Article

An Epigenetic Role for Maternally Inherited piRNAs in Transposon Silencing

Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory (CSHL), 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA.
Science (Impact Factor: 33.61). 12/2008; 322(5906):1387-92. DOI: 10.1126/science.1165171
Source: PubMed

ABSTRACT

In plants and mammals, small RNAs indirectly mediate epigenetic inheritance by specifying cytosine methylation. We found that
small RNAs themselves serve as vectors for epigenetic information. Crosses between Drosophila strains that differ in the presence of a particular transposon can produce sterile progeny, a phenomenon called hybrid dysgenesis.
This phenotype manifests itself only if the transposon is paternally inherited, suggesting maternal transmission of a factor
that maintains fertility. In both P- and I-element–mediated hybrid dysgenesis models, daughters show a markedly different content of Piwi-interacting RNAs (piRNAs)
targeting each element, depending on their parents of origin. Such differences persist from fertilization through adulthood.
This indicates that maternally deposited piRNAs are important for mounting an effective silencing response and that a lack
of maternal piRNA inheritance underlies hybrid dysgenesis.

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    • "The relative levels of putative microRNAs and piRNAs change markedly as development progresses. piRNAs are highly abundant in the earliest stages of development , consistent with their maternal deposition (Brennecke et al. 2008). MicroRNA levels, on the other hand, are initially very low but gradually increase and account for nearly 30% of all small RNA reads in the late embryo. "
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    • "Because these embryos have no fully onset transcription (Vlassova et al. 1991; Pritchard and Schubiger 1996), their small RNAs and Piwi proteins are essentially the same of the maternal germ cells (Harris and Macdonald 2001; Megosh et al. 2006; Brennecke et al. 2008; Le Thomas et al. 2014). A similar scenario was found for D. melanogaster (Brennecke et al. 2008). At early embryogenesis, the maternally inherited piRNAs and piwi proteins could be leading elements in the process of defining heterochromatic domains (Sentmanat et al. 2013). "
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    • "et al., 2013; Siomi et al., 2011). In this view, Aub-bound, maternally deposited antisense piRNAs must initiate ping-pong amplification, leading to the accumulation of Ago3-bound sense piRNAs (Brennecke et al., 2008; Le Thomas et al., 2014). Pingpong amplification of Ago3-bound piRNAs would then serve to ensure a sufficient supply of guides for Piwi. "
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