ORCID Profile
0000-0002-3596-9407
Current Organisation
The University of Edinburgh
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Publisher: Springer Science and Business Media LLC
Date: 08-11-2022
DOI: 10.1038/S41467-022-34294-6
Abstract: Human beings are made of ~50 trillion cells which arise from serial mitotic isions of a single cell - the fertilised egg. Remarkably, the early human embryo is often chromosomally abnormal, and many are mosaic, with the karyotype differing from one cell to another. Mosaicism presumably arises from chromosome segregation errors during the early mitotic isions, although these events have never been visualised in living human embryos. Here, we establish live cell imaging of chromosome segregation using normally fertilised embryos from an egg-share-to-research programme, as well as embryos deselected during fertility treatment. We reveal that the first mitotic ision has an extended prometaphase/metaphase and exhibits phenotypes that can cause nondisjunction. These included multipolar chromosome segregations and lagging chromosomes that lead to formation of micronuclei. Analysis of nuclear number and size provides evidence of equivalent phenotypes in 2-cell human embryos that gave rise to live births. Together this shows that errors in the first mitotic ision can be tolerated in human embryos and uncovers cell biological events that contribute to preimplantation mosaicism.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 27-02-2004
Abstract: During meiosis, two chromosome segregation phases follow a single round of DNA replication. We identified factors required to establish this specialized cell cycle by examining meiotic chromosome segregation in a collection of yeast strains lacking all nonessential genes. This analysis revealed Sgo1, Chl4, and Iml3 to be important for retaining centromeric cohesin until the onset of anaphase II. Consistent with this role, Sgo1 localizes to centromeric regions but dissociates at the onset of anaphase II. The screen described here provides a comprehensive analysis of the genes required for the meiotic cell cycle and identifies three factors important for the stepwise loss of sister chromatid cohesion.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 10-03-2017
Abstract: Although much effort has been devoted to studying yeast in the past few decades, our understanding of this model organism is still limited. Rapidly developing DNA synthesis techniques have made a “build-to-understand” approach feasible to reengineer on the genome scale. Here, we report on the completion of a 770-kilobase synthetic yeast chromosome II (synII). SynII was characterized using extensive Trans-Omics tests. Despite considerable sequence alterations, synII is virtually indistinguishable from wild type. However, an up-regulation of translational machinery was observed and can be reversed by restoring the transfer RNA (tRNA) gene copy number. Following the “design-build-test-debug” working loop, synII was successfully designed and constructed in vivo. Extensive Trans-Omics tests were conducted, including phenomics, transcriptomics, proteomics, metabolomics, chromosome segregation, and replication analyses. By both complementation assays and SCRaMbLE (synthetic chromosome rearrangement and modification by loxP -mediated evolution), we targeted and debugged the origin of a growth defect at 37°C in glycerol medium. To efficiently construct megabase-long chromosomes, we developed an I- Sce I–mediated strategy, which enables parallel integration of synthetic chromosome arms and reduced the overall integration time by 50% for synII. An I- Sce I site is introduced for generating a double-strand break to promote targeted homologous recombination during mitotic growth. Despite hundreds of modifications introduced, there are still regions sharing substantial sequence similarity that might lead to undesirable meiotic recombinations when intercrossing the two semisynthetic chromosome arm strains. Induction of the I- Sce I–mediated double-strand break is otherwise lethal and thus introduced a strong selective pressure for targeted homologous recombination. Since our strategy is designed to generate a markerless synII and leave the URA3 marker on the wild-type chromosome, we observed a tenfold increase in URA3 -deficient colonies upon I- Sce I induction, meaning that our strategy can greatly bias the crossover events toward the designated regions. By incorporating comprehensive phenotyping approaches at multiple levels, we demonstrated that synII was capable of powering the growth of yeast indistinguishably from wild-type cells (see the figure), showing highly consistent biological processes comparable to the native strain. Meanwhile, we also noticed modest but potentially significant up-regulation of the translational machinery. The main alteration underlying this change in expression is the deletion of 13 tRNA genes. A growth defect was observed in one very specific condition—high temperature (37°C) in medium with glycerol as a carbon source—where colony size was reduced significantly. We targeted and debugged this defect by two distinct approaches. The first approach involved phenotype screening of all intermediate strains followed by a complementation assay with wild-type sequences in the synthetic strain. By doing so, we identified a modification resulting from PCRTag recoding in TSC10 , which is involved in regulation of the yeast high-osmolarity glycerol (HOG) response pathway. After replacement with wild-type TSC10 , the defect was greatly mitigated. The other approach, debugging by SCRaMbLE, showed rearrangements in regions containing HOG regulation genes. Both approaches indicated that the defect is related to HOG response dysregulation. Thus, the phenotypic defect can be pinpointed and debugged through multiple alternative routes in the complex cellular interactome network. We have demonstrated that synII segregates, replicates, and functions in a highly similar fashion compared with its wild-type counterpart. Furthermore, we believe that the iterative “design-build-test-debug” cycle methodology, established here, will facilitate progression of the Sc2.0 project in the face of the increasing synthetic genome complexity. ( A ) Cell cycle comparison between synII and BY4741 revealed by the percentage of cells with separated CEN2-GFP dots, metaphase spindles, and anaphase spindles. ( B ) Replication profiling of synII (red) and BY4741 (black) expressed as relative copy number by deep sequencing. ( C ) RNA sequencing analysis revealed that the significant up-regulation of translational machinery in synII is induced by the deletion of tRNA genes in synII.
