Project description:The PIWI/piRNA pathway serves as a conserved RNA-directed immune mechanism that suppresses transposons and promotes fertility. The biogenesis of piRNAs has been extensively investigated since their discovery, yet the mechanisms governing piRNA degradation remain poorly understood. This study determines the half-lives of thousands of C. elegans piRNAs, revealing a broad range from less than 1 hour to over 20 hours. Notably, piRNAs with 3' terminal uridines are degraded faster than those with 3' guanines or cytosines, suggesting that 3' uridines induce nucleolytic degradation. We identify DISL-2, a 3' to 5' exoribonuclease, as a key enzyme responsible for degrading piRNAs with templated 3' uridines as well as non-templated 3' uridines added by Poly(U) polymerase PUP-1. Furthermore, DISL-2 acts as a quality control factor to target piRNAs that are improperly processed at their 3' ends. Together, our findings advance the understanding of piRNA homeostasis by determining piRNA half-lives and identifying factors involved piRNA decay.
Project description:The PIWI/piRNA pathway acts as a conserved RNA-directed immune mechanism that suppresses transposons and promotes fertility. The biogenesis of piRNAs has been extensively investigated since their discovery, yet the mechanisms governing piRNA degradation remain poorly understood. Here, we systematically measure the half-lives of thousands of C. elegans piRNAs, revealing a broad range from less than 1 hour to over 20 hours. Notably, piRNAs with 3' terminal uridines (U) degrade faster than those with 3' guanines or cytosines, suggesting that 3' uridines induce nucleolytic degradation. We identify DISL-2, a 3' to 5' exoribonuclease, as a key enzyme responsible for degrading piRNAs with templated 3' uridines as well as non-templated 3' uridines added by Poly(U) polymerase PUP-1. Furthermore, DISL-2 acts as a quality control factor to target piRNAs that are improperly processed at their 3' ends. Together, these findings advance our understanding of piRNA homeostasis by determining piRNA half-lives and identifying factors involved piRNA decay.
Project description:Identification of defects in piRNAs and piRNA precursors Sequencing of small RNAs (18-30nt). Sample treatments: Secondary siRNAs in C. elegans carry a 5' triphosphate and this has to be removed prior to cloning, hence the use of 5' polyphosphatase treatment to reveal this population. TAP (tobacco acid pyrophosphatase) is another enzyme that removes 5' triphosphate but it also removes 5' CAP structures- we used this to look for piRNA precursor sequences in C. elegans that have a 5' cap.
Project description:In animal germ lines, The Piwi/piRNA pathway plays a crucial role in safeguarding genome integrity and promoting fertility. Following transcription from discrete genomic loci, piRNA precursors undergo nucleolytic processing at both 5’ and 3’ ends. The ribonuclease PARN-1 and its orthologs mediate piRNA 3' trimming in worms, insects and mammals. Yet, the significance of this evolutionarily conserved processing step is not well understood. Employing C. elegans as a model organism, our recent work has demonstrated that 3' trimming protects piRNAs against non-templated nucleotide additions and degradation. In this study, we present an unexpected finding that C. elegans deficient for PARN-1 accumulate a heretofore uncharacterized RNA species termed anti-piRNAs, which are antisense to piRNAs. These anti-piRNAs associate with Piwi proteins and display the propensity for a length of 17-19 nucleotides and 5’ guanine and adenine residues. We show that untrimmed pre-piRNAs in parn-1 mutants are modified by the terminal nucleotidyl transferase RDE-3 and erroneously targeted by the RNA dependent RNA polymerase EGO-1, thereby giving rise to anti-piRNAs. Taken together, our work identifies a previously unknown class of small RNAs upon loss of parn-1 and provides mechanistic insight to activities of RDE-3, EGO-1 and Piwi proteins.
Project description:Argonaute proteins are essential players in RNA silencing pathways, and their N-terminal extensions, particularly in the PIWI clade, often harbor conserved sequences like RG motifs. Despite their prevalence in Argonaute proteins, the role of these motifs remains poorly understood. In this study, we focus on the RG motifs within the N-terminal region of Caenorhabditis elegans PRG-1, a PIWI clade Argonaute. Using sequence alignment across Caenorhabditis species, we identify three conserved RG motifs that are methylated, as confirmed by mass spectrometry. The region surrounding these motifs is intrinsically disordered, as predicted by disorder algorithms and structural modeling. While the RG motifs are critical for fertility, germline morphology, and piRNA silencing, they are not required for PRG-1 expression, localization, or piRNA loading. Notably, mutation of the RG motifs results in defects in downstream small RNA production, specifically the depletion of mutator class siRNAs, without affecting piRNA biogenesis. These findings suggest that the RG motifs of PRG-1 play a crucial role in linking piRNA-mediated silencing to siRNA production, and that their function is critical for fertility and germline maintenance in C. elegans. Despite these defects, the phenotypic severity in the RG mutant is milder than in a PRG-1 null mutant, highlighting the complexity of PRG-1 function and its post-translational modifications.
