Conservation of small RNA pathways in platypus
- Elizabeth P. Murchison1,
- Pouya Kheradpour2,
- Ravi Sachidanandam1,
- Carly Smith1,
- Emily Hodges1,
- Zhenyu Xuan1,
- Manolis Kellis2,3,
- Frank Grützner4,
- Alexander Stark2,3, and
- Gregory J. Hannon1,5
- 1 Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA;
- 2 Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
- 3 Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02141, USA;
- 4 Discipline of Genetics, School of Molecular & Biomedical Science, The University of Adelaide, Adelaide, 5005 SA, Australia
Abstract
Small RNA pathways play evolutionarily conserved roles in gene regulation and defense from parasitic nucleic acids. The character and expression patterns of small RNAs show conservation throughout animal lineages, but specific animal clades also show variations on these recurring themes, including species-specific small RNAs. The monotremes, with only platypus and four species of echidna as extant members, represent the basal branch of the mammalian lineage. Here, we examine the small RNA pathways of monotremes by deep sequencing of six platypus and echidna tissues. We find that highly conserved microRNA species display their signature tissue-specific expression patterns. In addition, we find a large rapidly evolving cluster of microRNAs on platypus chromosome X1, which is unique to monotremes. Platypus and echidna testes contain a robust Piwi-interacting (piRNA) system, which appears to be participating in ongoing transposon defense.
Footnotes
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↵5 Corresponding author.
↵5 E-mail hannon{at}cshl.edu; fax (516) 367-8874.
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[Supplemental material is available online at www.genome.org. The microRNA sequence data from this study have been submitted to miRBase under accession nos. MI0006658–MI0007078 (http://microrna.sanger.ac.uk/sequences/).
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Article published online before print. Article and publication date are at http://www.genome.org/cgi/doi/10.1101/gr.073056.107.
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- Received October 15, 2007.
- Accepted February 26, 2008.
- Copyright © 2008, Cold Spring Harbor Laboratory Press
