Biology subjects

Iki, T.

Publications and source records attributed to Iki, T..

5 recordsLinked to original sources

bioRxiv2026

PIWI proximity proteome reveals Set1-mediated piRNA biogenesis for transposon silencing in telomere

Silencing complexes formed by PIWI-clade Argonaute (Ago) proteins and PIWI-interacting RNAs (piRNAs) are essential guardians of genome integrity, controlling the deleterious activities of transposable elements (TEs) in animal germline. However, our understanding of PIWI-piRNA-directed TE silencing remains incomplete. Here, we systemically characterize the proximity proteome of PIWI members, Piwi, Aubergine (Aub), and Ago3 in the germline of Drosophila ovaries. Functional screening identifies previously uncharacterized factors involved in TE silencing, including H3K4me3 writer and transcriptional coactivator Set1. Transcriptome analysis reveals that Set1 acts as an indispensable repressor for TEs, particularly those forming telomeres. The involvement of Set1 in Piwi pathway is further supported by its critical role in the production of antisense, TE-targeting piRNAs. Notably, catalytic activity of Set1 is dispensable for TE silencing. Genome-wide chromatin binding analysis using CUT&Tag demonstrates that Set1 preferentially associates with TE sequences and localizes to subtelomeric piRNA cluster loci, suggesting a role in promoting piRNA precursor transcription through direct binding. Collectively, these findings uncover a noncanonical function of Set1 in Piwi-mediated TE silencing and telomere control in germline nuclei.

molecular biology↗

bioRxiv2024

Paralog-dependent Specialization of Paf1C subunit, Ctr9, for Sex Chromosome Gene Regulation and Male Germline Differentiation in Drosophila

Testis-specific gene regulatory mechanisms govern the differentiation of germ cells into mature sperms. However, the molecular underpinnings are not fully elucidated. Here, we show the subunits forming Polymerase Associated Factor 1 Complex (Paf1C), a transcription regulator conserved across eukaryotes, have their individual paralogs predominantly expressed in Drosophila testes. One of these, namely, Ctr9 paralog enriched in testes (Ctr9t) was found to play a critical and nonredundant role in post-meiotic spermatid differentiation and male fertility in D. melanogaster. A proximity proteome analysis provides evidence that Ctr9t forms complexes with other paralog members. We show endogenous Ctr9t is expressed in germ cells at spermatocyte stages, accumulating in a distinct compartment within the nucleolus. There, Ctr9t co-localizes with Spermatocyte arrest (Sa), a testis-specific paralog of TATA-binding protein (TBP)-associated factor 8 (TAF8). We further demonstrate that ctr9t function is crucial for maintaining Sa in the nucleolus, but not vice versa. Transcriptome profiling reveals that Ctr9t acts as an activator for the set of male fertility genes on Y chromosome, but it also acts as a global repressor of X chromosome genes. Collectively, our results shed light on the nucleolus-associated, paralog-dependent regulation of gene expression from sex chromosomes, which ensures the terminal differentiation of male germ cells. Author summaryA wide repertoire of genes takes a coordinated action during sperm formation. However, gene expression during spermatogenesis is controlled by heretofore unelucidated mechanisms. In this study, we show Drosophila expresses testis-specific paralogs of the individual subunits forming a conserved transcription regulator called Paf1C. We generated a loss of function allele of one of the paralog members which we named Ctr9t, and demonstrate that Ctr9t function is crucial for post-meiotic spermatid differentiation and male fertility. Therefore, the paralog has established a nonredundant role for spermatogenesis. Using newly generated antibodies, we show Ctr9t protein is expressed in germ cells at spermatocyte stages and, intriguingly, enriched in the nucleolus. There, Ctr9t interacts with Spermatocyte arrest (Sa), a key transcription factor essential for meiotic and post-meiotic differentiation processes. By further performing whole testis transcriptome analyses, we reveal that Ctr9t acts as a regulator of gene expression from sex chromosomes. Importantly, the activation of male fertility genes located on Y chromosome relies on Ctr9t function, which can explain the defects observed in ctr9t mutant germ cells. Altogether, we propose that Ctr9t acts as a key player in the spermatocyte nucleolus where it controls the expression of sex chromosome genes and ensures functional sperm formation.

