
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What are the anti-apoptotic regulators of apoptosis in Drosophila? |
- BUFFY - homologue of ced9/BCL-2; possesses BH1, BH2 and BH3 domains - DIAP-1, DIAP-2, Deterin - inhibit caspases; DIAP1 can also bind to HID, REAPER and GRIM |
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What is the key adaptor protein in Drosophila? |
- DARK - homologue of ced4 in C. elegans and Apaf-1 in humans - possesses domains for binding cytochrome c - central to Drosophila apoptosome formation = complex of DARK, cytochrome c and initiator caspases DREDD and DRONC |
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What kind of signals trigger apoptosis? |
- ecdysone (metamorphosis) - radiation - developmental defects - oxidative stress |
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What are the steps of apoptosis in Drosophila? |
- Presence of Reaper, HID and GRIM (RHG) antagonises the action of DIAP1 to release DRONC - initiator caspase DRONC is activated by binding (D)ARK that activates effector caspase DRICE leading to apoptosis |
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What are the steps of apoptosis in Drosophila and C. elegans (image) |
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How is the apoptosome complex formed in drosophila? |
- DARK exists as inactive monomer - activated by the release of cytochrome C - DARK or cytochrome c release is opposed by BUFFY - eight DARK molecules interact to form a wheel-like apoptosome - binds to pro-caspase - DRONC facilitating its activation |
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When is autophagy used? |
- cell survival mechanism in starving cells (cannibalism of own organelles for energy; regulated by Atg gene and class III PI3-kin) - degradation of old/damaged cellular components - turnover of organelles (mitochondria) or of damaged proteins - Role in cell degradation in PCD |
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What is the role of autophagy in PCD? |
- similar to starvation induced autophagy - autophagic cell death (ACD) regulation can be influenced by caspase activity - often seen alongside apoptosis (presence of autophagic vacuoles) - seen in mammals but very common in amphibians and insects - there is no phagocyte involvement |
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What does loss of Atg result in? |
- incomplete cell degradation during CD |
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PCD is an important step in metamorphosis. What hormones regulate the processes? |
- Regulatory hormones - Neurohormones (PTTH)(stimulates production of ecdysone) - Effector hormones - 20-hydrocyecdysone - (by prothoracic gland) stimulates gene expression in pulses, initiates molt and metamorphosis - Juvenile hormone - secreted by corpora allata; prevents ecdysone-induced gene expression that promotes pupal formation |
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Interplay between exdysone and juvenile hormone regulates molting and metamorphosis (image) |
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How does Ecdysone work? |
- by binding to nuclear receptor (EcR), the latter acting as a ligand activated TF - EcR forms heterodimer with ultraspiracle protein (USP), the insect homologue of RXR |
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How are genes activated by 20-hydroxyecdysone via the EcR TF? |
- polytene chromosomes (best seen in salivary gland cells) - regions of it puff out during molting and metamorphosis - indicates regions of DNA being trasncribed - EcR induce early genes and repress late genes (some early proteins induce late genes) |
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In Drosophila, ecdysone triggers metamorphosis leading to: |
- Destruction of larval midgut and anterior muscles - Elimination of salivary glands - remodelling of CNS - morphogenesis and differentiation of adult structures |
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What are the biochemical features of apoptosis and autophagy cell death in salivary glands? |
- Apoptosis - Elevated expression of HID, REAPER and GRIM, increased caspase activity, DNA fragmentation - ACD - autophagic vacuoles in cytoplasm, accumulation of acid phosphatase |
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What happens to salivary glands mutant for DARK? |
- defective histolysis (decay of organic tissue) |
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How does phagocytosis occur in Drosophila? |
- by macrophages - they express croquemort (crq) receptor - scavenger receptor - crq expression increased in salivary glands piror to PCD |
