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The Nematode Oscheius tipulae as A Genetic Model for Programmed DNA Elimination [ATAC-seq]

ABSTRACT: Programmed DNA elimination (PDE) is a notable exception to the paradigm of genome integrity. In metazoa, PDE often occurs during early embryogenesis, coincident with germline to somatic cell differentiation. During PDE, portions of genomic DNA are lost, resulting in reduced somatic genomes. Recent studies have described the sequences lost and chromosome behavior in metazoa. However, a system for studying the mechanisms and consequences of PDE in metazoa is lacking. Here, we established a functional and genetic model for PDE in the free-living nematode Oscheius tipulae, a member of the Rhabditidae family, which includes Caenorhabditis elegans. O. tipulae was recently suggested to eliminate DNA. Using staged embryos, we show that O. tipulae PDE occurs during embryogenesis at the 2-16 cell stages, similar to the human/pig parasitic nematode Ascaris. We identified a conserved motif, named Sequence For Elimination (SFE), for all 12 break sites on the six chromosomes at the junction of retained and eliminated DNA. SFE mutants exhibit a “fail-to-eliminate” phenotype only at the modified sites. END-seq revealed that breaks can occur at multiple positions within the SFE, with extensive end resection followed by telomere addition to both retained and eliminated ends. We identified through END-seq in the wild-type embryos, genome sequencing of SFE mutants, and comparative genomics of 23 wild isolates a large number of functional SFEs at the chromosome ends. We suggest these alternative SFEs provide flexibility in the sequences eliminated and a fail-safe mechanism for PDE. These studies establish O. tipulae as a new, attractive model to study the mechanisms and consequences of PDE in a metazoan.

ORGANISM(S): Oscheius tipulae

PROVIDER: GSE213883 | GEO | 2022/09/24

REPOSITORIES: GEO

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The Nematode Oscheius tipulae as A Genetic Model for Programmed DNA Elimination [RNA-seq]

Project description:Programmed DNA elimination (PDE) is a notable exception to the paradigm of genome integrity. In metazoa, PDE often occurs during early embryogenesis, coincident with germline to somatic cell differentiation. During PDE, portions of genomic DNA are lost, resulting in reduced somatic genomes. Recent studies have described the sequences lost and chromosome behavior in metazoa. However, a system for studying the mechanisms and consequences of PDE in metazoa is lacking. Here, we established a functional and genetic model for PDE in the free-living nematode Oscheius tipulae, a member of the Rhabditidae family, which includes Caenorhabditis elegans. O. tipulae was recently suggested to eliminate DNA. Using staged embryos, we show that O. tipulae PDE occurs during embryogenesis at the 2-16 cell stages, similar to the human/pig parasitic nematode Ascaris. We identified a conserved motif, named Sequence For Elimination (SFE), for all 12 break sites on the six chromosomes at the junction of retained and eliminated DNA. SFE mutants exhibit a “fail-to-eliminate” phenotype only at the modified sites. END-seq revealed that breaks can occur at multiple positions within the SFE, with extensive end resection followed by telomere addition to both retained and eliminated ends. We identified through END-seq in the wild-type embryos, genome sequencing of SFE mutants, and comparative genomics of 23 wild isolates a large number of functional SFEs at the chromosome ends. We suggest these alternative SFEs provide flexibility in the sequences eliminated and a fail-safe mechanism for PDE. These studies establish O. tipulae as a new, attractive model to study the mechanisms and consequences of PDE in a metazoan.

2022-09-24 | GSE213885 | GEO

The Nematode Oscheius tipulae as A Genetic Model for Programmed DNA Elimination [END-seq]

2022-09-24 | GSE213884 | GEO

End resection and telomere healing of DNA double-strand breaks during nematode programmed DNA elimination

Project description:Most DNA double-strand breaks (DSBs) are harmful to genome integrity. However, some forms of DSBs are essential to biological processes, such as meiotic recombination and V(D)J recombination. DSBs are also required for programmed DNA elimination (PDE) in ciliates and nematodes. In nematodes, the DSBs are healed with telomere addition. While telomere addition sites have been well-characterized, little is known regarding the DSBs that fragment nematode chromosomes. Here, we used embryos from the nematode Ascaris to study the timing of PDE breaks and examine the DSBs and their end processing. Using END-seq, we characterize the DSB ends and demonstrate that DNA breaks are introduced before mitosis, followed by extensive end resection. The resection profile is unique for each break site, and the resection generates 3’ overhangs before the addition of telomeres. Interestingly, telomere healing occurs much more frequently on retained DSB ends than on eliminated ends. This biased repair of the DSB in Ascaris is likely due to the sequestration of the eliminated DNA into micronuclei, preventing their ends from telomere healing. Additional DNA breaks occur within the eliminated DNA in both Ascaris and Parascaris, ensuring chromosomal breakage and providing a fail-safe mechanism for nematode PDE.

