Biology subjects

Curran, S.

Publications and source records attributed to Curran, S..

2 recordsLinked to original sources

bioRxiv2023

The Host Adapted Fungal Pathogens of Pneumocystis Genus Utilize Genic Regional Centromeres

Centromeres are constricted chromosomal regions that are essential for cell division. In eukaryotes, centromeres display a remarkable architectural and genetic diversity. The basis of centromere accelerated evolution remains elusive. Here we focused on Pneumocystis species, a group of Mammalian-specific fungal pathogens that form a sister taxon with that of the Schizosaccharomyces pombe, an important genetic model for centromere biology research. Methods allowing reliable continuous culture of Pneumocystis species do not currently exist, precluding genetic manipulation. CENP-A, a variant of histone H3, is the epigenetic marker that defines centromeres in most eukaryotes. Using heterologous complementation, we show that the Pneumocystis CENP-A ortholog is functionally equivalent to CENP-ACnp1 of Schizosaccharomyces pombe. Using organisms from a short-term in vitro culture or infected animal models and ChIP-Seq, we identified CENP-A bound regions in two Pneumocystis species that diverged [~]35 million years ago. Each species has a unique short regional centromere (< 10kb) flanked by heterochromatin in 16-17 monocentric chromosomes. They span active genes and lack conserved DNA sequence motifs and repeats. These features suggest an epigenetic specification of centromere function. Analysis of centromeric DNA across multiple Pneumocystis species suggest a vertical transmission at least 100 million years ago. Common ancestry of Pneumocystis and S. pombe centromeres is untraceable at the DNA level but the overall architectural similarity could be the result of functional constraint for successful chromosomal segregation. Significance StatementPneumocystis species offer a suitable genetic system to study centromere evolution in pathogens because of their phylogenetic proximity with the nonpathogenic yeast Schizosaccharomyces pombe, a popular model for cell biology. We used this system to explore how centromeres have evolved after divergence of the two clades [~]460 million years ago. To address this question, we established a protocol combining short-term culture and ChIP-Seq to characterize centromeres in multiple Pneumocystis species. We show that Pneumocystis have short epigenetic centromeres that function differently from those in S. pombe. One sentence summaryInsights into the formation of genic centromeres in fungal pathogens.

genomics↗

bioRxiv2022

A quantitative and spatial analysis of cell cycle regulators during the fission yeast cell cycle

We have carried out a systems-level analysis of the spatial and temporal dynamics of cell cycle regulators in the fission yeast Schizosaccharomyces pombe. In a comprehensive single cell analysis we have precisely quantified the levels of 38 proteins previously identified as regulators of the G2 to mitosis transition, and of 7 proteins acting at the G1 to S-phase transition. Only two of the 38 mitotic regulators exhibit changes in concentration at the whole cell level, the mitotic B-type cyclin Cdc13 which accumulates continually throughout the cell cycle, and the regulatory phosphatase Cdc25 which exhibits a complex cell cycle pattern. Both proteins show similar patterns of change within the nucleus as in the whole cell but at higher concentrations. In addition, the concentrations of the major fission yeast cyclin dependent kinase (CDK) Cdc2, the CDK regulator Suc1 and the inhibitory kinase Wee1 also increase in the nucleus peaking at mitotic onset but are constant in the whole cell. The significant increase in concentration with size for Cdc13 supports the model that mitotic B-type cyclin accumulation acts as a cell size sensor. We propose a two-step process for the control of mitosis. First, Cdc13 accumulates in a size-dependent manner which drives increasing CDK activity. Second, from mid G2 the increasing nuclear accumulation of Cdc25 and the counteracting Wee1 introduces a bistability switch that results in a rapid rise of CDK activity at the end of G2 and thus brings about an orderly progression into mitosis. Significance StatementAcross eukaryotes the increasing level of cyclin dependent kinase (CDK) activity drives progression through the cell cycle. As most cells divide at specific sizes, information responding to the size of the cell must feed into the regulation of CDK activity. In this study, we use fission yeast to precisely measure how proteins that have been previously identified in genome wide screens as cell cycle regulators change in their levels with cell cycle progression. We identify the mitotic B-type cyclin Cdc13 and mitotic inhibitory phosphatase Cdc25 as the only two proteins that change in both whole cell and nuclear concentration through the cell cycle, making them candidates for universal cell size sensors at the onset of mitosis and cell division.

cell biology↗