Publisher: Elsevier BV
Date: 11-1999
DOI: 10.1016/S1097-2765(00)80378-0
Abstract: The Spo0J and Soj proteins of B. subtilis belong to a widespread family of bacterial proteins required for accurate segregation of plasmids and chromosomes. Spo0J binds to several sites around the oriC region of the chromosome, which are organized into compact foci that may play a centromere-like role in active chromosome segregation. We now show that Soj has a role in organization or compaction of Spo0J-oriC complexes and possibly other regions of the nucleoid. This activity is accompanied by a dynamic localization pattern in which Soj protein undergoes assembly and disassembly into large nucleoid-associated patches on a timescale of minutes. The dynamic behavior of Soj, like its previously described transcriptional repression activity, is controlled by Spo0J. These interactions may constitute a checkpoint coupling developmental transcription to cell cycle progression.
Publisher: Wiley
Date: 07-1999
DOI: 10.1046/J.1365-2958.1999.01450.X
Abstract: Bacterial cell ision commences with the assembly of the tubulin-like protein, FtsZ, at midcell to form a ring. Division site selection in rod-shaped bacteria is mediated by MinC and MinD, which form a ision inhibitor. Bacillus subtilis DivIVA protein ensures that MinCD specifically inhibits ision close to the cell poles, while allowing ision at midcell. We have examined the localization of MinC protein and show that it is targeted to midcell and retained at the mature cell poles. This localization is reminiscent of the pattern previously described for MinD. Localization of MinC requires both early (FtsZ) and late (PbpB) ision proteins, and it is completely dependent on MinD. The effects of a IVA mutation on localization of MinC now suggest that the main role of DivIVA is to retain MinCD at the cell poles after ision, rather than recruitment to nascent ision sites. By overexpressing minC or minD, we show that both proteins are required to block ision, but that only MinD needs to be in excess of wild-type levels. The results suggest a mechanism whereby MinD is required both to pilot MinC to the cell poles and to constitute a functional ision inhibitor.
Publisher: Cold Spring Harbor Laboratory
Date: 11-1998
Abstract: Cell ision in rod-shaped bacteria is initiated by formation of a ring of the tubulin-like protein FtsZ at mid-cell. Division site selection is controlled by a conserved ision inhibitor MinCD, which prevents aberrant ision at the cell poles. The Bacillus subtilis DivIVA protein controls the topological specificity of MinCD action. Here we show that DivIVA is targeted to ision sites late in their assembly, after some MinCD-sensitive step requiring FtsZ and other ision proteins has been passed. DivIVA then recruits MinD to the ision sites preventing another ision from taking place near the newly formed cell poles. Sequestration of MinD to the poles also releases the next mid-cell sites for ision. Remarkably, this mechanism of DivIVA action is completely different from that of the equivalent protein MinE of Escherichia coli , even though both systems operate via the same ision inhibitor MinCD.
Publisher: Cold Spring Harbor Laboratory
Date: 14-01-2023
DOI: 10.1101/2023.01.13.523952
Abstract: Aneuploid human eggs (oocytes) are a major cause of infertility, miscarriage and chromosomal disorders. Such aneuploidies increase greatly as women age, originating from defective linkages between sister-chromatids (cohesion) in meiosis. We found evidence that loss of a specific pool of the cohesin protector protein, shugoshin 2 (Sgo2) contributes to this phenomenon. Our data indicate that Sgo2 preserves sister chromatid cohesion in meiosis by protecting a ‘cohesin bridge’ between sister chromatids. In human oocytes, Sgo2 localizes to both sub-centromere cups and the pericentromeric bridge which spans the sister chromatid junction. Sgo2 normally colocalizes with cohesin, however, in oocytes from older women, Sgo2 is frequently lost specifically from the pericentromeric bridge and sister chromatid cohesion is weakened. Mps1 and Bub1 kinase activities maintain Sgo2 at sub-centromeres and the pericentromeric bridge. Removal of Sgo2 throughout meiosis I by Mps1 inhibition reduces cohesion protection, increasing the incidence of single chromatids at meiosis II. Therefore, Sgo2 deficiency in human oocytes can exacerbate the effects of maternal age by rendering residual cohesin at pericentromeres vulnerable to loss in anaphase I. Our data show that maternal age-dependent loss of Sgo2 at the pericentromere bridge in human oocytes impairs cohesion integrity and contributes to the increased incidence of aneuploidy observed in human oocytes with advanced maternal age.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Adele Marston.