Project description:Programmed DNA elimination (PDE) is a notable exception to genome integrity, characterized by significant DNA loss during development. In many nematodes, PDE is initiated by DNA double-strand breaks (DSBs), which lead to chromosome fragmentation and subsequent DNA loss. However, the mechanism of nematode programmed DNA breakage remains largely unclear. Interestingly, in the human and pig parasitic nematode Ascaris, no conserved motif or sequence structures are present at chromosomal breakage regions (CBRs), suggesting the recognition of CBRs may be sequence-independent. Using Hi-C, we revealed that Ascaris CBRs engage in three-dimensional (3D) interactions before PDE, indicating that physical contacts between break regions may contribute to the PDE process. The 3D interactions are established in both Ascaris male and female germlines, demonstrating inherent genome organization associated with the CBRs and to-be-eliminated sequences. In contrast, in the unichromosomal horse parasite Parascaris univalens, transient pairwise interactions between neighboring CBRs that will form the ends of future somatic chromosomes were observed only during PDE. Intriguingly, we found that Ascaris PDE, which converts 24 germline chromosomes into 36 somatic ones, induces specific compartmentalization changes. Remarkably, Parascaris PDE generates the same set of 36 somatic chromosomes, and the 3D compartment changes following PDE are consistent between the two species. Overall, our findings suggest that CBRs spatially demarcate the retained and eliminated DNA and may contribute to their spatial organization during Ascaris PDE. We also demonstrated that the 3D genome reorganization of the somatic chromosomes in these nematodes following PDE is evolutionary and developmentally conserved.

2026-01-10 | GSE315650 | GEO

Parascaris equorum

Project description:Parascaris equorum overview

| PRJNA421573 | ENA

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

Project description:Parascaris univalens ivermectin response

| PRJNA680223 | ENA