Limits...
Cellular and Molecular Features of Developmentally Programmed Genome Rearrangement in a Vertebrate (Sea Lamprey: Petromyzon marinus).

Timoshevskiy VA, Herdy JR, Keinath MC, Smith JJ - PLoS Genet. (2016)

Bottom Line: Programmed genome rearrangements (PGRs) result in the reproducible loss of ~20% of the genome from somatic cell lineages during early embryogenesis.Here we identify epigenetic silencing events that are associated with the programmed elimination of DNA and describe the spatiotemporal dynamics of PGR during lamprey embryogenesis.During early embryogenesis a majority of micronuclei (~60%) show strong enrichment for repressive chromatin modifications (H3K9me3 and 5meC).

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Kentucky, Lexington, Kentucky, United States of America.

ABSTRACT
The sea lamprey (Petromyzon marinus) represents one of the few vertebrate species known to undergo large-scale programmatic elimination of genomic DNA over the course of its normal development. Programmed genome rearrangements (PGRs) result in the reproducible loss of ~20% of the genome from somatic cell lineages during early embryogenesis. Studies of PGR hold the potential to provide novel insights related to the maintenance of genome stability during the cell cycle and coordination between mechanisms responsible for the accurate distribution of chromosomes into daughter cells, yet little is known regarding the mechanistic basis or cellular context of PGR in this or any other vertebrate lineage. Here we identify epigenetic silencing events that are associated with the programmed elimination of DNA and describe the spatiotemporal dynamics of PGR during lamprey embryogenesis. In situ analyses reveal that the earliest DNA methylation (and to some extent H3K9 trimethylation) events are limited to specific extranuclear structures (micronuclei) containing eliminated DNA. During early embryogenesis a majority of micronuclei (~60%) show strong enrichment for repressive chromatin modifications (H3K9me3 and 5meC). These analyses also led to the discovery that eliminated DNA is packaged into chromatin that does not migrate with somatically retained chromosomes during anaphase, a condition that is superficially similar to lagging chromosomes observed in some cancer subtypes. Closer examination of "lagging" chromatin revealed distributions of repetitive elements, cytoskeletal contacts and chromatin contacts that provide new insights into the cellular mechanisms underlying the programmed loss of these segments. Our analyses provide additional perspective on the cellular and molecular context of PGR, identify new structures associated with elimination of DNA and reveal that PGR is completed over the course of several successive cell divisions.

No MeSH data available.


Related in: MedlinePlus

Morphology of anaphase lagging chromatin in intact embryonic cells.Immunolabeling and hybridization of intact, PACT-cleared, embryos (2 dpf). (A) immunolabeling with anti-beta-tubulin, lagging chromatin is oriented along the polar microtubules. (B) Confocal image of an anaphase labeled with a centromere specific probe (Cot1 FISH). Centromeres of lagging chromosomes are oriented toward the poles of mitotic spindle. (C) Confocal image of an anaphase from an embryo at 1dpf: lagging chromosomes form equatorial contacts, bridging between the poles of the mitotic spindle. (D) An anaphase with multiple bridging chromosomes, hybridized with a probe to repetitive DNA (Cot2 FISH). Punctate signals corresponding to centromeres are oriented toward the spindle poles but lag behind retained chromosomes. Sites of apparent contact between sister chromatids hybridize strongly to Cot2 DNA, suggesting that repetitive DNA may participate in establishing these contacts. (E) Fluorescence in situ hybridization of the Germ1 probe to an anaphase with several bridging chromosomes. Germ1 signals are symmetrical, further supporting the interpretation that bridging features consist of pairs of sister chromatids, though notably, Germ1 signals do not appear to overlap with the zone of contact between sister chromatids.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4920378&req=5

pgen.1006103.g004: Morphology of anaphase lagging chromatin in intact embryonic cells.Immunolabeling and hybridization of intact, PACT-cleared, embryos (2 dpf). (A) immunolabeling with anti-beta-tubulin, lagging chromatin is oriented along the polar microtubules. (B) Confocal image of an anaphase labeled with a centromere specific probe (Cot1 FISH). Centromeres of lagging chromosomes are oriented toward the poles of mitotic spindle. (C) Confocal image of an anaphase from an embryo at 1dpf: lagging chromosomes form equatorial contacts, bridging between the poles of the mitotic spindle. (D) An anaphase with multiple bridging chromosomes, hybridized with a probe to repetitive DNA (Cot2 FISH). Punctate signals corresponding to centromeres are oriented toward the spindle poles but lag behind retained chromosomes. Sites of apparent contact between sister chromatids hybridize strongly to Cot2 DNA, suggesting that repetitive DNA may participate in establishing these contacts. (E) Fluorescence in situ hybridization of the Germ1 probe to an anaphase with several bridging chromosomes. Germ1 signals are symmetrical, further supporting the interpretation that bridging features consist of pairs of sister chromatids, though notably, Germ1 signals do not appear to overlap with the zone of contact between sister chromatids.

Mentions: Within a cell cycle, eliminated chromatin is first identifiable as thread-like structures that are situated between groups of poleward-oriented chromosomes immediately after the metaphase/anaphase transition. As anaphase progresses, eliminated material begins to exhibit distinguishable differences in its apparent motion relative to retained chromosomes. Lagging chromatin is typically oriented parallel to the interpolar microtubules and appeared to be tightly associated with spindle filaments (Fig 4A; S4 Fig). As cells enter telophase, retained sister chromatids begin to decondense and adopt lobate structures consistent with decondensation of somatic chromosomes and recruitment of nuclear envelope proteins. Notably, lagging chromatin does not appear to decondense at this same time and associates with tubulin prior to being packaged into compact MNi (S4 Fig and S5 Fig).


