Molecular role of RNA helicases MVH and TDRD9 in PIWI slicing-triggered mammalian piRNA biogenesis and function
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ABSTRACT: PIWI-interacting RNAs (piRNAs) function in the nucleus and cytoplasm of animal germ cells to suppress mobile genetic elements. In the mouse male germline, biogenesis of MIWI2-bound nuclear piRNAs depends on endonuclease activity of cytosolic MILI, but the process is poorly understood. Here we use a mouse model expressing an artificial piRNA precursor to show that MILI slicing of the precursor generates a 16-nt by-product and a pre-piRNA intermediate that requires 3ʹ end processing to mature as a new piRNA. The ability to use the slicer products requires ATPase activity of the RNA helicase MVH, as the catalytic-dead Mvh mutant mice (Mvh-/KI) fail to convert the intermediate into piRNAs, abrogating biogenesis of MIWI2 piRNAs. This results in an early arrest in spermatogenesis and de-repression of transposons. Furthermore, the mutant MVH protein is dominant-negative (Mvh+/KI) as it causes a late-spermatogenic arrest by trapping complexes containing the mysterious pachytene piRNAs and slicer products, uncovering a role for the protein beyond the embryonic germline. In contrast, we find that the ATPase activity of TDRD9 is dispensable for piRNA biogenesis, but is essential for silencing by MIWI2. Our studies implicate distinct RNA helicases in specific steps along the mammalian nuclear piRNA pathway.
Project description:PIWI proteins and their associated small RNAs called PIWI-interacting RNAs (piRNAs) restrict transposon activity in animal gonads to ensure fertility. Distinct biogenesis pathways load piRNAs into the PIWI proteins MILI and MIWI2 in the mouse male embryonic germline. While most of MILI piRNAs derive via a slicer-independent pathway, a MILI slicer endonuclease-initiated pathway loads nuclear MIWI2 with a series of phased piRNAs. Tudor domain-containing 12 (TDRD12) and its interaction partner Exonuclease domain-containing 1 (EXD1) are required for loading MIWI2, but only Tdrd12 is essential for fertility, leaving us with no explanation for the physiological role of Exd1. Using an artificial piRNA precursor, we demonstrate that MILI-triggered piRNA biogenesis is greatly reduced in the Exd1 mutant. The situation deteriorates in the sensitized Exd1 mutant (Exd1-/-; Tdrd12+/-), where diminished MIWI2 piRNA levels de-repress LINE1 retrotransposons, causing infertility. Thus, EXD1 enhances slicing-triggered MIWI2 piRNA biogenesis via a functional interaction with TDRD12.
Project description:Piwi-interacting RNAs are 25-32 nt small RNAs bound to Piwi proteins. To know the steps where factors involved in the piRNA biogenesis (MILI, MIWI2, ZUC (MitoPLD), MVH) work, we sequenced small RNAs from mutant mouse testes and analyzed piRNAs.
Project description:Piwi-interacting RNAs are 25-32 nt small RNAs bound to Piwi proteins. To know the steps where factors involved in the piRNA biogenesis (MILI, MIWI2, ZUC (MitoPLD), MVH) work, we sequenced small RNAs from mutant mouse testes and analyzed piRNAs. Examination of small RNAs in testes of mutant mouse
Project description:The piRNA biogenesis was evaluated in the mouse testes lacking TEX15. Total small RNAs, MILI-, and MIWI2-associated small RNAs from control (Tex15+/-) and Tex15(-/-) knock-out testes were sequenced. Data analysis revealed that the abundance of miRNAs and piRNAs was comparable between control and Tex15 knock-out testes, suggesting that loss of TEX15 function does not impair piRNA biogenesis. However, the relative abundance of MILI- and MIWI2-bound sense piRNAs derived from transposable elements was increased.
Project description:Piwi proteins and piRNAs have conserved functions in transposonM- silencing. The murine Piwi proteins Mili and Miwi2 direct epigeneticM- LINE1 (L1) and intracisternal A particle (IAP) transposon silencingM- during genome reprogramming in the embryonic male germline. PiwiM- proteins are proposed to be piRNA-guided endonucleases that initiateM- secondary piRNA biogenesis . However the actual contribution of theirM- endonuclease activities to piRNA biogenesis and transposon silencingM- remain unknown. To investigate the role of Piwi-catalyzedM- endonucleolytic activity, we engineered point mutations in the mouseM- that substitute the second D to an A in the catalytic triad (DDH) ofM- Mili and Miwi2, generating the MiliDAH and Miwi2DAH alleles,M- M- respectively. Analysis of Mili-bound piRNAs from homozygous MiliDAHM- fetal gonadocytes revealed the failure of transposon piRNA amplification resulting in the stark reduction of piRNA bound withinM- Miwi2 ribonuclear particles (RNPs). We find that Mili-mediated piRNA amplification is selectively required for L1 but not IAP silencing.M- The defective piRNA pathway in MiliDAH mice results in spermatogenic failure and sterility. Surprisingly, homozygous Miwi2DAH mice areM- fertile, transposon silencing is established normally and no defectsM- in secondary piRNA biogenesis are observed. In addition, the hallmarks of piRNA amplification are observed in Miwi2-deficient gonadocytes. WeM- conclude that cycles of intra-Mili secondary piRNA biogenesis fuelM- piRNA amplification that is selectively required for L1 silencing.M-
Project description:In mice, the PIWI-piRNA pathway is essential to re-establish transposon silencing during male germline reprogramming. The cytoplasmic PIWI protein MILI mediates piRNA-guided transposon RNA cleavage as well as piRNA amplification. MIWI2-bound piRNAs and its nuclear localization are proposed to be dependent upon MILI function. Here, we demonstrate the existence of a piRNA biogenesis pathway that in the absence of MILI that sustains partial MIWI2 function and reprogramming activity.
