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Zygotic amplification of secondary piRNAs during silkworm embryogenesis

Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
RNA (Impact Factor: 4.62). 07/2011; 17(7):1401-7. DOI: 10.1261/rna.2709411
Source: PubMed

ABSTRACT PIWI-interacting RNAs (piRNAs) are 23-30-nucleotide-long small RNAs that act as sequence-specific silencers of transposable elements in animal gonads. In flies, genetics and deep sequencing data have led to a hypothesis for piRNA biogenesis called the ping-pong cycle, where antisense primary piRNAs initiate an amplification loop to generate sense secondary piRNAs. However, to date, the process of the ping-pong cycle has never been monitored at work. Here, by large-scale profiling of piRNAs from silkworm ovary and embryos of different developmental stages, we demonstrate that maternally inherited antisense-biased piRNAs trigger acute amplification of secondary sense piRNA production in zygotes, at a time coinciding with zygotic transcription of sense transposon mRNAs. These results provide on-site evidence for the ping-pong cycle.

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Available from: Shinpei Kawaoka, Aug 27, 2015
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    • "The sequence length distribution in the combined data set showed two peaks, one around 21–22 nt, and the other around 25–27 nt, which is consistent with studies in Bombyx mori (Jagadeeswaran et al., 2010) and Manduca sexta (Zhang et al., 2012). The peak at 25–27 nt probably corresponds to piRNAs, which act as sequencespecific silencers of transposable elements in many organisms but are completely different from miRNAs and their biogenesis is relatively unknown (Kawaoka et al., 2011). "
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    • "The ping-pong cycle generates characteristic cleavage specific piRNA sequence signatures [14] [20] in this manner, piRNAs whose targets are the TE transcripts show a bias for uridine at the 5′ end (5U), whereas the piRNA sequences generated from TE cleavage show a bias for nucleotide adenosine at position 10 (10A) [14] [20]. These characteristics have been conserved in such diverse organisms as the mouse, Drosophila, zebrafish and silkworm [9] [10] [22] [23]. Mutated PIWI family genes have been related to severe defects in male fertility [24] [25], on the contrary, female fertility was noticed to be unaffected by PIWI protein inactivation [24] [25]. "
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    • "The ping-pong cycle generates characteristic cleavage specific piRNA sequence signatures [14] [20] in this manner, piRNAs whose targets are the TE transcripts show a bias for uridine at the 5′ end (5U), whereas the piRNA sequences generated from TE cleavage show a bias for nucleotide adenosine at position 10 (10A) [14] [20]. These characteristics have been conserved in such diverse organisms as the mouse, Drosophila, zebrafish and silkworm [9] [10] [22] [23]. Mutated PIWI family genes have been related to severe defects in male fertility [24] [25], on the contrary, female fertility was noticed to be unaffected by PIWI protein inactivation [24] [25]. "
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