Biology subjects

Nilsson, J.

Publications and source records attributed to Nilsson, J..

4 recordsLinked to original sources

bioRxiv2018

The RZZ complex facilitates Mad1 binding to Bub1 ensuring efficient checkpoint signaling

Introductory paragraphThe recruitment of Mad1 to unattached kinetochores is essential for generating a \"wait anaphase\" signal during mitosis yet Mad1 localization is poorly understood in mammalian cells. In yeast the Bub1 checkpoint protein is the sole Mad1 receptor but in mammalian cells the Rod-ZW10-Zwilch (RZZ) complex is also required for Mad1 kinetochore localization. The exact function of the two mammalian Mad1 receptors and whether there is any interplay between them is unclear. Here we use CRISPR genome editing to generate RNAi sensitized human cell lines revealing a strong requirement for both Rod and Bub1 in checkpoint signaling. We show that the RZZ complex facilitates Mad1 binding to Bub1 and that a region of Bub1 overlapping the Mad1 binding site stimulates RZZ kinetochore recruitment. The requirement for RZZ in the checkpoint, but not Bub1, can be bypassed by tethering Mad1 to kinetochores or by increasing the strength of the Bub1-Mad1 interaction. Our data support a model in which the primary role of RZZ is to localize Mad1 at kinetochores allowing for the efficient checkpoint generating Mad1-Bub1 interaction. As such, the core checkpoint principle is conserved from yeast to man.

cell biology↗

bioRxiv2018

The closed form of Mad2 is bound to Mad1 and Cdc20 at unattached kinetochores

The spindle assembly checkpoint (SAC) ensures accurate chromosome segregation by delaying anaphase onset in response to unattached kinetochores. Anaphase is delayed by the generation of the mitotic checkpoint complex (MCC) composed of the checkpoint proteins Mad2 and BubR1/Bub3 bound to the protein Cdc20. Current models assume that MCC production is catalyzed at unattached kinetochores and that the Mad1/Mad2 complex is instrumental in the conversion of Mad2 from an open form (O-Mad2) to a closed form (C-Mad2) that can bind to Cdc20. Importantly the levels of Mad2 at kinetochores correlate with SAC activity but whether C-Mad2 at kinetochores exclusively represents its complex with Mad1 is not fully established. Here we use a recently established C-Mad2 specific monoclonal antibody to show that Cdc20 and C-Mad2 levels correlate at kinetochores and that depletion of Cdc20 reduces Mad2 but not Mad1 kinetochore levels. Importantly reintroducing wild type Cdc20 but not Cdc20 R132A, a mutant form that cannot bind Mad2, restores Mad2 levels. In agreement with this live cell imaging of fluorescent tagged Mad2 reveals that Cdc20 depletion strongly reduces Mad2 localization to kinetochores. These results support the presence of Mad2-Cdc20 complexes at kinetochores in agreement with current models of the SAC but also argue that Mad2 levels at kinetochores cannot be used as a direct readout of Mad1 levels.

cell biology↗

bioRxiv2017

Working memory and reasoning tasks are associated with different modes of large-scale brain dynamics in healthy older adults

Researchers have proposed that solving complex reasoning problems, a key indicator of fluid intelligence, involves the same cognitive processes as solving working memory tasks. This proposal is supported by an overlap of the functional brain activations associated with the two types of tasks and by high correlations between inter-individual differences in performance. We replicated these findings in fifty-three older subjects but also showed that solving reasoning and working memory problems benefits from different configurations of the functional connectome and that this dissimilarity increases with higher difficulty load. Specifically, superior performance in a typical working memory paradigm (n-back) was associated with up-regulation of modularity (increased between-network segregation), whereas performance in the reasoning task was associated with effective down-regulation of modularity. We also showed that working memory training promotes task-invariant increases in modularity. Since superior reasoning performance is associated with down-regulation of modular dynamics, training may thus have fostered an inefficient way of solving the reasoning tasks. This could help explain why working memory training does little to promote complex reasoning performance. The study concludes that complex reasoning abilities cannot be reduced to working memory and suggests the need to reconsider the feasibility of using working memory training interventions to attempt to achieve effects that transfer to broader cognition.

neuroscience↗

bioRxiv2017

Regulation of mesenchymal stem cell function by TGFβ-1 on mast cell extracellular vesicles -- role of endosomal retention

Extracellular vesicles (EVs) convey biological messages between cells, either by surface-to-surface interaction, or by shuttling of bioactive molecules to a recipient cell cytoplasm. Here we show that EVs released by human primary mast cells or transformed human mast cells (HMC1), carry TGF{beta}-1 on their surface. EV-associated TGF{beta}-1 enhance the migratory activity of human mesenchymal stem cells (MSCs) compared to free TGF{beta}-1, as both knockdown of TGF{beta}, or a TGF{beta}-antibody, attenuate the effect. The MSCs respond by increasing matrix metalloproteinase-2 and -9 (MMP) activity. Further, EVs given to MSCs are retained in the endosomal compartments at a time of biological function, prolonging EV-associated TGF{beta}-1 signaling vs free TGF{beta}-1. When exposed to EVs, MSCs home more toward allergen-exposed lung in a mouse allergen model, resulting in attenuated allergic inflammation. Our results show that mast cell-EVs are decorated with TGFb-1, are retained in endosomes, which influences both MSC phenotype and function.

cell biology↗