Biology subjects

Eykelenboom, J. K.

Publications and source records attributed to Eykelenboom, J. K..

4 recordsLinked to original sources

bioRxiv2025

Contractile peri-nuclear actomyosin network PANEM repositions chromosomes from unfavorable locations to facilitate their interaction with the mitotic spindle

Chromosomes must efficiently and properly interact with the mitotic spindle during prometaphase for correct segregation in anaphase. Chromosomes at the nuclear periphery or behind the spindle poles interact less efficiently with the mitotic spindle, increasing the risk of missegregation. The mechanisms that mitigate such risks in unperturbed cells are unknown. An actomyosin network (PANEM) forms around the nucleus during prophase. While the myosin-II-dependent PANEM contraction immediately after nuclear envelope breakdown (NEBD) facilitates chromosome interaction with the mitotic spindle, the mechanism by which it does so remains unclear. Here, using human cell lines, we show that immediately after NEBD, PANEM contraction directly pushes chromosomes at the nuclear periphery or behind spindle poles toward the center of cells. Detailed tracking of kinetochore movements following light-induced activation of a myosin-II inhibitor reveals that this inward movement of chromosomes facilitates kinetochores initial interaction with spindle microtubules. It also promotes the onset of kinetochores congression towards the spindle mid-plane, but not congression itself once it starts. Thus, PANEM contraction ensures high-fidelity chromosome segregation by relocating chromosomes from unfavorable locations. Since some chromosomally unstable cancer cells fail to establish PANEM during early mitosis, the absence of PANEM may contribute to numerical chromosomal instability in these cells. Impact statementAn actomyocin network (PANEM) forms around the nucleus in prophase, and its contraction repositions peripheral and polar chromosomes to facilitate their interaction with the mitotic spindle, ensuring their correct segregation.

cell biology↗

bioRxiv2024

Exclusion of condensin I from the nucleus during prophase coordinates mitotic chromosome reorganization to complete sister chromatid resolution

AbstractDuring early mitosis, chromosomes are reorganized from their relatively decompacted interphase state into characteristic mitotic rod-shaped structures. This process is important to allow correct segregation of newly replicated sister chromatids to the opposite spindle poles during anaphase. To facilitate mitotic chromosome organization, two protein complexes named condensin I and condensin II play crucial roles. Condensin II is particularly important for achieving sister chromatid separation (resolution) whilst condensin I is required for chromosome condensation (compaction). Although sister chromatid resolution occurs 15-20 min earlier before chromosome compaction, it is not yet clear how these events are temporally coordinated or whether this temporal coordination is important to ensure chromosome segregation later in mitosis. One hypothesis is that the temporal coordination is achieved through different subcellular localisation of two condensin complexes; whilst condensin II localizes in the nucleus, condensin I is restricted to the cytoplasm, during interphase and prophase. In this study we tested this hypothesis by engineering the localization of condensin I to the nucleus. We monitored sister chromatid resolution and chromosome compaction by real-time imaging that visualized selected neighboring chromosome loci. We found that localization of condensin I to the nucleus led to precocious chromosome compaction during prophase with a similar timing to sister chromatid resolution. We also monitored later stages of mitosis and found that cells expressing nuclear condensin I subsequently exhibited frequent chromosome mis-segregation in anaphase. Therein, the majority of mis-segregated chromosomes consisted of lagging chromosomes involving both sister chromatids. This suggests that the temporal control of mitotic chromosome reorganization is crucial for high-fidelity chromosome segregation. In conclusion, the exclusion of condensin I from the nucleus during prophase delays chromosome compaction and allows condensin II to complete sister chromatid resolution, which ensures correct chromosome segregation later in mitosis.

cell biology↗

bioRxiv2018

Contractile actomyosin network on nuclear envelope remnants positions chromosomes for mitosis

To ensure proper segregation during mitosis, chromosomes must be efficiently captured by kinetochore microtubules and subsequently aligned on the mitotic spindle. The efficacy of chromosome capture by the mitotic spindle can be influenced by how widely chromosomes are scattered in space. Here, we quantify chromosome-scattering volume (CSV) and find that it is reduced immediately after nuclear envelope breakdown (NEBD) in human cells. The reduction of CSV occurs independently of microtubules and is therefore not an outcome of interactions between chromosomes and the spindle. We find that, prior to NEBD, an acto-myosin network is assembled in a LINC complex-dependent manner on the cytoplasmic surface of the nuclear envelope. This acto-myosin network remains around chromosomes soon after NEBD, and its myosin-II-mediated contraction reduces CSV and facilitates chromosome interaction with spindle microtubules.

cell biology↗

bioRxiv2018

Live-cell imaging of marked chromosome regions reveals dynamics of mitotic chromosome resolution and compaction

When human cells enter mitosis, chromosomes undergo substantial changes in their organisation to resolve sister chromatids and compact chromosomes. Despite the fundamental importance of this phenomenon to genome stability, we still do not fully comprehend the timing and coordination of these events. To address these questions, we need to evaluate the progression of both sister chromatid resolution and chromosome compaction in one assay. We achieved this by analysing changes in configuration of marked chromosome regions over time, with high spatial and temporal resolution. This assay showed that sister chromatid resolution is an iterative process that begins in late G2 phase and completes in prophase. Cohesins and WAPL antagonistically regulate sister chromatid resolution in late G2 and prophase whilst local enrichment of cohesin on chromosomes prevents precocious sister chromatid resolution. Moreover, our assay allowed quantitative evaluation of the timing and efficiency of condensin II and I activities in promoting sister chromatid resolution and chromosome compaction, respectively. Thus, our real-time assay sheds new light on the dynamics of mitotic chromosome resolution and compaction.

cell biology↗