2024-03-15 | GSE260958 | GEO

Comparative Genome Analysis of Programmed DNA Elimination in Nematodes (Parascaris)

Project description:Programmed DNA elimination is a developmentally regulated process leading to the reproducible loss of specific genomic sequences. DNA elimination occurs in unicellular ciliates and a variety of metazoans, including invertebrates and vertebrates. In metazoa, DNA elimination typically occurs in somatic cells during early development, leaving the germline genome intact. Reference genomes for metazoa that undergo DNA elimination are not available. Here, we generated germline and somatic reference genome sequences of the DNA eliminating pig parasitic nematode Ascaris suum and the horse parasite Parascaris univalens. In addition, we carried out in-depth analyses of DNA elimination in the parasitic nematode of humans, Ascaris lumbricoides, and the parasitic nematode of dogs, Toxocara canis. Our analysis of nematode DNA elimination reveals that in all species, repetitive sequences (that differ among the genera) and germline-expressed genes (approximately 1000-2000 or 5%-10% of the genes) are eliminated. Thirty-five percent of these eliminated genes are conserved among these nematodes, defining a core set of eliminated genes that are preferentially expressed during spermatogenesis. Our analysis supports the view that DNA elimination in nematodes silences germline-expressed genes. Over half of the chromosome break sites are conserved between Ascaris and Parascaris, whereas only 10% are conserved in the more divergent T. canis. Analysis of the chromosomal breakage regions suggests a sequence-independent mechanism for DNA breakage followed by telomere healing, with the formation of more accessible chromatin in the break regions prior to DNA elimination. Our genome assemblies and annotations also provide comprehensive resources for analysis of DNA elimination, parasitology research, and comparative nematode genome and epigenome studies.

2017-08-15 | GSE99524 | GEO

Comparative Genome Analysis of Programmed DNA Elimination in Nematodes (Ascaris)

2017-08-15 | GSE99523 | GEO

Chromosome fusion and programmed DNA elimination shape karyotypes of parasitic nematodes [Hi-C]

Project description:A growing list of metazoans undergo programmed DNA elimination (PDE), where a significant amount of DNA is selectively lost from the genome during development. In some nematodes, PDE leads to the removal of the ends of all germline chromosomes. In several species, PDE also eliminates sequences in the interior of the chromosomes, leading to an increased number of somatic chromosomes. The biological significance of these karyotype changes associated with PDE and the origin and evolution of nematode PDE remain largely unknown. Here, we assembled the single pair of germline chromosomes of the horse parasite Parascaris univalens and compared the karyotypes, gene organization within the chromosomes, and PDE features among ascarids. We show that Parascaris converts an XX/XY sex-determination system in the germline into an XX/XO system in the somatic cells. Comparisons of Ascaris, Parascaris, and Baylisascaris chromosomes suggest that PDE existed in the ancestor of these parasites, and their current distinct germline karyotypes were derived from fusion events of the same ancestral smaller chromosomes. PDE resolves these fused germline chromosomes and restores their pre-fusion karyotypes, leading to alterations in genome architecture and gene expression in the somatic cells. Cytological and genomic analyses further reveal the dynamic organization of the Parascaris germline chromosome during meiosis and a potential function for the satellite DNA and the heterochromatin arms. Overall, our results show that chromosome fusion and PDE have been harnessed in these ascarids to shape their karyotypes that could modulate the organization and functions of the genomes.

2024-04-22 | GSE254811 | GEO

Chromosome fusion and programmed DNA elimination shape karyotypes of parasitic nematodes [CUT&RUN]

2024-04-22 | GSE254994 | GEO

Chromosome fusion and programmed DNA elimination shape karyotypes of parasitic nematodes [RNA-seq]

2024-04-22 | GSE254814 | GEO

CENP-A Deposition Defines Sequences for Retention and Elimination during Programmed DNA Elimination in Nematode

Project description:Organisms invest significant effort into maintaining genome stability. However, in diverse groups of eukaryotes, portions or entire chromosomes are lost in early development or during sex determination, a process known as programmed DNA elimination. Little is known about how different segments of the genome are reproducibly retained and discarded during programmed DNA elimination. We tested the hypothesis that selective retention is mediated by regulation of centromere-mediated association of chromosome segments with the mitotic spindle. We report that on the holocentric chromosomes of the nematode Ascaris, the core centromeric histone CENP-A is localized differently in cells undergoing DNA elimination from those undergoing germline mitosis. Prior to DNA elimination, CENP-A is significantly reduced in chromosome regions that will be lost. CENP-A reduction in eliminated genomic regions leads to the absence of kinetochores and microtubule attachment sites necessary for chromosome segregation, and thus the loss of these DNA regions during Ascaris programmed DNA elimination. Our results show that holocentric chromosome organization in Ascaris is regulated and that changes in CENP-A deposition specify which portions of chromosomes will be eliminated during programmed DNA elimination. A total of 62 samples are analyzed. These include: (1). CENP-A ChIP-seq on 12 developmental stages with input and replicates (12 x 2 x 2 samples); (2). CENP-C ChIP-seq on 3 developmental stages with input and replicates (total 8 samples); and (3). Histone marks ChIP-seq with 6 samples

2016-07-15 | E-GEOD-76914 | biostudies-arrayexpress

Tetrahymena thermophila

Project description:Internal eliminated sequences elimination

| PRJNA416874 | ENA