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Chromosomes trapped in micronuclei are liable to segregation errors.

ABSTRACT: DNA in micronuclei is likely to get damaged. When shattered DNA from micronuclei gets reincorporated into the primary nucleus, aberrant rearrangements can take place, a phenomenon referred to as chromothripsis. Here, we investigated how chromatids from micronuclei act in subsequent divisions and how this affects their fate. We observed that the majority of chromatids derived from micronuclei fail to establish a proper kinetochore in mitosis, which is associated with problems in chromosome alignment, segregation and spindle assembly checkpoint activation. Remarkably, we found that, upon their formation, micronuclei already display decreased levels of important kinetochore assembly factors. Importantly, these defects favour the exclusion of the micronucleus over the reintegration into the primary nucleus over several divisions. Interestingly, the defects observed in micronuclei are likely overcome once micronuclei are reincorporated into the primary nuclei, as they further propagate normally. We conclude that the formation of a separate small nuclear entity represents a mechanism for the cell to delay the stable propagation of excess chromosome(s) and/or damaged DNA, by inducing kinetochore defects.

SUBMITTER: Soto M

PROVIDER: S-EPMC6051344 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Chromosomes trapped in micronuclei are liable to segregation errors.

Soto Mar M García-Santisteban Iraia I Krenning Lenno L Medema René H RH Raaijmakers Jonne A JA

Journal of cell science 20180709 13

DNA in micronuclei is likely to get damaged. When shattered DNA from micronuclei gets reincorporated into the primary nucleus, aberrant rearrangements can take place, a phenomenon referred to as chromothripsis. Here, we investigated how chromatids from micronuclei act in subsequent divisions and how this affects their fate. We observed that the majority of chromatids derived from micronuclei fail to establish a proper kinetochore in mitosis, which is associated with problems in chromosome alignm ...[more]

PMID: 29930083

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Project description:In most organisms, cells typically maintain genome integrity, as radical genome reorganization leads to dramatic consequences. However, certain organisms, ranging from unicellular ciliates to vertebrates, are able to selectively eliminate specific parts of their genome during certain stages of development. Moreover, partial or complete elimination of one of the parental genomes occurs in interspecies hybrids reproducing asexually. Although several examples of this phenomenon are known, the molecular and cellular processes involved in selective elimination of genetic material remain largely undescribed for the majority of such organisms. Here, we elucidate the process of selective genome elimination in water frog hybrids from the Pelophylax esculentus complex reproducing through hybridogenesis. Specifically, in the gonads of diploid and triploid hybrids, but not those of the parental species, we revealed micronuclei in the cytoplasm of germ cells. In each micronucleus, only one centromere was detected with antibodies against kinetochore proteins, suggesting that each micronucleus comprises a single chromosome. Using 3D-FISH with species-specific centromeric probe, we determined the role of micronuclei in selective genome elimination. We found that in triploid LLR hybrids, micronuclei preferentially contain P. ridibundus chromosomes, while in diploid hybrids, micronuclei preferentially contain P. lessonae chromosomes. The number of centromere signals in the nuclei suggested that germ cells were aneuploid until they eliminate the whole chromosomal set of one of the parental species. Furthermore, in diploid hybrids, misaligned P. lessonae chromosomes were observed during the metaphase stage of germ cells division, suggesting their possible elimination due to the inability to attach to the spindle and segregate properly. Additionally, we described gonocytes with an increased number of P. ridibundus centromeres, indicating duplication of the genetic material. We conclude that selective genome elimination from germ cells of diploid and triploid hybrids occurs via the gradual elimination of individual chromosomes of one of the parental genomes, which are enclosed within micronuclei.

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Chromosomes trapped in micronuclei are liable to segregation errors.

Publications

Chromosomes trapped in micronuclei are liable to segregation errors.

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