Project description:Remarkably, tens of thousands of piwi-interacting RNAs (piRNAs) arise from a minimal number of discrete clustered regions in many organisms. However, it remains unclear if organization into these domains contributes to the highly coordinated, germline-specific expression of these small RNAs. Here, we show that SNPC-4, the DNA-binding subunit of the small nuclear RNA activating protein complex (SNAPc), binds piRNA clusters in a germline-specific manner and is required for global piRNA expression in C. elegans. Within piRNA domains, SNPC-4 not only binds at discrete sites through its established sequence motif, but also exhibits widely distributed binding across the region. Intriguingly, discrete peaks are not found at every piRNA, but instead occur frequently at Pol III-occupied tRNA genes, which have been previously implicated in chromatin organization. Given its unique binding pattern, we suggest that SNPC-4 promotes robust piRNA expression by establishing a permissive chromatin environment at clusters specifically in the germ line.
Project description:PIWI-interacting RNAs (piRNAs) are genomically-encoded small RNAs that regulate germ cell development and guarantee germline integrity. Mature piRNAs engage Piwi Argonaute proteins to silence complementary transcripts, including transposable elements and endogenous genes. To date, piRNA biogenesis mechanisms are still unclear. Here, we show that the RNA Polymerase II subunit RPB-9 is required to promote transcription elongation at piRNA loci. Through genetic and biochemical experiments, we demonstrate that rpb-9-mediated piRNA production is needed to repress two DNA transposon families and a subset of somatic genes in the C. elegans germline.
Project description:Autophagy is a catabolic membrane trafficking process involved in degradation of cellular constituents through lysosomes, which maintains cell and tissue homeostasis. While much attention has been focused on autophagic turnover of cytoplasmic materials, little is known regarding the role of autophagy in degrading nuclear components. Here we report that autophagy machinery mediates degradation of nuclear lamina in mammalian cells, a process we term laminophagy. The autophagy protein LC3 is present in the nucleus and directly interacts with the nuclear lamina protein Lamin B1, and associates with lamin-associated domains (LADs) on chromatin. This interaction does not downregulate Lamin B1 during starvation, but mediates nuclear lamina degradation upon tumorigenic insults, such as by oncogenic Ras. Laminophagy is achieved by nucleus-to-cytosol transport that delivers Lamin B1 to lysosome for degradation. Inhibiting autophagy or LC3-Lamin B1 interaction prevents oncogenic Ras-induced Lamin B1 loss and delays oncogene-induced cell cycle arrest. Our study unveils a role of autophagy in degrading nuclear materials, and suggests laminophagy as a guarding mechanism protecting cells from tumorigenesis.
Project description:PIWI-interacting RNAs (piRNAs) are genomically-encoded small RNAs that regulate germ cell development and guarantee germline integrity. Mature piRNAs engage Piwi Argonaute proteins to silence complementary transcripts, including transposable elements and endogenous genes. To date, piRNA biogenesis mechanisms are still unclear. Here, we show that the RNA Polymerase II subunit RPB-9 is required to promote transcription elongation at piRNA loci. Through genetic and biochemical experiments, we demonstrate that rpb-9-mediated piRNA production is needed to repress two DNA transposon families and a subset of somatic genes in the C. elegans germline.
Project description:Piwi-interacting RNAs (piRNAs) play essential roles in silencing repetitive elements to promote fertility in metazoans. Nearly one-third of the ~15,000 piRNA loci in the C. elegans hermaphrodite are enriched during spermatogenesis, whereas >2,000 piRNAs are enriched during oogenesis. However, the mechanism underlying this sex-specific regulation is unknown. Here we identify SNPC-1.3, a variant of a conserved subunit of the snRNA activating protein complex, as a male-specific piRNA transcription factor. Binding of SNPC-1.3 at male piRNA loci drives spermatogenic piRNA transcription and requires the core piRNA transcription factor SNPC-4. Loss of snpc-1.3 leads to depletion of spermatogenic piRNAs and defects in male-dependent fertility. Furthermore, TRA-1, a master regulator of sex determination, binds to the snpc-1.3 promoter and represses its expression during oogenesis. Loss of TRA-1 targeting causes ectopic expression of snpc-1.3 and male piRNAs during oogenesis. Thus, sexual dimorphic regulation of snpc-1.3 coordinates male and female piRNA expression during germline development.