Question: Are piRNAs involved in gene silencing?

Context:
In Drosophila ovaries, the nuclear Piwi protein is required for transcriptional silencing of transposons, though the precise mechanisms by which this occurs are unknown.
Here we show that the CG9754 protein is a component of Piwi complexes that functions downstream of Piwi and its binding partner, Asterix, in transcriptional silencing. Enforced tethering of CG9754 to nascent messenger RNA transcripts causes cotranscriptional silencing of the source locus and the deposition of repressive chromatin marks.
We have named CG9754 "Panoramix," and we propose that this protein could act as an adaptor, scaffolding interactions between the piRNA pathway and the general silencing machinery that it recruits to enforce transcriptional repression.
piRNA-guided slicing of transposon transcripts enforces their transcriptional silencing via specifying the nuclear piRNA repertoire
Caenorhabditis elegans piRNAs interact with both transposon and nontransposon mRNAs to initiate sustained silencing via the RNAi pathway.
To assess the dysregulation of gene silencing caused by lack of piRNAs, we restored RNA silencing in RNAi-defective animals in the presence or absence of piRNAs.
Thus, by reanimating RNAi, we uncovered a role for piRNAs in protecting essential genes from RNA silencing.
In different organisms, small RNAs were shown to be implicated in the posttranscriptional degradation of mRNA and/or transcriptional repression of the homologous locus. In Drosophila, the mechanism of piRNA-mediated silencing is still far from being understood
Analyses of piRNA-mediated transcriptional transposon silencing in Drosophila
Transcriptional silencing implies a piRNA-mediated formation of repressive chromatin which diminishes the transcriptional capacity of the target locus.
In mice, piRNA-guided transposon repression correlates with establishment of CpG DNA methylation on their sequences, yet the mechanism and the spectrum of genomic targets of piRNA silencing are unknown
Using a candidate gene KD-approach, we identified differences in the spatio-temporal requirements of the piRNA pathway components for piRNA-mediated silencing.
Spatio-temporal requirements for transposable element piRNA-mediated silencing during Drosophila oogenesis
In contrast, piRNA-mediated silencing is strong in germline stem cells in which TE mobilization is tightly repressed ensuring the continued production of viable germline cysts.
Piwi induces piRNA-guided transcriptional silencing and establishment of a repressive chromatin state.
In germ cells, early embryos, and stem cells of animals, PIWI-interacting RNAs (piRNAs) have an important role in silencing retrotransposons, which are vicious genomic parasites, through transcriptional and post-transcriptional mechanisms.
Our results show that the piRNA pathway can be used as a tool for sequence-specific gene silencing in germ cells and support the idea that the piRNA generating regions serve as traps for retrotransposons, enabling the host cell to generate piRNAs against active retrotransposons.
 Our observations confirm the pivotal role of piRNA-mediated silencing in defending the genome against selfish transposition, yet also suggest limits to the optimization of host genome defense.
Analysis of piRNA-mediated silencing of active TEs in Drosophila melanogaster suggests limits on the evolution of host genome defense
The Piwi-interacting RNA (piRNA) pathway defends animal genomes against the harmful consequences of transposable element (TE) infection by imposing small-RNA-mediated silencing.
A novel organelle, the piNG-body, in the nuage of Drosophila male germ cells is associated with piRNA-mediated gene silencing.
Proteins of the PIWI subfamily Aub and AGO3 associated with the germline-specific perinuclear granules (nuage) are involved in the silencing of retrotransposons and other selfish repetitive elements in the Drosophila genome. 
Telomeric retroelements HeT-A, TART and TAHRE, which are involved in telomere maintenance in Drosophila, are also the targets of piRNA-mediated silencing
Mechanism of the piRNA-mediated silencing of Drosophila telomeric retrotransposons.
Gene silencing mechanisms mediated by Aubergine piRNA complexes in Drosophila male gonad.
The epigenetic trans-silencing effect in Drosophila involves maternally-transmitted small RNAs whose production depends on the piRNA pathway and HP1.
Here, we show that mutations in squash and zucchini, which are involved in the piwi-interacting RNA (piRNA) silencing pathway, strongly affect TSE
MVH in piRNA processing and gene silencing of retrotransposons
piRNA-mediated silencing in Drosophila germlines.
These have shed light not only on the molecular mechanisms of gene silencing mediated by piRNAs and PIWI proteins, but also on their intriguing relationship with cellular genes that have been shown to be important for gametogenesis and fertility.
The most abundant piRNAs were those corresponding to antisense transcripts of Suppressor of Stellate [Su(Ste)] genes known to be involved in Stellate gene silencing
To determine the capacity of piRNA-mediated silencing, we introduced reporter genes into Drosophila OSS cells, which express microRNAs (miRNAs) and piRNAs, and compared the Piwi pathway to the Argonaute pathway in gene regulation
PIWI-interacting small non-coding RNAs (piRNAs) are genetic and epigenetic regulatory factors in germline cells, where they maintain genome stability, are involved in RNA silencing and regulate gene expression
The piNG-body contains ribonucleoprotein complexes involved in piRNA-silencing of genome repeats including transposons in premeiotic spermatocytes with aid of short piRNAs
Our results show that the piRNA pathway can be used as a tool for sequence-specific gene silencing in germ cells and support the idea that the piRNA generating regions serve as traps for retrotransposons, enabling the host cell to generate piRNAs against active retrotransposons
Recent studies have revealed not only the biogenesis of piRNAs and their roles in transposon silencing, but also the function of the Piwi-piRNA pathway in epigenetic and post-transcriptional regulation of gene expression
A growing number of studies on piRNAs have investigated piRNA-mediated gene silencing, including piRNA biogenesis
These have shed light not only on the molecular mechanisms of gene silencing mediated by piRNAs and PIWI proteins, but also on their intriguing relationship with cellular genes that have been shown to be important for gametogenesis and fertility
Telomeric retroelements HeT-A, TART and TAHRE, which are involved in telomere maintenance in Drosophila, are also the targets of piRNA-mediated silencing. 
MVH in piRNA processing and gene silencing of retrotransposons.
To determine the capacity of piRNA-mediated silencing, we introduced reporter genes into Drosophila OSS cells, which express microRNAs (miRNAs) and piRNAs, and compared the Piwi pathway to the Argonaute pathway in gene regulation. 
Therefore piRNA-mediated transcriptional mode of silencing is involved in the control of retrotransposon expression in the Drosophila germline.
Panoramix enforces piRNA-dependent cotranscriptional silencing.
The most abundant piRNAs were those corresponding to antisense transcripts of Suppressor of Stellate [Su(Ste)] genes known to be involved in Stellate gene silencing.
Our results indicate that piRNAs are involved in a posttranscriptional gene-silencing mechanism resulting in RNA nuclear accumulation.

Answer: Piwi induces piRNA-guided transcriptional silencing and establishment of a repressive chromatin state. piRNA-guided slicing of transposon transcripts enforces their transcriptional silencing via specifying the nuclear piRNA repertoire. Transcriptional silencing implies a piRNA-mediated formation of repressive chromatin which diminishes the transcriptional capacity of the target locus.
Exact answer: yes