Reduced pachytene piRNAs and translation underlie spermiogenic arrest in Maelstrom mutant mice.
ABSTRACT: Pachytene piRNAs are a class of Piwi-interacting small RNAs abundant in spermatids of the adult mouse testis. They are processed from piRNA primary transcripts by a poorly understood mechanism and, unlike fetal transposon-derived piRNAs, lack complementary targets in the spermatid transcriptome. We report that immunopurified complexes of a conserved piRNA pathway protein Maelstrom (MAEL) are enriched in MIWI (Piwi partner of pachytene piRNAs), Tudor-domain proteins and processing intermediates of pachytene piRNA primary transcripts. We provide evidence of functional significance of these complexes in Mael129 knockout mice that exhibit spermiogenic arrest with acrosome and flagellum malformation. Mael129-null mutant testes possess low levels of piRNAs derived from MAEL-associated piRNA precursors and exhibit reduced translation of numerous spermiogenic mRNAs including those encoding acrosome and flagellum proteins. These translation defects in haploid round spermatids are likely indirect, as neither MAEL nor piRNA precursors associate with polyribosomes, and they may arise from an imbalance between pachytene piRNAs 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 RNAs (piRNAs) engage PIWI proteins to silence transposons and promote germ cell development in animals. In diverse species, piRNA biogenesis occurs near the mitochondrial surface, and involves mitochondrial membrane-anchored factors. In mice, two cytoplasmic PIWI proteins, MIWI and MILI, receive processed pachytene piRNAs at intermitochodrial cement (IMC). However, how MIWI and MILI are initially recruited to the IMC to engage multiple steps of piRNA processing is unclear. Here, we show that mitochondria-anchored TDRKH controls multiple steps of pachytene piRNA biogenesis in mice. TDRKH specifically recruits MIWI, but not MILI, to engage the piRNA pathway. It is required for the production of the entire MIWI-bound piRNA population and enables trimming of MILI-bound piRNAs. The failure to recruit MIWI to the IMC with TDRKH deficiency results in loss of MIWI in the chromatoid body, leading to spermiogenic arrest and piRNA-independent retrotransposon LINE1 de-repression in round spermatids. Our findings identify a mitochondrial surface-based scaffolding mechanism separating the entry and actions of two critical PIWI proteins in the same piRNA pathway to drive piRNA biogenesis and germ cell development.
Project description:Pachytene piRNAs are MIWI-/MILI-bound small RNAs abundantly expressed in pachytene spermatocytes and round spermatids in adult mouse testes. Miwi knockout (KO) male mice are sterile due to spermiogenic arrest. In Caenorhabditis elegans, sperm-borne piRNAs appear to have an epigenetic role during fertilization and development because progeny of individuals with piRNA-deficient gametes display a progressive loss of fertility after several generations. In mice, it remains unknown whether pachytene piRNA-deficient round spermatids can produce offspring, and whether the progeny of Miwi mutants also exhibits transgenerational, progressive fertility loss. Here, we report that Miwi KO round spermatids could fertilize both wild-type (WT) and Miwi KO oocytes through round spermatid injection, and could produce healthy and fertile offspring despite the global downregulation of both MIWI-/MILI-bound pachytene piRNAs. 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-/MILI-bound pachytene piRNA profiles in spermatids do not affect fertilization, early embryonic development, or fertility of the offspring, suggesting that pachytene piRNAs might not be required for paternal transgenerational epigenetic inheritance in mice.
Project description:Germ cells implement elaborate mechanisms to protect their genetic material and to regulate gene expression during differentiation. Piwi proteins bind Piwi-interacting RNAs (piRNAs), small germline RNAs whose biogenesis and functions are still largely elusive. We used high-throughput sequencing after cross-linking and immunoprecipitation (HITS-CLIP) coupled with RNA-sequencing (RNA-seq) to characterize the genome-wide target RNA repertoire of Mili (Piwil2) and Miwi (Piwil1), two Piwi proteins expressed in mouse postnatal testis. We report the in vivo pathway of primary piRNA biogenesis and implicate distinct nucleolytic activities that process Piwi-bound precursor transcripts. Our studies indicate that pachytene piRNAs are the end products of RNA processing. HITS-CLIP demonstrated that Miwi binds spermiogenic mRNAs directly, without using piRNAs as guides, and independent biochemical analyses of testis mRNA ribonucleoproteins (mRNPs) established that Miwi functions in the formation of mRNP complexes that stabilize mRNAs essential for spermiogenesis.
Project description:Spermatogenesis in mammals is characterized by two waves of piRNA expression: one corresponds to classic piRNAs responsible for silencing retrotransponsons and the second wave is predominantly derived from nontransposon intergenic regions in pachytene spermatocytes, but the function of these pachytene piRNAs is largely unknown. Here, we report the involvement of pachytene piRNAs in instructing massive mRNA elimination in mouse elongating spermatids (ES). We demonstrate that a piRNA-induced silencing complex (pi-RISC) containing murine PIWI (MIWI) and deadenylase CAF1 is selectively assembled in ES, which is responsible for inducing mRNA deadenylation and decay via a mechanism that resembles the action of miRNAs in somatic cells. Such a highly orchestrated program appears to take full advantage of the enormous repertoire of diversified targeting capacity of pachytene piRNAs derived from nontransposon intergenic regions. These findings suggest that pachytene piRNAs are responsible for inactivating vast cellular programs in preparation for sperm production from ES.
