Characterization and parental contribution of piRNAs and endo-siRNAs to mouse zygotes.
ABSTRACT: Transposable elements (TEs) are widely represented in eukaryotic genomes. Recently, a set of small RNAs known as rasRNAs (repeat-associated small RNAs) have been related to the down-regulation of TEs conferring a means to safeguard genome integrity. Two key members of the rasRNAs group are piRNAs and endo-siRNAs. In this study, we have performed a comparative analysis of piRNAs and endo-siRNAs present in mouse oocytes, spermatozoa and zygotes, identified by deep sequencing and bioinformatic analysis. Both piRNAs and endo-siRNAs regulate TEs in addition to other repetitive elements such as tRNAs and rRNAs, suggesting an alternative role of rasRNAs with regard to translation regulation. The detection of piRNAs and endo-siRNAs in sperm cells and revealed also in zygotes, hints to their potential delivery to oocytes during fertilization. However, a comparative assessment of the three cell types indicates that both piRNAs and endo-siRNAs are mainly maternally inherited. Finally, we have assessed the role of the different rasRNA molecules in connection with amplification processes by way of the “ping-pong cycle”. Our results suggest that the ping-pong cycle can act on other rasRNAs, such as tRNA- and rRNA-derived fragments, thus not only being restricted to TEs during gametogenesis, as was evidenced in spermatozoa, oocytes and zygotes. Comparative analysis from deep sequencing of piRNAs and endo-siRNAs in mouse oocytes, spermatozoa and zygotes
Project description:The small non-coding RNAs (sncRNAs) are considered as postranscriptional key regulators of male germ cell development. In addition to microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs), other sncRNAs generated from small nucleolar RNAs (snoRNAs), tRNAs or rRNAs processing may also play important regulatory roles in spermatogenesis. By next generation sequencing (NGS), we characterized the different sncRNA populations detected at three milestone stages in male germ differentiation: primordial germ cells (PGCs) at 13.5 dpc, pubertal spermatogonia cells, and mature spermatozoa. In order to assess the potential transmission of the sncRNAs through the mature spermatozoa during fertilization, the sncRNA population detected in male germ cells was also compared with sncRNAs detected in unfertilized mouse oocytes and zygotes. Combining the data obtained by NGS and microarrays from whole PGC and spermatogonia transcriptome, we defined the potential regulatory roles of specific miRNAs and their validated targets. Similar to miRNAs, both the small RNAs derived from snoRNAs and the piRNAs, could be involved in the postranscriptional regulation of mRNA transcripts during the male germ development. Finally, our results strongly suggest that the small RNAs-derived from tRNAs and rRNAs are interacting with PIWI proteins, and specifically with MILI. These new classes of piRNAs are not generated by the ping-pong pathway and could be the source of primary piRNAs. Comparative analysis from deep sequencing of piRNAs and endo-siRNAs in mouse oocytes, spermatozoa and zygotes
Project description:nbr/CG9247 gene regulates the length of a subset of miRNAs. It is not clear whether Nbr affects the length of other classes of small RNAs, such as piRNAs and endo-siRNAs. To address this, we compared small RNA population in wild-type, Df(2L)BSC312/+, nbr null (nbrf02257/Df(2L)BSC312), (nbr null; pCaSper-nbr (WT)), and (nbr null; pCaSper-nbr (D435A,E437A)). This approach revealed that, in addition to miRNAs, piRNAs and endo-siRNAs were also affected in their length in nbr null and nbr null; pCaSper-nbr (D435A,E437A). 4-7d ovaries were dissected in PBS, and 40ug total RNA was prepared from wild-type, Df(2L)BSC312/+, nbr null (nbrf02257/Df(2L)BSC312), (nbr null; pCaSper-nbr (WT)), and (nbr null; pCaSper-nbr (D435A,E437A)), using Trizol Reagent (#15596-018, Life Technologies, Carlsbad, CA) following the manufacturer's protocol. The small RNAs between ~16 to ~29 nt in size were purified from 15% TBE-urea gel (#EC6885BOX, Life Technologies, Carlsbad, CA). Small RNA libraries were prepared using Illumina's TruSeq small RNA sample preparation kit (#RS-200-0012, Illumina, Inc. San Diego, CA), following the manufacturer's protocol The libraries were sequenced on HiSeq2000 platform (Illumina).
