Laan, L. | Search bioRxiv

bioRxiv2017

Chromosome loss rate in cells of different ploidy can be explained by spindle self-organization

The mitotic spindle segregates chromosomes and minimizes chromosome loss for the specific number of chromosomes present in an organism. In Saccharomyces cerevisiae, for example, haploid and diploid cells are part of the sexual life cycle and have a thousand times lower rate of chromosome loss than tetraploid cells. Currently it is unclear what constrains the number of chromosomes that can be segregated with high fidelity in an organism. Here we developed a mathematical model to study if different rates of chromosome loss in cells with different ploidy can arise from changes in (1) spindle dynamics and (2) a maximum duration of mitotic arrest, after which cells enter anaphase. Our model reveals how small increases in spindle assembly time can result in exponential differences in rate of chromosomes loss between cells of increasing ploidy and predicts the maximum duration of mitotic arrest.

evolutionary biology↗

bioRxiv2017

Patterns of conservation and diversification in the fungal polarization network

The combined actions of proteins in networks underlie all fundamental cellular functions. Deeper insights into the dynamics of network composition across species and their functional consequences are crucial to fully understand protein network evolution. Large-scale comparative studies with high phylogenetic resolution are now feasible through the recent rise in available genomic datasets of both model and non-model species. Here we focus on the polarity network, which is universally essential for cell proliferation and studied in great detail in the model organism, Saccharomyces cerevisiae. We examine 34 proteins, directly related to cell polarization, across 200 fungal strains/species to determine evolution of the composition of the network and patterns of conservation and diversification.\n\nWe observe strong protein conservation for a group of 16 core proteins: 95% of all strains/species possess at least 75% of these proteins, albeit in varying compositions. We find high levels of variation in prevalence and sequence identity in the remaining 18 proteins, resulting in distinct lineage-specific compositions of the network in the majority of strains/species. We test if the observed diversification in network composition correlates with potential underlying factors and find that lineage, lifestyle, and genetic distance co-vary with network size. Yeast, filamentous and basal unicellular fungi form distinctive groups based on these analyses, with substantial differences to their polarization network. Our study shows that evolution of the fungal polarization network is highly dynamic, even between closely related species, and that functional conservation is achieved by varying structural conservation of the fungal polarization proteins.\n\nData DepositionSequence alignments used are available upon request.

evolutionary biology↗