Escalation of genome defense capacity enables control of an expanding meiotic driver.

From RNA interference to chromatin silencing, diverse genome defense pathways silence selfish genetic elements to safeguard genome integrity. Despite their diversity, different defense pathways share a modular organization, where numerous specificity factors identify diverse targets and common effectors silence them. In the PIWI-interacting RNA (piRNA) pathway, target RNAs are first identified by complementary base pairing with piRNAs and then silenced by PIWI-clade nucleases.

Escalation of genome defense capacity enables control of an expanding meiotic driver.

From RNA interference to chromatin silencing, diverse genome defense pathways silence selfish genetic elements to safeguard genome integrity. Despite their diversity, different defense pathways share a modular organization, where numerous specificity factors identify diverse targets and common effectors silence them. In the PIWI-interacting RNA (piRNA) pathway, which controls selfish elements in the metazoan germline, diverse target RNAs are first identified by complementary base pairing with piRNAs and then silenced by PIWI-clade nucleases via enzymatic cleavage.

SUMOylation of Bonus, the homolog of Transcription Intermediary Factor 1, safeguards germline identity by recruiting repressive chromatin complexes to silence tissue-specific genes.

The conserved family of Transcription Intermediary Factors (TIF1) proteins consists of key transcriptional regulators that control transcription of target genes by modulating chromatin state. Unlike mammals that have four TIF1 members, only encodes one member of the family, Bonus. Bonus has been implicated in embryonic development and organogenesis and shown to regulate several signaling pathways, however, its targets and mechanism of action remained poorly understood.

Impact of Germline Depletion of Bonus on Chromatin State in Ovaries.

Gene expression is controlled via complex regulatory mechanisms involving transcription factors, chromatin modifications, and chromatin regulatory factors. Histone modifications, such as H3K27me3, H3K9ac, and H3K27ac, play an important role in controlling chromatin accessibility and transcriptional output. In vertebrates, the Transcriptional Intermediary Factor 1 (TIF1) family of proteins play essential roles in transcription, cell differentiation, DNA repair, and mitosis.

Maternally inherited siRNAs initiate piRNA cluster formation.

PIWI-interacting RNAs (piRNAs) guide transposable element repression in animal germ lines. In Drosophila, piRNAs are produced from heterochromatic loci, called piRNA clusters, which act as information repositories about genome invaders. piRNA generation by dual-strand clusters depends on the chromatin-bound Rhino-Deadlock-Cutoff (RDC) complex, which is deposited on clusters guided by piRNAs, forming a positive feedback loop in which piRNAs promote their own biogenesis.

SUMOylation of Bonus, the homolog of Transcription Intermediary Factor 1, safeguards germline identity by recruiting repressive chromatin complexes to silence tissue-specific genes.

The conserved family of Transcription Intermediary Factors (TIF1) proteins consists of key transcriptional regulators that control transcription of target genes by modulating chromatin state. Unlike mammals that have four TIF1 members, only encodes one member of the family, Bonus. Bonus has been implicated in embryonic development and organogenesis and shown to regulate several signaling pathways, however, its targets and mechanism of action remained poorly understood.

Pervasive SUMOylation of heterochromatin and piRNA pathway proteins.

Genome regulation involves complex protein interactions that are often mediated through post-translational modifications (PTMs). SUMOylation-modification by the small ubiquitin-like modifier (SUMO)-has been implicated in numerous essential processes in eukaryotes. In , SUMO is required for viability and fertility, with its depletion from ovaries leading to heterochromatin loss and ectopic transposon and gene activation.

Bacterial Argonaute Proteins Aid Cell Division in the Presence of Topoisomerase Inhibitors in Escherichia coli.

Prokaryotic Argonaute (pAgo) proteins are guide-dependent nucleases that function in host defense against invaders. Recently, it was shown that TtAgo from Thermus thermophilus also participates in the completion of DNA replication by decatenating chromosomal DNA. Here, we show that two pAgos from cyanobacteria Synechococcus elongatus (SeAgo) and Limnothrix rosea (LrAgo) are active in heterologous Escherichia coli and aid cell division in the presence of the gyrase inhibitor ciprofloxacin, depending on the host double-strand break repair machinery.

Bacterial Argonaute nucleases reveal different modes of DNA targeting in vitro and in vivo.

Prokaryotic Argonaute proteins (pAgos) are homologs of eukaryotic Argonautes (eAgos) and are also thought to play a role in cell defense against invaders. However, pAgos are much more diverse than eAgos and little is known about their functional activities and target specificities in vivo. Here, we describe five pAgos from mesophilic bacteria that act as programmable DNA endonucleases and analyze their ability to target chromosomal and invader DNA.

Genetic control of a sex-specific piRNA program.

Sexually dimorphic traits in morphologies are widely studied, but those in essential molecular pathways remain largely unexplored. Previous work showed substantial sex differences in Drosophila gonadal piRNAs, which guide PIWI proteins to silence selfish genetic elements, thereby safeguarding fertility. However, the genetic control mechanisms of piRNA sexual dimorphism remain unknown.

