Biology subjects

Cecchini, K.

Publications and source records attributed to Cecchini, K..

6 recordsLinked to original sources

bioRxiv2024

Mouse Pachytene piRNAs Cleave Hundreds of Transcripts,But Alter the Steady-State Abundance of Only a Minority of Targets

In animals, 18-35-nt piRNAs guide PIWI proteins to regulate complementary RNAs. During male meiosis, mammals produce an exceptionally abundant class of piRNAs called pachytene piRNAs. Pachytene piRNAs are required for spermatogenesis and have been proposed to control gene expression by various mechanisms. Here, we show that pachytene piRNAs regulate targets predominantly, if not exclusively, by endonucleolytic cleavage. Remarkably, pachytene piRNAs slice hundreds of RNAs, yet a change in steady-state level is detectable for a small fraction of transcripts. Our data suggest that cleavage of the few targets whose abundance is reduced significantly by piRNAs is essential for male fertility. Other pachytene piRNA targets are enriched for highly transcribed genes, which may explain why piRNA cleavage is often inconsequential for the steady-state abundance of targets. We propose that the retention of pachytene piRNAs throughout mammalian evolution is driven by the selective advantage conferred by a tiny minority of piRNAs.

molecular biology↗

bioRxiv2022

Relaxed targeting rules allow PIWI-clade Argonaute proteins to silence ever-mutating transposons

In animals, piRNAs direct PIWI-clade Argonaute proteins to slice complementary transposon transcripts. Transposons can evade silencing through target site mutations. We report that PIWIs efficiently cleave transcripts only partially paired to their piRNA guide. Measurements of mouse PIWI protein affinity and cleavage rates for thousands of RNAs in vitro and in vivo show that PIWI slicing tolerates mismatches to any target nucleotide, including those flanking the scissile phosphate. Although piRNA 5 terminal nucleotides accelerate target finding, they are dispensable for binding or catalysis--unlike AGO-clade Argonautes, which require uninterrupted siRNA:target pairing from the seed to the nucleotides past the scissile bond. PIWIs are thus better equipped than AGOs to target newly acquired or rapidly diverging endogenous transposons without recourse to novel small RNA guides.

molecular biology↗

bioRxiv2021

The testis-specific transcription factor TCFL5 responds to A MYBto elaborate the male meiotic program in placental mammals

In male mice, the transcription factor (TF) A-MYB initiates reprogramming of gene expression after spermatogonia enter meiosis. We report that A-MYB activates Tcfl5, a testis-specific TF first produced in pachytene spermatocytes. Subsequently, A-MYB and TCFL5 reciprocally reinforce their own transcription to establish an extensive circuit that regulates meiosis. TCFL5 promotes transcription of genes required for mRNA turnover, pachytene piRNA production, meiotic exit, and spermiogenesis. This transcriptional architecture is conserved in rhesus macaque, suggesting TCFL5 plays a central role in meiosis and spermiogenesis in placental mammals. Tcfl5em1/em1 mutants are sterile, and spermatogenesis arrests at the mid- or late-pachytene stage of meiosis.

genetics↗

bioRxiv2020

Terminal Modification, Sequence, and Length Determine Small RNA Stability in Animals

In animals, piRNAs, siRNAs, and miRNAs silence transposons, fight viral infections, and regulate gene expression. piRNA biogenesis concludes with 3' terminal trimming and 2'-O-methylation. Both trimming and methylation influence piRNA stability. Here, we report that trimming and methylation protect mouse piRNAs from different decay mechanisms. In the absence of 2'-O-methylation, mouse piRNAs with extensive complementarity to long RNAs become unstable. In flies, 2'-O-methylation similarly protects both piRNAs and siRNAs from complementarity-dependent destabilization. Animal miRNAs are unmethylated, and complementarity-dependent destabilization helps explain differences in miRNA decay rates in both mice and flies. In contrast, trimming protects mouse piRNAs from a separate degradation pathway unaffected by target complementarity but sensitive to the 3' terminal, untrimmed sequence. Because distinct sets of mouse piRNAs are protected by each of these mechanisms, loss of both trimming and 2'-O-methylation causes the piRNA pathway to collapse, demonstrating that these two small RNA modifications collaborate to stabilize piRNAs. HighlightsO_LI2'-O-methylation protects mouse and fly piRNAs from complementarity-dependent decay C_LIO_LI2'-O-methylation protects fly siRNAs with extensive complementarity to long RNAs C_LIO_LIComplementarity to long RNAs predicts the half-life of fly and mouse miRNAs C_LIO_LIMouse pre-piRNA decay reflects both pre-piRNA sequence and PIWI protein identity C_LI

molecular biology↗

bioRxiv2018

An Evolutionarily Conserved piRNA-producing Locus Required for Male Mouse Fertility

Pachytene piRNAs, which comprise >80% of small RNAs in the adult mouse testis, have been proposed to bind and regulate target RNAs like miRNAs, cleave targets like siRNAs, or lack biological function altogether. Although piRNA pathway protein mutants are male sterile, no biological function has been identified for any mammalian piRNA-producing locus. Here, we report that males lacking piRNAs from a conserved mouse pachytene piRNA locus on chromosome 6 (pi6) produce sperm with defects in capacitation and egg fertilization. Moreover, heterozygous embryos sired by pi6-/- fathers show reduced viability in utero. Molecular analyses suggest that pi6 piRNAs repress gene expression by cleaving mRNAs encoding proteins required for sperm function. pi6 also participates in a network of piRNA-piRNA precursor interactions that initiate piRNA production from a second piRNA locus on chromosome 10 as well as pi6 itself. Our data establish a direct role for pachytene piRNAs in spermiogenesis and embryo viability.\n\nHighlightsO_LINormal male mouse fertility and spermiogenesis require piRNAs from the pi6 locus\nC_LIO_LISperm capacitation and binding to the zona pellucida of the egg require pi6 piRNAs\nC_LIO_LIHeterozygous embryos sired by pi6-/- fathers show reduced viability in utero\nC_LIO_LIDefects in pi6 mutant sperm reflect changes in the abundance of specific mRNAs.\nC_LI

genetics↗

bioRxiv2018

PIWI Proteins Act at Multiple Steps in the Production of Their Own Guides

In animals, piRNAs guide PIWI-proteins to silence transposons and regulate gene expression. The mechanisms for making piRNAs have been proposed to differ among cell types, tissues, and animals. Our data instead suggest a single model that explains piRNA production in most animals. piRNAs initiate piRNA production by guiding PIWI proteins to slice precursor transcripts. Next, PIWI proteins direct the stepwise fragmentation of the sliced precursor transcripts, yielding tail-to-head strings of phased pre-piRNAs. Our analyses detect evidence for this piRNA biogenesis strategy across an evolutionarily broad range of animals including humans. Thus, PIWI proteins initiate and sustain piRNA biogenesis by the same mechanism in species whose last common ancestor predates the branching of most animal lineages. The unified model places PIWI-clade Argonautes at the center of piRNA biology and suggests that the ancestral animal--the Urmetazoan--used PIWI proteins both to generate piRNA guides and to execute piRNA function.

molecular biology↗