Biology subjects

Hernandez-Armendariz, A.

Publications and source records attributed to Hernandez-Armendariz, A..

3 recordsLinked to original sources

bioRxiv2025

Ki-67 shapes the nucleolus by anchoring chromatin via its amphiphilic properties

The nucleolus, a membrane-less organelle essential for ribosome biogenesis, adopts variable shapes across cell types and in response to environmental conditions, yet the mechanisms regulating its morphology and functional implications remain unclear. Using a high-throughput screen, we identify the proliferation marker Ki-67 as a central regulator of nucleolar shape. Ki-67 localises to the chromatinnucleolus interface, where its depletion induces nucleolar rounding and reduces chromatin enrichment within and around the nucleolus. This effect is driven by amphiphilic properties conferred by two distinct affinity domains separated by a spacer. Given that chromatin loss is a common feature of rounded nucleoli in our screen, and acute chromatin digestion also induces rounding, we propose that the chromatin environment in and around the nucleolus plays a key role in determining nucleolar shape. Our study elucidates a novel Ki-67-mediated chromatin anchoring mechanism, tightly linking nucleolar shape to genome organisation and expanding our understanding of condensate morphology.

cell biology↗

bioRxiv2024

Charge distribution of coating brush drives inter-chromosome attraction

The condensation of charged polymers is an important driver for the formation of biomolecular condensates. Recent experiments suggest that this mechanism also controls the clustering of eukaryotic chromosomes during the late stages of cell division. In this process, inter-chromosome attraction is driven by the condensation of cytoplasmic RNA and Ki-67, a charged intrinsically disordered protein that coats the chromosomes as a brush. Attraction between chromosomes has been shown to be specifically promoted by a localized charged patch on Ki-67, although the physical mechanism remains unclear. To elucidate this process, we combine here coarse-grained simulations and analytical theory to study the RNA-mediated interaction between charged polymer brushes on the chromosome surfaces. We show that the charged patch on Ki-67 leads to inter-chromosome attraction via RNA bridging between the two brushes, whereby the RNA preferentially interacts with the charged patches, leading to stable, long-range forces. By contrast, if the brush is uniformly charged, bridging is basically absent due to complete adsorption of RNA onto the brush. Moreover, the RNA dynamics becomes caged in presence of the charged patch, while remaining diffusive with uniform charge. Our work sheds light on the physical origin of chromosome clustering, while also suggesting a general mechanism for cells to tune work production by biomolecular condensates via different charge distributions.

biophysics↗

bioRxiv2023

A liquid-like coat mediates chromosome clustering during mitotic exit

SummaryThe individualization of chromosomes during early mitosis and their clustering upon exit from cell division are two key transitions that ensure efficient segregation of eukaryotic chromosomes. Both processes are regulated by the surfactant-like protein Ki-67, but how Ki-67 achieves these diametric functions has remained unknown. Here, we report that Ki-67 radically switches from a chromosome repellent to a chromosome attractant during anaphase. We show that Ki-67 dephosphorylation during mitotic exit and the simultaneous exposure of a conserved basic patch induce the RNA-dependent formation of a liquid-like condensed phase on the chromosome surface. Experiments and coarse-grained simulations support a model in which the coalescence of chromosome surfaces driven by phase separation promote clustering of chromosomes. Our study reveals how the switch of Ki-67 from a surfactant to a liquid-like condensed phase can generate the mechanical forces during genome segregation that are required for re-establishing nuclear-cytoplasmic compartmentalization after mitosis.

cell biology↗