Cellular and Molecular Features of Developmentally Programmed Genome Rearrangement in a Vertebrate (Sea Lamprey: Petromyzon marinus).

Timoshevskiy VA, Herdy JR, Keinath MC, Smith JJ - PLoS Genet. (2016)

Morphology of anaphase lagging chromatin in intact embryonic cells.Immunolabeling and hybridization of intact, PACT-cleared, embryos (2 dpf). (A) immunolabeling with anti-beta-tubulin, lagging chromatin is oriented along the polar microtubules. (B) Confocal image of an anaphase labeled with a centromere specific probe (Cot1 FISH). Centromeres of lagging chromosomes are oriented toward the poles of mitotic spindle. (C) Confocal image of an anaphase from an embryo at 1dpf: lagging chromosomes form equatorial contacts, bridging between the poles of the mitotic spindle. (D) An anaphase with multiple bridging chromosomes, hybridized with a probe to repetitive DNA (Cot2 FISH). Punctate signals corresponding to centromeres are oriented toward the spindle poles but lag behind retained chromosomes. Sites of apparent contact between sister chromatids hybridize strongly to Cot2 DNA, suggesting that repetitive DNA may participate in establishing these contacts. (E) Fluorescence in situ hybridization of the Germ1 probe to an anaphase with several bridging chromosomes. Germ1 signals are symmetrical, further supporting the interpretation that bridging features consist of pairs of sister chromatids, though notably, Germ1 signals do not appear to overlap with the zone of contact between sister chromatids.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920378&req=5

pgen.1006103.g004: Morphology of anaphase lagging chromatin in intact embryonic cells.Immunolabeling and hybridization of intact, PACT-cleared, embryos (2 dpf). (A) immunolabeling with anti-beta-tubulin, lagging chromatin is oriented along the polar microtubules. (B) Confocal image of an anaphase labeled with a centromere specific probe (Cot1 FISH). Centromeres of lagging chromosomes are oriented toward the poles of mitotic spindle. (C) Confocal image of an anaphase from an embryo at 1dpf: lagging chromosomes form equatorial contacts, bridging between the poles of the mitotic spindle. (D) An anaphase with multiple bridging chromosomes, hybridized with a probe to repetitive DNA (Cot2 FISH). Punctate signals corresponding to centromeres are oriented toward the spindle poles but lag behind retained chromosomes. Sites of apparent contact between sister chromatids hybridize strongly to Cot2 DNA, suggesting that repetitive DNA may participate in establishing these contacts. (E) Fluorescence in situ hybridization of the Germ1 probe to an anaphase with several bridging chromosomes. Germ1 signals are symmetrical, further supporting the interpretation that bridging features consist of pairs of sister chromatids, though notably, Germ1 signals do not appear to overlap with the zone of contact between sister chromatids.
Mentions: Within a cell cycle, eliminated chromatin is first identifiable as thread-like structures that are situated between groups of poleward-oriented chromosomes immediately after the metaphase/anaphase transition. As anaphase progresses, eliminated material begins to exhibit distinguishable differences in its apparent motion relative to retained chromosomes. Lagging chromatin is typically oriented parallel to the interpolar microtubules and appeared to be tightly associated with spindle filaments (Fig 4A; S4 Fig). As cells enter telophase, retained sister chromatids begin to decondense and adopt lobate structures consistent with decondensation of somatic chromosomes and recruitment of nuclear envelope proteins. Notably, lagging chromatin does not appear to decondense at this same time and associates with tubulin prior to being packaged into compact MNi (S4 Fig and S5 Fig).

Bottom Line: Programmed genome rearrangements (PGRs) result in the reproducible loss of ~20% of the genome from somatic cell lineages during early embryogenesis.Here we identify epigenetic silencing events that are associated with the programmed elimination of DNA and describe the spatiotemporal dynamics of PGR during lamprey embryogenesis.During early embryogenesis a majority of micronuclei (~60%) show strong enrichment for repressive chromatin modifications (H3K9me3 and 5meC).

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Kentucky, Lexington, Kentucky, United States of America.

ABSTRACT
The sea lamprey (Petromyzon marinus) represents one of the few vertebrate species known to undergo large-scale programmatic elimination of genomic DNA over the course of its normal development. Programmed genome rearrangements (PGRs) result in the reproducible loss of ~20% of the genome from somatic cell lineages during early embryogenesis. Studies of PGR hold the potential to provide novel insights related to the maintenance of genome stability during the cell cycle and coordination between mechanisms responsible for the accurate distribution of chromosomes into daughter cells, yet little is known regarding the mechanistic basis or cellular context of PGR in this or any other vertebrate lineage. Here we identify epigenetic silencing events that are associated with the programmed elimination of DNA and describe the spatiotemporal dynamics of PGR during lamprey embryogenesis. In situ analyses reveal that the earliest DNA methylation (and to some extent H3K9 trimethylation) events are limited to specific extranuclear structures (micronuclei) containing eliminated DNA. During early embryogenesis a majority of micronuclei (~60%) show strong enrichment for repressive chromatin modifications (H3K9me3 and 5meC). These analyses also led to the discovery that eliminated DNA is packaged into chromatin that does not migrate with somatically retained chromosomes during anaphase, a condition that is superficially similar to lagging chromosomes observed in some cancer subtypes. Closer examination of "lagging" chromatin revealed distributions of repetitive elements, cytoskeletal contacts and chromatin contacts that provide new insights into the cellular mechanisms underlying the programmed loss of these segments. Our analyses provide additional perspective on the cellular and molecular context of PGR, identify new structures associated with elimination of DNA and reveal that PGR is completed over the course of several successive cell divisions.

No MeSH data available.


Related in: MedlinePlus