ABSTRACT: piRNAs are a novel class of small noncoding RNAs that were recently identified in animal germ cells. This class of small noncoding RNAs is specifically associated with an evolutionarily conserved PIWI family proteins, which belong to the germline-specific members of the Argonaute protein family and are indispensable to germline development in animals. The PIWI/piRNA pathway has been deemed as an innate immune system that prevents mobile genetic elements from destabilizing DNA and that protects genome integrity in animal germ cells. By ribosome profiling using Miwi-null testes, we identified a group of ~600 mRNAs as likely direct piRNA targets for translational regulation in mouse spermatids. These results suggest that the mouse PIWI (MIWI)/piRNA is responsible for activating translation of a subset of spermiogenic mRNAs to coordinate with morphological transformation into elongated spermatids.
Project description:Germ cells employ elaborate mechanisms to maintain and protect their genetic material, and also to regulate gene expression during the complex differentiation process of gametogenesis. Piwi proteins, a subclade of the Argonaute family, are expressed mainly in the germline and bind piRNAs, a novel and diverse class of small RNAs whose biogenesis and putative functions are still largely elusive. We employed High Throughput Sequencing after Crosslinking and Immunoprecipitation (HITS-CLIP) coupled with RNA-Seq to characterize the genome-wide target RNA repertoire of Mili and Miwi, two mouse Piwi proteins. Our analysis outlines a model for primary piRNA biogenesis in postnatal mouse and indicates that piRNAs do not mediate target RNA recognition, but rather are the end products of RNA processing. Moreover, we identify a set of mRNAs essential for spermiogenesis that are bound and regulated by Miwi, directly implicating Piwi proteins in the control of gene expression at key time points of spermiogenesis. HITS-CLIP (High Throughput Sequencing after Crosslinking and Immunoprecipitation) experiments targeting two mouse Piwi proteins Mili and Miwi.
Project description:Piwi-interacting small RNAs (piRNAs) of fetal prospermatogonia of mice have been strongly implicated in transposon control. In contrast, little is known about biogenesis and function of abundant piRNAs from adult testes expressed in late spermatocytes and round spermatids. These so-called "pachytene" piRNAs are processed from long non-coding piRNA precursors and have no defined RNA targets in the transcriptome even though their binding partner Piwi, MIWI, is essential for spermiogenesis and fertility. Here we report that 129SvJae mice lacking Maelstrom (MAEL), a conserved piRNA pathway protein, exhibit spermiogenic arrest with defects in acrosome and flagellum formation. Further analysis revealed MAEL association with RNPs containing MIWI, TDRD6, and processed intermediates of pachytene piRNA precursors of various length. Loss of MAEL causes a 10-fold drop in pachytene piRNA levels but an increase in piRNAs from abundantly expressed mRNAs. These results suggest a MAEL-dependent mechanism for the selective processing of pachytene piRNA precursor into piRNAs. Strikingly, ribosome profiling of Mael-null testes revealed that reduced piRNA production is accompanied by reduced translation of over 800 spermiogenic mRNAs including those encoding acrosome and flagellum proteins. In light of recent reports of piRNA-independent protection of translationally repressed mRNPs by MIWI and piRNA-dependent turnover of MIWI, we propose that pachytene piRNAs function by controlling the availably of MIWI for the translational repression of spermiogenic mRNAs. piRNA sequencing, RNA immunoprecipitation, and expression measurements (RNA-Seq and ribosome profiling) in wild-type and Mael -/- testes
Project description:Piwi-interacting small RNAs (piRNAs) of fetal prospermatogonia of mice have been strongly implicated in transposon control. In contrast, little is known about biogenesis and function of abundant piRNAs from adult testes expressed in late spermatocytes and round spermatids. These so-called "pachytene" piRNAs are processed from long non-coding piRNA precursors and have no defined RNA targets in the transcriptome even though their binding partner Piwi, MIWI, is essential for spermiogenesis and fertility. Here we report that 129SvJae mice lacking Maelstrom (MAEL), a conserved piRNA pathway protein, exhibit spermiogenic arrest with defects in acrosome and flagellum formation. Further analysis revealed MAEL association with RNPs containing MIWI, TDRD6, and processed intermediates of pachytene piRNA precursors of various length. Loss of MAEL causes a 10-fold drop in pachytene piRNA levels but an increase in piRNAs from abundantly expressed mRNAs. These results suggest a MAEL-dependent mechanism for the selective processing of pachytene piRNA precursor into piRNAs. Strikingly, ribosome profiling of Mael-null testes revealed that reduced piRNA production is accompanied by reduced translation of over 800 spermiogenic mRNAs including those encoding acrosome and flagellum proteins. In light of recent reports of piRNA-independent protection of translationally repressed mRNPs by MIWI and piRNA-dependent turnover of MIWI, we propose that pachytene piRNAs function by controlling the availably of MIWI for the translational repression of spermiogenic mRNAs.
