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Results for “neocentromere”

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PubMed2026

Neocentromeres fail to maintain DNA methylation boundaries, driving CENP-A drift, instability, and chromosome missegregation.

Centromere identity is specified by CENP-A, a histone H3 variant that epigenetically defines centromere position. How CENP-A is maintained at one location in rapidly evolving centromeric DNA is unknown. Using single-cell-derived clones of human cell lines, we demonstrate heterogeneity in CENP-A position within cell populations at neocentromeres and a native centromere. CENP-A heterogeneity is accompanied by heterogeneous DNA methylation patterns, with DNA methylation shifting according to CENP-A position. We demonstrate centromere epigenetic plasticity over extended proliferation, with native centromeres maintaining stable DNA methylation boundaries, but neocentromeres exhibiting DNA methylation instability, boundary loss, and increased missegregation. Finally, we show that neocentromeres are more sensitive to DNA methylation inhibition than native centromeres, and that this inhibition is accompanied by expanded CENP-A-enriched domains and increased missegregation. This study supports a role for DNA methylation boundaries in maintaining centromere position, stability, and function and highlights the intrinsic instability of DNA methylation at neocentromeres.

CENP-A↗

PubMed2025

Haplotype-resolved telomere-to-telomere genome assembly of Populus lasiocarpa unveils retrotransposon-driven centromere evolution.

Centromeres, essential for chromosome segregation, exhibit remarkable evolutionary dynamism in sequence composition and structural organization. Here, we report the first haplotype-resolved, telomere-to-telomere genome assembly of Populus lasiocarpa (PLAS) and precisely map all 38 functional centromeres through CENH3 ChIP-Seq. Unlike classical satellite-rich centromeres in model plants, PLAS centromeres lack abundant satellite arrays but are dominated by retrotransposons, particularly RLG and RIL elements, which form intricate nested TE arrays within the functional centromeric regions, disrupting their structural integrity and driving their evolution. Comparative analysis with P. trichocarpa reveals a conserved retrotransposon-dominated architecture, despite minimal sequence conservation. We propose a cyclic model of centromere evolution in which autonomous retrotransposons destabilize functional centromeres through epigenetic erosion, triggering neocentromere formation at pericentromeric sites enriched in transposable elements (TEs) and tandem repeats (TRs). These neocentromeres either succumb to recurrent retrotransposon invasions or stabilize through KARMA-mediated TR expansion, ultimately giving rise to satellite-rich centromeres. Our work redefines centromeres as dynamic, epigenetically plastic domains shaped by retrotransposon-TR antagonism, challenging the satellite-centric paradigm and offering novel insights into plant genome evolution.

Retroelements↗

PubMed2025

The genomic origin of the unique chaetognath body plan.

The emergence of animal phyla, each with their unique body plan, was a rapid event in the history of animal life, yet its genomic underpinnings are still poorly understood1. Here we investigate at the genomic, regulatory and cellular levels, the origin of one of the most distinctive animal phyla, the chaetognaths, whose organismal characteristics have historically complicated their phylogenetic placement2,3. We show that these characteristics are reflected at the cell-type level by the expression of genes that originated in the chaetognath lineage, contributing to adaptation to planktonic life at the sensory and structural levels4. Similarly to other members of gnathiferans (which also include rotifers and several other microscopic phyla)5,6, chaetognaths have undergone accelerated genomic evolution with gene loss and chromosomal fusions7,8. Furthermore, they secondarily duplicated thousands of genes9,10, without evidence for a whole-genome duplication, yielding, for instance, tandemly expanded Hox genes, as well as many phylum-specific genes. We also detected repeat-rich highly methylated neocentromeres and a simplified DNA methylation toolkit that is involved in mobile element repression rather than transcriptional control. Consistent with fossil evidence11,12, our observations suggest that chaetognaths emerged after a phase of morphological simplification through a reinvention of organ systems paralleled by massive genomic reorganization, explaining the uniqueness of their body plan.

Animals↗

PubMed2025

Two CENH3 paralogs in the green alga Chlamydomonas reinhardtii have a redundantly essential function and associate with ZeppL-LINE1 elements.

Centromeres in eukaryotes are defined by the presence of histone H3 variant CENP-A/CENH3. Chlamydomonas encodes two predicted CENH3 paralogs, CENH3.1 and CENH3.2, that have not been previously characterized. We generated peptide antibodies to unique N-terminal epitopes for each of the two predicted Chlamydomonas CENH3 paralogs as well as an antibody against a shared CENH3 epitope. All three CENH3 antibodies recognized proteins of the expected size on immunoblots and had punctate nuclear immunofluorescence staining patterns. These results are consistent with both paralogs being expressed and localized to centromeres. CRISPR-Cas9-mediated insertional mutagenesis was used to generate predicted null mutations in either CENH3.1 or CENH3.2. Single mutants were viable but cenh3.1 cenh3.2 double mutants were not recovered, confirming that the function of CENH3 is essential. We sequenced and assembled two chromosome-scale Chlamydomonas genomes from strains CC-400 and UL-1690 (a derivative of CC-1690) with complete centromere sequences for 17/17 and 14/17 chromosomes respectively, enabling us to compare centromere evolution across four isolates with near complete assemblies. These data revealed significant changes across isolates between homologous centromeres including mobility and degeneration of ZeppL-LINE1 (ZeppL) transposons that comprise the major centromere repeat sequence in Chlamydomonas. We used cleavage under targets and tagmentation (CUT&Tag) to purify and map CENH3-bound genomic sequences and found enrichment of CENH3-binding almost exclusively at predicted centromere regions. An interesting exception was chromosome 2 in UL-1690, which had enrichment at its genetically mapped centromere repeat region as well as a second, distal location, centered around a single recently acquired ZeppL insertion. The CENH3-bound regions of the 17 Chlamydomonas centromeres ranged from 63.5 kb (average lower estimate) to 175 kb (average upper estimate). The relatively small size of its centromeres suggests that Chlamydomonas may be a useful organism for testing and deploying artificial chromosome technologies.

Chlamydomonas reinhardtii↗