genetics↗

bioRxiv2022

Haplotype-resolved de novo genome assemblies of four coniferous tree species

Coniferous trees in gymnosperm are an important source of wood production. Because of their long lifecycle, the breeding programs of coniferous tree are time- and labor-consuming. Genomics could accelerate the selection of superior trees or clones in the breeding programs; however, the genomes of coniferous trees are generally giant in size and exhibit high heterozygosity. Therefore, the generation of long contiguous genome assemblies of coniferous species has been difficult. In this study, we optimized the DNA library preparation protocols and employed high-fidelity (HiFi) long-read sequencing technology to sequence and assemble the genomes of four coniferous tree species, Larix kaempferi, Chamaecyparis obtusa, Cryptomeria japonica, and Cunninghamia lanceolata. Genome assemblies of the four species totaled 13.5 Gb (L. kaempferi), 8.5 Gb (C. obtusa), 9.2 Gb (C. japonica), and 11.7 Gb (C. lanceolata), which covered 99.6% of the estimated genome sizes on average. The contig N50 value, which indicates assembly contiguity, ranged from 1.2 Mb in C. obtusa to 16.0 Mb in L. kaempferi, and the assembled sequences contained, on average, 89.2% of the single-copy orthologs conserved in embryophytes. Assembled sequences representing alternative haplotypes covered 70.3-95.1% of the genomes, suggesting that the four coniferous tree genomes exhibit high heterozygosity levels. The genome sequence information obtained in this study represents a milestone in tree genetics and genomics, and will facilitate gene discovery, allele mining, phylogenetics, and evolutionary studies in coniferous trees, and accelerate forest tree breeding programs.

genomics↗

bioRxiv2022

A pathway to produce non-coding piRNAs from endogenous protein-coding regions supports Drosophila spermatogenesis

PIWI-interacting (pi)RNA pathways control transposable elements (TEs) and endogenous genes in animal gonads, playing important roles in gamete formation. Here, we report a mechanism by which endogenous protein-coding regions, that normally provide their sequences for translation, serve as origins of non-coding piRNA biogenesis in Drosophila melanogaster testes. The products, namely endo-piRNAs, formed silencing complexes with Aubergine (Aub) in germ cells. Proximity proteome combined to functional analyses revealed a testis-specialized chaperone, Cyclophilin 40 (Cyp40), selectively increases endo-piRNA occupancy inside Aub-RISCs aside from other TE-related piRNAs. Moreover, Argonaute 2 (Ago2) activities were found critical for endo-piRNA production. We provide evidence that Ago2-bound short interfering (si)RNAs and micro(mi)RNAs specify precursors and direct endo-piRNA biogenesis. Consistently, Aub and Ago2 cooperate in spermatid differentiation and regulate endogenous genes via endo-piRNA-directed mRNA cleavage. Collectively, our data highlight that Drosophila testes employ a unique strategy to expand the diversity of germline piRNAs supporting late spermatogenesis. HeadlinesO_LIEndogenous protein-coding regions derive non-coding endo-piRNAs C_LIO_LIendo-piRNA and TE-piRNA are produced via distinct mechanisms C_LIO_LIsiRNA and miRNA activities direct secondary piRNA biogenesis C_LIO_LIendo-piRNA pathway controls chromatin and sperm formation C_LI

molecular biology↗

bioRxiv2022

Tejas functions as a core component of nuage assembly and precursor processing in Drosophila piRNA biogenesis

Piwi-interacting RNAs (piRNAs), a class of 23- to 29-nt gonad-specific small RNAs, function to combat transposons in gonads. piRNAs are thought to be processed and amplified in membrane-less granules called nuage in germline cells. In Drosophila, two PIWI family proteins, several Tudor-domain containing (Tdrd) proteins and RNA helicases are assembled at perinuclear region of germline cells, forming nuage to process into piRNAs. Among those, Tejas (Tej), a fly homolog of mouse Tdrd5, has been known as a robust nuage component required for piRNA biogenesis in germline cells, yet its molecular functions remained elusive. To understand its molecular basis on nuage assembly and functions for piRNA biogenesis, we investigated subcellular localization of fluorescent-tagged nuage proteins including Tej and monitored the behavior of piRNA precursors. Tej functions as a core component for assembly of Vasa and Spindle-E to nuage granules through distinct motifs, respectively. The loss of Tej function resulted in malformation of nuage and accumulation of piRNA precursors en route in processing, perturbing further piRNA biogenesis in germline cells. Our study also revealed that the low complexity region of Tej regulates the mobility of nuage by phase separation. Collectively, we propose that Tej plays a pivotal role in processing of piRNA precursors by assembling RNA helicases, Vasa and Spindle-E, to nuage, by controlling the dynamics of nuage components.

cell biology↗