Project description:Transposable elements (TEs), whose propagation can result in severe damage to the host genome, are silenced in the animal gonad by Piwi-interacting RNAs (piRNAs). piRNAs produced in the ovaries are deposited in the embryonic germline and initiate TE repression in the germline progeny. Whether the maternally transmitted piRNAs play a role in the silencing of somatic TEs is, however, unknown. Here we show that maternally transmitted piRNAs from the tirant retrotransposon in Drosophila are required for the somatic silencing of the TE and correlate with an increase in histone H3K9 trimethylation an active tirant copy. Comparison of tirant piRNAs in two Drosophila simulans natural populations.
Project description:The maintenance of genome integrity is an essential trait to the successful transmission of genetic information. In animal germ cells, piRNAs guide PIWI proteins to silence transposable elements (TEs) in order to maintain genome integrity. In insects, most of TE silencing in the germline is achieved by secondary piRNAs that are produced by a feed-forward loop (the ping-pong cycle), which requires the piRNA-directed cleavages of two types of RNAs: mRNAs of functional euchromatic TEs and heterochromatic transcripts that contain defective TE sequences. The first cleavage which initiates such amplification loop remains poorly understood. Taking advantage of the existence of strains that are devoid of functional copies of the LINE-like I-element, we report that in such Drosophila ovaries, the initiation of a ping-pong cycle is achieved only by secondary I-element piRNAs that are produced in the ovary and deposited in the embryonic germline. This unusual secondary piRNA biogenesis, detected in the absence of functional I-element copies, results from the processing of sense and antisense transcripts of several different defective I-elements. Once acquired, for instance after ancestor aging, this capacity to produce heterochromatic-only secondary piRNAs is partially transmitted through generations via maternal piRNAs. Furthermore, such piRNAs acting as ping-pong initiators in a chromatin-independent manner confer to the progeny a high capacity to repress the I-element mobility. Our study explains at the molecular level the basis for epigenetic memory of maternal immunity that protects females from hybrid dysgenesis caused by transposition of paternally inherited functional I-elements. Comparison of Drosophila small RNA populations in ovaries and/or eggs from 3-day-old or 25-day-old females.
Project description:Although piwi-interacting RNAs (piRNAs) play pivotal roles in spermatogenesis, little is known about piRNAs in the seminal plasma of infertile males. In this study, we systematically investigated the profiles of seminal plasma piRNAs in infertile males to identify piRNAs that are altered during infertility and evaluate their diagnostic value. Seminal plasma samples were obtained from 211 infertile patients (asthenozoospermia and azoospermia) and 91 fertile controls. High-throughput sequencing technology was employed to screen piRNA profiles in seminal plasma samples pooled from healthy controls and infertile patients. The results identified 61 markedly altered piRNAs in the infertile patient groups compared with the control group. Next, a quantitative RT-PCR assay was conducted in the training and validation sets to measure and confirm the concentrations of altered piRNAs. The results identified a panel of 5 piRNAs that were significantly decreased in the seminal plasma of infertile patients compared with healthy controls. The areas under the ROC curves for these piRNAs ranged from 0.796 to 0.996, suggesting that the diagnostic potential of these 5 piRNAs to distinguish asthenozoospermic and azoospermic individuals from healthy controls was high. In summary, this study identifies a panel of piRNAs that can accurately distinguish fertile from infertile males. This finding may provide pathophysiological clues that are involved in the development of infertility. Fresh samples were collected and stored at -80℃.Total RNA of seminal plasma were extracted and solexa sequencing was performed.
Project description:Colonization of genomes by a new selfish genetic element is detrimental to the host species and must lead to an efficient, repressive response. In vertebrates as well as in Drosophila, piRNAs repress transposons in the germ line while endogenous siRNAs take on this role in somatic cells. For endo-siRNAs as well as for piRNAs, it is unclear how an efficient response can be initiated de novo. Our experiments establish that the endo-siRNA pathway will target artificially introduced sequences without the need for a pre-existing template in the genome. This response is also triggered in transiently transfected cells, thus genomic integration is not essential. Deep sequencing revealed that corresponding endo-siRNAs are generated throughout the sequence, but preferentially from transcribed regions. Examination of 3 different cell lines.