Project description:PIWI-interacting RNAs (piRNAs) guide PIWI proteins to suppress transposable elements in animal gonads. Here we demonstrate that in the mouse embryonic male germline, endonucleolytic cleavage (slicing) of a transcript by cytosolic MILI acts as a trigger to initiate its further 5??3? processing into non-overlapping fragments. These fragments accumulate as new piRNAs within the nuclear PIWI protein MIWI2. We identify Exonuclease domain-containing 1 (EXD1) as a partner of the established MIWI2 piRNA biogenesis factor TDRD12. Although EXD1 homodimers are inactive as a nuclease, it functions as an RNA adapter within a PET (PIWI-EXD1-Tdrd12) complex. Loss of Exd1 impacts biogenesis of MIWI2 piRNAs and displays a reduction in sequences generated by MILI slicing. This results in selective depletion of repeat piRNAs that target active retrotransposons like LINE1, which are de-repressed in the mutant. We propose that PIWI slicing and EXD1 promote coordination of nucleo-cytoplasmic silencing via piRNA biogenesis. Immunoprecipitated or total small RNAs were purified and sequenced from P0 mouse testis of Exd1+/- and Exd1 -/- mice. Testes of three males were pooled together and MILI and MIWI2 immunoprecipitation was performed or total small RNAs were purified. Two replicas from different pools were prepared. For Rosa26-pi reporter mouse P0 testes of three males were pooled together and MILI and MIWI2 immunoprecipitation was performed.
Project description:PIWI-interacting RNAs (piRNAs) guide PIWI proteins to suppress transposable elements in animal gonads. Here we demonstrate that in the mouse embryonic male germline, endonucleolytic cleavage (slicing) of a transcript by cytosolic MILI acts as a trigger to initiate its further 5??3? processing into non-overlapping fragments. These fragments accumulate as new piRNAs within the nuclear PIWI protein MIWI2. We identify Exonuclease domain-containing 1 (EXD1) as a partner of the established MIWI2 piRNA biogenesis factor TDRD12. Although EXD1 homodimers are inactive as a nuclease, it functions as an RNA adapter within a PET (PIWI-EXD1-Tdrd12) complex. Loss of Exd1 impacts biogenesis of MIWI2 piRNAs and displays a reduction in sequences generated by MILI slicing. This results in selective depletion of repeat piRNAs that target active retrotransposons like LINE1, which are de-repressed in the mutant. We propose that PIWI slicing and EXD1 promote coordination of nucleo-cytoplasmic silencing via piRNA biogenesis.
Project description:In diverse organisms, the highly-conserved Piwi proteins bind to a complex class of small non-coding RNAs called piRNAs, and are essential for germline stem cell maintenance, transposon silencing, fertility, and offspring viability1. By homology with other Argonautes, Piwi proteins have been proposed and later reported to possess endonuclease activity in vitro, effected by its conserved aspartate catalytic triad2,3. Indeed, mutation of these residues in one of the three mouse PIWI proteins, MILI, affects the production of Line 1 piRNAs and spermatogenesis4. In Drosophila, the conserved slicer function has been proposed to be crucial for all Piwi proteins in piRNA amplification and transposon silencing5. Here, we report in vivo evidence that, in contrast to common belief, the catalytic triad of Piwi is not required for the function of PIwi in the germline for stem cell maintenance, fertility, transposon silencing, or piRNA biogenesis. In addition, it is not required for piRNA biogenesis in the soma where Piwi is the sole Piwi-subfamily protein involved in the process. These observations, together with the recent findings on MILI and MIWI2 triad mutant, indicate that even though the slicer function may be required for a subset of piRNA-mediated process, it is overall inconsequential for the function of Piwi proteins Assess the role of the endonuclease activity of Piwi in all known biological processes that involve Piwi function in Drosophila ovary
Project description:In diverse organisms, the highly-conserved Piwi proteins bind to a complex class of small non-coding RNAs called piRNAs, and are essential for germline stem cell maintenance, transposon silencing, fertility, and offspring viability1. By homology with other Argonautes, Piwi proteins have been proposed and later reported to possess endonuclease activity in vitro, effected by its conserved aspartate catalytic triad2,3. Indeed, mutation of these residues in one of the three mouse PIWI proteins, MILI, affects the production of Line 1 piRNAs and spermatogenesis4. In Drosophila, the conserved slicer function has been proposed to be crucial for all Piwi proteins in piRNA amplification and transposon silencing5. Here, we report in vivo evidence that, in contrast to common belief, the catalytic triad of Piwi is not required for the function of PIwi in the germline for stem cell maintenance, fertility, transposon silencing, or piRNA biogenesis. In addition, it is not required for piRNA biogenesis in the soma where Piwi is the sole Piwi-subfamily protein involved in the process. These observations, together with the recent findings on MILI and MIWI2 triad mutant, indicate that even though the slicer function may be required for a subset of piRNA-mediated process, it is overall inconsequential for the function of Piwi proteins