Project description:Germ cells employ elaborate mechanisms to maintain and protect their genetic material, and also to regulate gene expression during the complex differentiation process of gametogenesis. Piwi proteins, a subclade of the Argonaute family, are expressed mainly in the germline and bind piRNAs, a novel and diverse class of small RNAs whose biogenesis and putative functions are still largely elusive. We employed High Throughput Sequencing after Crosslinking and Immunoprecipitation (HITS-CLIP) coupled with RNA-Seq to characterize the genome-wide target RNA repertoire of Mili and Miwi, two mouse Piwi proteins. Our analysis outlines a model for primary piRNA biogenesis in postnatal mouse and indicates that piRNAs do not mediate target RNA recognition, but rather are the end products of RNA processing. Moreover, we identify a set of mRNAs essential for spermiogenesis that are bound and regulated by Miwi, directly implicating Piwi proteins in the control of gene expression at key time points of spermiogenesis.
Project description:Germ cells employ elaborate mechanisms to maintain and protect their genetic material, and also to regulate gene expression during the complex differentiation process of gametogenesis. Piwi proteins, a subclade of the Argonaute family, are expressed mainly in the germline and bind piRNAs, a novel and diverse class of small RNAs whose biogenesis and putative functions are still largely elusive. We employed High Throughput Sequencing after Crosslinking and Immunoprecipitation (HITS-CLIP) coupled with RNA-Seq to characterize the genome-wide target RNA repertoire of Mili and Miwi, two mouse Piwi proteins. Our analysis outlines a model for primary piRNA biogenesis in postnatal mouse and indicates that piRNAs do not mediate target RNA recognition, but rather are the end products of RNA processing. Moreover, we identify a set of mRNAs essential for spermiogenesis that are bound and regulated by Miwi, directly implicating Piwi proteins in the control of gene expression at key time points of spermiogenesis.
Project description:The piRNA machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves piRNA-guided cleavage of transposon-derived transcripts. As many piRNAs also appear to have the capacity to target diverse mRNAs, this raises the intriguing possibility that piRNAs may act extensively as siRNAs to degrade specific mRNAs. To directly test this hypothesis, we compared mouse PIWI (MIWI)-associated piRNAs with experimentally identified cleaved mRNA fragments from mouse testes, and observed cleavage sites that predominantly occur at position 10 from the 5' end of putative targeting piRNAs. We also noted strong biases for U and A residues at nucleotide positions 1 and 10, respectively, in both piRNAs and mRNA fragments, features that resemble the pattern of piRNA amplification by the 'ping-pong' cycle. Through mapping of MIWI-RNA interactions by CLIP-seq and gene expression profiling, we found that many potential piRNA-targeted mRNAs directly interact with MIWI and show elevated expression levels in the testes of Miwi catalytic mutant mice. Reporter-based assays further revealed the importance of base pairing between piRNAs and mRNA targets and the requirement for both the slicer activity and piRNA-loading ability of MIWI in piRNA-mediated target repression. Importantly, we demonstrated that proper turnover of certain key piRNA targets is essential for sperm formation. Together, these findings reveal the siRNA-like function of the piRNA machinery in mouse testes and its central requirement for male germ cell development and maturation. CLIP-Seq (Crosslinking Immunoprecipitation coupled with high-throughput sequencing) experiments targeting Miwi in isolated round spermatids from mouse testis.
Project description:Pachytene piRNAs are PIWI-interacting small RNAs abundantly expressed in pachytene spermatocytes and spermatids in adult mouse testes. Both MIWI and MILI-bound pachytene piRNAs have been found enriched in round spermatids. Miwi-null male mice are sterile due to spermiogenic arrest. In C. elegans, sperm-borne piRNAs appear to have an epigenetic role during fertilization and development because progeny of offspring derived from piRNA-deficient sperm display a progressive fertility loss after several generations. In mice, it remains unknown whether MIWI-bound pachytene piRNA-deficient round spermatids can produce offspring, and whether the progeny of offspring derived from MIWI-bound pachytene piRNA-deficient round spermatids also exhibit transgenerational loss of fertility. Here, we report that Miwi KO round spermatids could fertilize both wild type (WT) and Miwi KO oocytes through round spermatid microinjection (ROSI), and produce healthy and fertile offspring despite the aberrant pachytene piRNA profiles in those Miwi KO spermatids. Progeny of ROSI-derived heterozygotes, both male and female, displayed normal fertility for at least three generations when bred with either WT or Miwi KO females. Our data indicate that aberrant MIWI-bound pachytene piRNAs profiles in spermatids do not affect fertilization, early embryonic development, or fertility of the offspring, suggesting a normal pachytene piRNAs profile is not required for paternal transgenerational epigenetic inheritance in mice. Method: Round spermatids were purified from WT and Miwi KO adult testes using a mini-STA-PUT method[Methods Enzymol 1993; 225:84-113.],the purity of round spermatids was >90% based on our previous report[ J Biol Chem 2012; 287:25173-25190.]. Small RNA was isolated from round spermatids using the mirVana RNA isolation kit (Ambion) according to the manufacturer’s instructions. RNA quality and quantity were assessed using the Agilent 2100 Bioanalyzer. Small RNA-Seq was performed on an Ion Proton sequencer (Life Technologies). Libraries were prepared using the Ion Total RNA-Seq Kit v2 (Invitrogen) with biological triplicates for WT and Miwi KO samples. Resutls:Our data indicate that aberrant MIWI-bound pachytene piRNAs profiles in spermatids do not affect fertilization, early embryonic development, or fertility of the offspring, suggesting a normal pachytene piRNAs profile is not required for paternal transgenerational epigenetic inheritance in mice.