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. Overall design: In Miwi KO males, round spermatid production in the seminiferous tubules proceed up to step 4 (J Anat. 2000 Feb; 196(Pt 2): 217–232. ), which provides us with an opportunity to use steps 1-4 round spermatids to fertilize eggs through round spermatid microinjection (ROSI). In this study, we aimed to answer the following questions: 1) Is the pachytene piRNA profile altered in Miwi-deficient round spermatids? 2) Are the Miwi-deficient round spermatids competent for fertilization? 3) If so, are the progeny derived from ROSI offspring using Miwi-deficient round spermatids fertile? 4) Does paternal MIWI inactivation in mice phenocopy CSR-1 inactivation in C. elegans and display the “gremlin mortal” epigenetic inheritance? Here, we report that MIWI deficiency leads to altered pachytene piRNAs profiles and Miwi-deficient round spermatids can fertilize the eggs and produce normal offspring. Unlike C. elegans, the absence of paternal MIWI did not induce epigenetic “germline-mortal” phenotype in mice.
Project description:PIWI-interacting RNAs (piRNAs) are small noncoding RNAs that bind PIWI family proteins exclusively expressed in the germ cells of mammalian gonads. MIWI2-associated piRNAs are essential for silencing transposons during primordial germ cell development, and MIWI-bound piRNAs are required for normal spermatogenesis during adulthood in mice. Although piRNAs have long been regarded as germ cell-specific, increasing lines of evidence suggest that somatic cells also express piRNA-like RNAs (pilRNAs). Here, we report the detection of abundant pilRNAs in somatic cells, which are similar to MIWI-associated piRNAs mainly expressed in pachytene spermatocytes and round spermatids in the testis. Based on small RNA deep sequencing and quantitative PCR analyses, pilRNA expression is dynamic and displays tissue specificity. Although pilRNAs are similar to pachytene piRNAs in both size and genomic origins, they have a distinct ping-pong signature. Furthermore, pilRNA biogenesis appears to utilize a yet to be identified pathway, which is different from all currently known small RNA biogenetic pathways. In addition, pilRNAs appear to preferentially target the 3'-UTRs of mRNAs in a partially complementary manner. Our data suggest that pilRNAs, as an integral component of the small RNA transcriptome in somatic cell lineages, represent a distinct population of small RNAs that may have functions similar to germ cell piRNAs.
Project description:Animal germ cells produce PIWI-interacting RNAs (piRNAs), small silencing RNAs that suppress transposons and enable gamete maturation. Mammalian transposon-silencing piRNAs accumulate early in spermatogenesis, whereas pachytene piRNAs are produced later during postnatal spermatogenesis and account for >95% of all piRNAs in the adult mouse testis. Mutants defective for pachytene piRNA pathway proteins fail to produce mature sperm, but neither the piRNA precursor transcripts nor the trigger for pachytene piRNA production is known. Here, we show that the transcription factor A-MYB initiates pachytene piRNA production. A-MYB drives transcription of both pachytene piRNA precursor RNAs and the mRNAs for core piRNA biogenesis factors including MIWI, the protein through which pachytene piRNAs function. A-MYB regulation of piRNA pathway proteins and piRNA genes creates a coherent feedforward loop that ensures the robust accumulation of pachytene piRNAs. This regulatory circuit, which can be detected in rooster testes, likely predates the divergence of birds and mammals.
Project description:PIWI-interacting RNAs (piRNAs) play an important role in gametogenesis, fertility and embryonic development. The current study investigated the effect of different doses of pregnant mare serum gonadotrophin/human chorionic gonadotrophin (PMSG/hCG) and repeated ovarian stimulation (OS) on the expression of the Mili, Miwi, Mael, Tdrd1, Tdrd9, qnd Mitopld genes, which have crucial roles in the biogenesis and function of piRNAs. Here, we found that after treatment with 7.5 I.U. PMSG/hCG and two repeated rounds of OS, both the mRNA and protein levels of Tdrd9, Tdrd1 and Mael showed the greatest decrease in the ovarian tissue, but the plasma E2 levels showed the strongest increases (p<0.05). However, we found that the Mitopld, Miwi and Mili gene levels were decreased significantly after treatment with 12.5 I.U. PMSG/hCG. Our results suggested that exogenous gonadotropin administration leads to a significant decrease in the expression of the Mili, Miwi, Mael, Tdrd1, Tdrd9 and Mitopld genes, which are critically important in the piRNA pathway, and the changes in the expression levels of Tdrd9, Tdrd1 and Mael may be associated with plasma E2 levels. New comprehensive studies are needed to reduce the potential effects of OS on the piRNA pathway, which silences transposable elements and maintains genome integrity, and to contribute to the safety of OS.
Project description:Repression of retrotransposons is essential for genome integrity during germ cell development and is tightly controlled through epigenetic mechanisms. In primordial germ cells, protein arginine N-methyltransferase (Prmt5) is involved in retrotransposon repression by methylating Piwi proteins, which is part of the piRNA pathway. Here, we show that in mice, genetic inactivation of coprs (which is highly expressed in testis and encodes a histone-binding protein required for the targeting of Prmt5 activity) affects the maturation of spermatogonia to spermatids. Mass spectrometry analysis revealed the presence of Miwi in testis protein lysates immunoprecipitated with an anti-Coprs antibody. The observed deregulation of Miwi and pachytene pre-piRNAs levels and the derepression of LINE1 repetitive sequences observed in coprs-/- mice suggest that Coprs is implicated in genome surveillance mechanisms.