Piwi-Interacting RNAs...Piwi Discovery Piwi-/- Lin et al, Development, 1997WT • PIWI:...
Transcript of Piwi-Interacting RNAs...Piwi Discovery Piwi-/- Lin et al, Development, 1997WT • PIWI:...
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Piwi-Interacting RNAs
Molly Thomas5/6/2009
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Piwi Discovery
Piwi-/-
Lin et al, Development, 1997
WT
• PIWI: P-element-Induced WImpy testes
• Comprises the Piwi clade of Argonaute proteins
Ago-/-
Bohmert et al, EMBO Journal, 1998
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Meister and Höck, Genome Biol, 2008
Ago
Piwi
N L1 PAZ MidL2 Piwi
3’ Binding Site
m7G Cap Binding 5’ MP Binding
Catalytic Slicer Activity
Piwi Discovery
• PIWI: P-element-Induced WImpy testes
• Comprises the Piwi clade of Argonaute proteins
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Loss of Murine Piwi Homologues Leads to Spermatogenic Arrest
/Miwi-2
Narry Kim, Genes and Development, 2006
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Loss of Murine Piwi Homologues Leads to Spermatogenic Arrest
/Miwi-2
Narry Kim, Genes and Development, 2006
Mili
Kuramochi-Miyagawa, Development, 2004
Miwi
Deng and Lin, Dev Cell, 2002
+/- -/-
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piRNA Discovery
Watanabe et al, Genes and Development,
2006
Grivna et al, Genes and
Development, 2006
Girard et al, Nature, 2006
Aravan et al, Nature, 2006
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piRNA Discovery
Aravan et al, Nature, 2006
Highlyconserved strand bias
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Aravan et al, Nature, 2006
2 piRNA Populations in Mammals??
Aravan et al, Science, 2007
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Pachytene piRNAPre-pachytene piRNA
piR-1Chromosome 7 Pre-pachytene Cluster
Hen1 Hen1
Mili, Miwi-2(26-28 bp)
Miwi(29-31)
Reverse Complement
Rep
eat
Elem
ents
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Piwi/Aubergine
U
A3’ 5’
5’ 3’
3’ Exonuclease?Squash?
Zuchinni?
Ago3
A
Ago3
A
U3’ 5’
3’ Exonuclease?
Piwi/Aubergine
U5’ 3’
piRNA 1º Transcript
Target Transcript(i.e. repeat elements)
Ping-Pong Model of (Pre-Pachytene) piRNA Biogenesis
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piRNA Functions and Mechanisms
• Pre-pachytene: Silence Transposable Elements
• Miwi-2 and Mili
• IAP, LINE, SINE, LTR
• May require Piwi binding to heterochromatin (i.e. via HP1a)
• Pachytene: unknown
• Miwi associates with polysome fractions
• Miwi can bind translationally-inactive mRNAs
Miwi
Grivna et al, PNAS, 2006
Mili and Miwi-2 -/-
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A Role for piRNAs in Human Disease?
• Hiwi is overexpressed in testicular seminomas
• Expression of Hiwi in gastric and pancreatic cancers is positively correlated with cell proliferation
Qiao et al, Oncogene, 2002
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Grimson et al, Nature, 2008
Type 1(Pachytene) and Type 2 (pre-pachytene) piRNAs are Well-Conserved in Early Metazoans
Nematostella Amphimedon
(2) (2)
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Conclusions• piRNAs are a class of 24-30 nt small RNAs that
associate with PIWI proteins
• piRNAs are expressed predominantly in the male germline
• They are transcribed from conserved clusters into long single-stranded precursors
• There are at least 2 major types of piRNAs:
• Type 1 (pachytene): no known function
• Type 2 (pre-pachytene): protect genome from transposable elements