Project description:Eukaryotic cells express several classes of small RNAs that regulate gene expression and ensure genome maintenance. Endogenous siRNAs (endo-siRNAs) and Piwi-interacting RNAs (piRNAs) mainly control gene and transposon expression in the germline, while microRNAs (miRNAs) generally function in post-transcriptional gene silencing in both somatic and germline cells. To provide an evolutionary and developmental perspective on small RNA pathways in nematodes, we identified and characterized known and novel small RNA classes through gametogenesis and embryo development in the parasitic nematode Ascaris suum and compared them with known small RNAs of Caenorhabditis elegans. piRNAs, Piwi-clade Argonautes, and other proteins associated with the piRNA pathway have been lost in Ascaris. miRNAs are synthesized immediately following fertilization in utero, prior to pronuclear fusion, and before the first cleavage of the zygote. This is the earliest expression of small RNAs ever described at a developmental stage long thought to be transcriptionally quiescent. A comparison of the two classes of Ascaris endo-siRNAs, 22G-RNAs and 26G-RNAs, to those in C. elegans, suggests great diversification and plasticity in the use of small RNA pathways during spermatogenesis in different nematodes. Our data reveal conserved characteristics of nematode small RNAs as well as features unique to Ascaris that illustrate significant flexibility in the use of small RNAs pathways, some of which are likely an adaptation to Ascaris’ life cycle and parasitism. We generated transcriptomes from Ascaris germline and embryos for de-novo assembly as well as cDNA expression profiles. Two types of libraries were prepared: 1) sheared, full-length cDNA synthesized using a combination of oligo-dT and random hexamer priming and 2) cDNA prepared from RNA first chemically sheared and then double-stranded cDNA prepared using ramom hexamer priming.
Project description:Transposable elements are a serious threat for genome integrity and their control via small RNA mediated silencing pathways is an ancient strategy. The fruit fly Drosophila melanogaster has two silencing mechanisms that repress TEs expression: endogenous siRNAs (esiRNAs or endo-siRNAs) and Piwi-interacting small RNAs (piRNAs). The biogenesis of endo-siRNAs involves Loqs-PD, which acts predominantly during processing of dsRNA by Dcr-2, and R2D2 that primarily helps to direct siRNAs for loading into Ago2. We provide deep sequencing evidence consistent with the idea that R2D2 and Loqs-PD can function in part redundantly. Certain transposons display a preference for either dsRBD-protein for production or loading; this appeared to correlate neither with overall abundance, classification of the transposon or a specific site of genomic origin. The endo-siRNA biogenesis pathway in the germline operates according to the same principles as the existing model for the soma, and its impairment does not significantly affect piRNAs. Expanding the analysis, we confirmed the occurrence of somatic piRNA-like RNAs (pilRNAs) that show a ping-pong signature. We detected expression of the Piwi-family protein mRNAs only barely above background, indicating that the somatic pilRNAs may arise from a small sub-population of somatic cells that express a functional piRNA pathway. small RNA sampling experiment; small RNAs were prepared from head & thorax as well as dissected ovaries of Adult female Drosophila melanogaster. We used homozygous mutants of the dsRBD proteins Loqs and r2d2 to determine their contribution to the biogenesis of transposon-derived small RNAs. Heterozygous mutant animals served as control. For each RNA sample, we performed one deep-sequencing run without any treatment, and in parallel one sequencing run after periodate oxidation and beta-elimination. After this treatment, only Ago2, Piwi, Aub and Ago3-loaded small RNAs remain as they carry a 2'-O-methyl modification at their 3'-end. This helps to determine the loading status of the small RNAs detected. In total 8 different RNA samples were prepared and 16 libraries were sequenced.
Project description:In Drosophila, siRNAs are classified as endo- or exo-siRNAs based on their origin. Both are processed from double-stranded RNA precursors by Dcr-2, then loaded into the Argonaute protein Ago2. While exo-siRNAs serve to defend the cell against viruses, endo-siRNAs restrict the spread of selfish DNA in somatic cells, analogous to piRNAs in the germ line. Endo- and exo-siRNAs display a differential requirement for double-stranded RNA binding domain proteins (dsRBPs): R2D2 is needed to load exo-siRNAs into Ago2 while the PD isoform of Loquacious (Loqs-PD) stimulates Dcr-2 during the nucleolytic processing of hairpin-derived endo-siRNAs. In cell culture assays, R2D2 antagonizes Loqs-PD in endo-siRNA silencing and Loqs-PD is an inhibitor of RNA interference. Loqs-PD can interact via the C-terminus unique to this isoform with the DExH/D-helicase domain of Drosophila Dcr-2, where binding of R2D2 has also been localized. Separation of the two pathways is not complete; rather, the dicing and Ago2-loading steps appear uncoupled, analogous to the corresponding steps in miRNA biogenesis. Analysis of deep sequencing data further demonstrates that in r2d2 mutant flies, siRNAs can be loaded into Ago2 but not all siRNA classes are equally proficient for this. Thus, the canonical Ago2-RISC loading complex can be bypassed under certain circumstances. Examination of small RNAs from two different mutant strains as well as the corresponding heterozygous controls