title: Conservation of small RNA pathways in platypus.
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.
authors.affiliation: Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA.
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Murchison
authors.forename: Pouya
authors.initials: P
authors.lastname: Kheradpour
authors.forename: Ravi
authors.initials: R
authors.lastname: Sachidanandam
authors.forename: Carly
authors.initials: C
authors.lastname: Smith
authors.forename: Emily
authors.initials: E
authors.lastname: Hodges
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Xuan
authors.forename: Manolis
authors.initials: M
authors.lastname: Kellis
authors.forename: Frank
authors.initials: F
authors.lastname: Grützner
authors.forename: Alexander
authors.initials: A
authors.lastname: Stark
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Hannon
mesh_terms: D000818:Animals; D001483:Base Sequence; D019143:Evolution, Molecular; D008297:Male; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010987:Platypus / Q000235:genetics*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014960:X Chromosome
chemical_list: D035683:MicroRNAs; D034741:RNA, Small Interfering