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Author(s): Amy A. Caudy [1, 3]; René F. Ketting [2, 3]; Scott M. Hammond [1, 4]; Ahmet M. Denli [1]; Anja M. P. Bathoorn [1, 2]; Bastiaan B. J. Tops [...]

Research has been conducted on the double-stranded RNAs suppressing homologous gene expression via RNA interference or post-transcriptional silencing. The characterization of Caenorhabditis elegans ortholog of Dicer has been carried out in vivo and in vitro and the results indicate that Dicer is involved in the maturation of the small RNA molecule regulating developmental silencing.

A model in which MUT-7, guided by transposon-derived dsRNA, represses transposition by degrading transposon-specific messengers and prevents thereby transposase production and transposition, is proposed. It appears that NRAi may work by dsRNA-directed enzymatic RNA degradation. One Tc1 silenced strain of C. elegans has been has been mutagenized. Mutants in which Tc1 was activated in the germline were isolated.

Author(s): René F. Ketting [1]; Ronald H. A. Plasterk (corresponding author) [1] Originally discovered in plants [1, 2], the phenomenon of co-suppression by transgenic DNA has since been observed in [...]

Author(s): Ahmet M. Denli [1]; Bastiaan B. J. Tops [2]; Ronald H. A. Plasterk [2]; René F. Ketting [2]; Gregory J. Hannon (corresponding author) [1] Mature microRNAs (miRNAs) are generated [...]

The crystal structure of the complex between the N-terminal DNA-binding domain of Tc3 transposase and an oligomer of transposon DNA has been determined. The specific DNA-binding domain contains three -helices, of which two form a helix­turn­helix (HTH) motif. The recognition of transposon DNA by the transposase is mediated through base-specific contacts and complementarity between protein and sequence-dependent deformations of the DNA. The HTH motif makes four base-specific contacts with the major groove, and the N-terminus makes three base-specific contacts with the minor groove. The DNA oligomer adopts a non-linear B-DNA conformation, made possible by a stretch of seven G:C base pairs at one end and a TATA sequence towards the other end. Extensive contacts (seven salt bridges and 16 hydrogen bonds) of the protein with the DNA backbone allow the protein to probe and recognize the sequence-dependent DNA deformation. The DNA-binding domain forms a dimer in the crystals. Each monomer binds a separate transposon end, implying that the dimer plays a role in synapsis, necessary for the simultaneous cleavage of both transposon termini. [ABSTRACT FROM AUTHOR]

Ribosome biogenesis is vital for sustaining stem cell properties, yet its regulatory mechanisms are obscure. Herein, we show unique properties of zebrafish meioc mutants in which spermatogonial stem cells (SSCs) do not differentiate or upregulate rRNAs. Meioc colocalized with Piwil1 in perinuclear germ granules, but Meioc depletion resulted in Piwil1 accumulation in nucleoli. Nucleolar Piwil1 interacted with 45S pre-rRNA. piwil1 +/- spermatogonia with reduced Piwil1 upregulated rRNAs, and piwil1 +/- ;meioc -/- spermatogonia recovered differentiation later than those in meioc -/- . Further, Piwil1 interacted with Setdb1 and HP1α, and meioc -/- spermatogonia exhibited high levels of H3K9me3 and methylated CpG in the 45S-rDNA region. These results indicate that zebrafish SSCs silence rRNA transcription with repressive marks similar to Drosophila piRNA targets of RNA polymerase II, and that Meioc has a unique function on preventing localization of Piwil1 in nucleoli to upregulate rRNA transcripts and to promote SSC differentiation., Competing Interests: Competing interest statement: The authors declare no competing financial interests.

Primary microRNA (pri-miRNA) transcripts are processed by the Microprocessor, a protein complex that includes the ribonuclease Drosha and its RNA binding partner DGCR8/Pasha. We developed a live, whole animal, fluorescence-based sensor that reliably monitors pri-miRNA processing with high sensitivity in C. elegans . Through a forward genetic selection for alleles that desilence the sensor, we identified a mutation in the conserved G residue adjacent to the namesake W residue of Pasha's WW domain. Using genome editing we also mutated the W residue and reveal that both the G and W residue are required for dimerization of Pasha and proper assembly of the Microprocessor. Surprisingly, we find that the WW domain also facilitates nuclear localization of Pasha, which in turn promotes nuclear import or retention of Drosha. Furthermore, depletion of Pasha or Drosha causes both components of the Microprocessor to mislocalize to the cytoplasm. Thus, Pasha and Drosha mutually regulate each other's spatial expression in C. elegans ., Competing Interests: COMPETING INTERESTS The authors declare no competing interests.