Specific targeting of plasmids with Argonaute enables genome editing.

Prokaryotic Argonautes (pAgos) are programmable nucleases involved in cell defense against invading DNA. In vitro, pAgos can bind small single-stranded guide DNAs to recognize and cleave complementary DNA. In vivo, pAgos preferentially target plasmids, phages and multicopy genetic elements.

Programmable RNA targeting by bacterial Argonaute nucleases with unconventional guide binding and cleavage specificity.

Argonaute proteins are programmable nucleases that have defense and regulatory functions in both eukaryotes and prokaryotes. All known prokaryotic Argonautes (pAgos) characterized so far act on DNA targets. Here, we describe a new class of pAgos that uniquely use DNA guides to process RNA targets.

Transposon-taming piRNAs in the germline: Where do they come from?

Mutations in the piRNA pathway protein components lead to transposon activation and fertility defects. In contrast, Gebert et al., (2021) saw no defects in transposon silencing or fertility when they deleted three large germline piRNA clusters in D.

RDC complex executes a dynamic piRNA program during Drosophila spermatogenesis to safeguard male fertility.

piRNAs are small non-coding RNAs that guide the silencing of transposons and other targets in animal gonads. In Drosophila female germline, many piRNA source loci dubbed "piRNA clusters" lack hallmarks of active genes and exploit an alternative path for transcription, which relies on the Rhino-Deadlock-Cutoff (RDC) complex. RDC was thought to be absent in testis, so it remains to date unknown how piRNA cluster transcription is regulated in the male germline.

Binding of guide piRNA triggers methylation of the unstructured N-terminal region of Aub leading to assembly of the piRNA amplification complex.

PIWI proteins use guide piRNAs to repress selfish genomic elements, protecting the genomic integrity of gametes and ensuring the fertility of animal species. Efficient transposon repression depends on amplification of piRNA guides in the ping-pong cycle, which in Drosophila entails tight cooperation between two PIWI proteins, Aub and Ago3. Here we show that post-translational modification, symmetric dimethylarginine (sDMA), of Aub is essential for piRNA biogenesis, transposon silencing and fertility.

piRNA-mediated gene regulation and adaptation to sex-specific transposon expression in male germline.

Small noncoding piRNAs act as sequence-specific guides to repress complementary targets in Metazoa. Prior studies in ovaries have demonstrated the function of the piRNA pathway in transposon silencing and therefore genome defense. However, the ability of the piRNA program to respond to different transposon landscapes and the role of piRNAs in regulating host gene expression remain poorly understood.

Genes and the piRNA Pathway in Speciation and Reproductive Isolation of .

One of the main conditions of the species splitting from a common precursor lineage is the prevention of a gene flow between diverging populations. The study of interspecific hybrids allows to reconstruct the speciation mechanisms and to identify hybrid incompatibility factors that maintain post-zygotic reproductive isolation between closely related species. The regulation, evolution, and maintenance of the testis-specific genetic system in is the subject of investigation worldwide.

Recognition of double-stranded DNA by the Rhodobacter sphaeroides Argonaute protein.

In contrast to eukaryotic Argonaute proteins that act on RNA targets, prokaryotic Argonautes (pAgos) can target DNA, using either small RNA or small DNA guides for its recognition. Since pAgos can recognize only a single strand of DNA and lack a helicase activity, it remains unknown how double-stranded DNA can be bound both in vitro and in vivo. Here, using in vitro reconstitution and footprinting assays we analyze formation of specific complexes with target DNA by a catalytically inactive pAgo, RsAgo from Rhodobacter sphaeroides programmed with small guide RNAs.

Repression of interrupted and intact rDNA by the SUMO pathway in .

Ribosomal RNAs (rRNAs) are essential components of the ribosome and are among the most abundant macromolecules in the cell. To ensure high rRNA level, eukaryotic genomes contain dozens to hundreds of rDNA genes, however, only a fraction of the rRNA genes seems to be active, while others are transcriptionally silent. We found that individual rDNA genes have high level of cell-to-cell heterogeneity in their expression in .

DNA targeting and interference by a bacterial Argonaute nuclease.

Members of the conserved Argonaute protein family use small RNA guides to locate their mRNA targets and regulate gene expression and suppress mobile genetic elements in eukaryotes. Argonautes are also present in many bacterial and archaeal species. Unlike eukaryotic proteins, several prokaryotic Argonaute proteins use small DNA guides to cleave DNA, a process known as DNA interference.

Genome-wide DNA sampling by Ago nuclease from the cyanobacterium .

Members of the conserved Argonaute (Ago) protein family provide defence against invading nucleic acids in eukaryotes in the process of RNA interference. Many prokaryotes also contain Ago proteins that are predicted to be active nucleases; however, their functional activities in host cells remain poorly understood. Here, we characterize the and properties of the SeAgo protein from the mesophilic cyanobacterium .