Project description:In animal germline cells, Piwi-interacting RNAs (piRNAs) silence retrotransposons through post-transcriptional and transcriptional mechanisms. However, little is known, especially in mammals, about the functions of piRNAs beyond retrotransposon suppression1-5. In mammalian spermatocytes, piRNAs are known to be abundantly expressed6-10. Here, we show that a subset of coding and noncoding RNAs in mouse spermatocytes is degraded by the piRNA pathway. By analyzing the germline trasnscriptome of mice deficient in piRNA biogenesis, we identify hundreds of mRNAs as direct targets of piRNAs. Remarkably, the 3' untranslated region (UTR) of the mRNAs up-regulated in the piRNA pathway mutants are highly enriched with retrotransposon sequenes, implying that these sequences serve as regulatory elements for piRNA-mediated regulation. Furthermore, deficiencies of piRNAs derived from pseudogenes result in increased mRNA levels of their cognate genes, indicating that pseudogenes regulate their functional cognates via piRNAs. Moreover, we identify a large population of testis-enriched long intergenic noncoding RNAs (lincRNAs), some of which are also degraded by the piRNA pathway. Collectively, our results reveal that the piRNA pathway regulates the expression of both mRNAs and lincRNAs in addition to retrotransposon RNAs during meiosis and the key role of retrotransposons and pseudogenes, two major types of genomic sequences, in this regulation by acting as piRNA sources and/or regulatory elements in target RNAs. Late spermatocyte mRNA profiles of Miwi+/- and -/- were analyzed by deep sequencing, in triplicate, using Illumina HiSeq.
Project description:In animal germline cells, Piwi-interacting RNAs (piRNAs) silence retrotransposons through post-transcriptional and transcriptional mechanisms. However, little is known, especially in mammals, about the functions of piRNAs beyond retrotransposon suppression1-5. In mammalian spermatocytes, piRNAs are known to be abundantly expressed6-10. Here, we show that a subset of coding and noncoding RNAs in mouse spermatocytes is degraded by the piRNA pathway. By analyzing the germline trasnscriptome of mice deficient in piRNA biogenesis, we identify hundreds of mRNAs as direct targets of piRNAs. Remarkably, the 3' untranslated region (UTR) of the mRNAs up-regulated in the piRNA pathway mutants are highly enriched with retrotransposon sequenes, implying that these sequences serve as regulatory elements for piRNA-mediated regulation. Furthermore, deficiencies of piRNAs derived from pseudogenes result in increased mRNA levels of their cognate genes, indicating that pseudogenes regulate their functional cognates via piRNAs. Moreover, we identify a large population of testis-enriched long intergenic noncoding RNAs (lincRNAs), some of which are also degraded by the piRNA pathway. Collectively, our results reveal that the piRNA pathway regulates the expression of both mRNAs and lincRNAs in addition to retrotransposon RNAs during meiosis and the key role of retrotransposons and pseudogenes, two major types of genomic sequences, in this regulation by acting as piRNA sources and/or regulatory elements in target RNAs. Early round spermatid mRNA profiles of Miwi+/- and -/- were analyzed by deep sequencing, in triplicate, using Illumina HiSeq.
Project description:The piRNA machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves piRNA-guided cleavage of transposon-derived transcripts. As many piRNAs also appear to have the capacity to target diverse mRNAs, this raises the intriguing possibility that piRNAs may act extensively as siRNAs to degrade specific mRNAs. To directly test this hypothesis, we compared mouse PIWI (MIWI)-associated piRNAs with experimentally identified cleaved mRNA fragments from mouse testes, and observed cleavage sites that predominantly occur at position 10 from the 5' end of putative targeting piRNAs. We also noted strong biases for U and A residues at nucleotide positions 1 and 10, respectively, in both piRNAs and mRNA fragments, features that resemble the pattern of piRNA amplification by the 'ping-pong' cycle. Through mapping of MIWI-RNA interactions by CLIP-seq and gene expression profiling, we found that many potential piRNA-targeted mRNAs directly interact with MIWI and show elevated expression levels in the testes of Miwi catalytic mutant mice. Reporter-based assays further revealed the importance of base pairing between piRNAs and mRNA targets and the requirement for both the slicer activity and piRNA-loading ability of MIWI in piRNA-mediated target repression. Importantly, we demonstrated that proper turnover of certain key piRNA targets is essential for sperm formation. Together, these findings reveal the siRNA-like function of the piRNA machinery in mouse testes and its central requirement for male germ cell development and maturation.