Biology subjects

Allan, L. A.

Publications and source records attributed to Allan, L. A..

4 recordsLinked to original sources

bioRxiv2025

The mitotic stopwatch limits the proliferation of whole genome doubled cells

AO_SCPLOWBSTRACTC_SCPLOWWhole genome doubling (WGD) is a frequent event in tumourigenesis that promotes chromosomal instability and tumour evolution. WGD is sensed indirectly due to the presence of extra centrosomes, which activate the PIDDosome to induce a p53-dependent G1-arrest. Here we uncouple WGD from centrosome amplification and show that p53 still arrests tetraploid cells, but via the mitotic stopwatch; a p53/53BP1/USP28-dependent pathway that causes G1-arrest following an extended mitotic delay. Mitotic timing is unaffected by WGD, but the threshold mitotic delay needed to invoke a G1-arrest is reduced. This sensitivity to the stopwatch mechanism is not associated with altered levels of mitotic stopwatch components, but instead, is associated with enhanced p21 concentrations prior to mitosis. Similar effects are observed in diploid cells treated with CDK4/6 inhibitors to double their size, implicating G1 delays and cell size as key determinants of stopwatch sensitivity. This ability of the mitotic stopwatch to arrest proliferation after increases to genome or cell size has important implications for the progression and treatment of cancer. It also demonstrates that the stopwatch pathway can sense more than just mitotic delays.

cell biology↗

bioRxiv2022

A bifunctional kinase-phosphatase module integrates mitotic checkpoint and error-correction signalling to ensure mitotic fidelity

Two major mechanisms have evolved to safeguard genome stability during mitosis: the mitotic checkpoint delays mitosis until all chromosomes have attached to microtubules, and the kinetochore-microtubule error-correction pathway keeps this attachment process free from errors. We demonstrate here that the optimal strength and dynamics of both processes is set by a kinase-phosphatase pair (PLK1-PP2A) that engage in negative feedback on the BUB complex. Uncoupling this homeostatic feedback to skew the balance towards PLK1 produces a strong checkpoint, weak microtubule attachments, and mitotic delays. Conversely, skewing the balance towards PP2A causes a weak checkpoint, strong microtubule attachments, and chromosome segregation errors. The number of MELT motifs on the KNL1 signalling scaffold sets the optimal levels of each enzyme, because engineering KNL1 to recruit too many BUB complexes increases KNL1-PLK1/PP2A levels, and enhances checkpoint/microtubule attachment strength. In contrast, recruiting too few BUB complexes lowers KNL1-PLK1/PP2A, and decreases checkpoint/microtubule attachment strength. Both of these situations are associated with chromosome segregation errors. Together, these data demonstrate how a single bifunctional kinase-phosphatase module integrates two major mitotic processes to help preserve genome stability.

cell biology↗

bioRxiv2019

Cyclin B1 scaffolds MAD1 at the corona to activate the spindle assembly checkpoint

The Cyclin B:CDK1 kinase complex is the master regulator of mitosis that phosphorylates hundreds of proteins to coordinate mitotic progression. We show here that, in addition to these kinase functions, Cyclin B also scaffolds a localised signalling pathway to help preserve genome stability. Cyclin B1 localises to an expanded region of the outer kinetochore, known as the corona, where it scaffolds the spindle assembly checkpoint (SAC) machinery by binding directly to MAD1. In vitro reconstitutions map the key binding interface to a few acidic residues in the N-terminus of MAD1, and point mutations in this region remove corona MAD1 and weaken the SAC. Therefore, Cyclin B1 is the long-sought-after scaffold that links MAD1 to the corona and this specific pool of MAD1 is needed to generate a robust SAC response. Robustness, in this context, arises because Cyclin B1-MAD1 localisation becomes MPS1-independent after the corona has been established. We demonstrate that this allows corona-MAD1 to persist at kinetochores when MPS1 activity falls, ensuring that it can still be phosphorylated on a key C-terminal catalytic site by MPS1. Therefore, this study explains how corona MAD1 generates a robust SAC signal and why stripping of this pool by dynein is essential for SAC silencing. It also reveals that the key mitotic kinase, Cyclin B1-Cdk1, scaffolds the pathway that inhibits its own degradation.

cell biology↗

bioRxiv2018

A molecular explanation for PP2A-B56 isoform specificity during mitosis

PP2A-B56 is a serine/threonine phosphatase complex that regulates several major mitotic processes, including sister chromatid cohesion, kinetochore-microtubule attachment and the spindle assembly checkpoint. We show here that these key functions are shared between B56 isoforms which localise differentially to either the centromere or kinetochore. The centromeric B56 isoforms rely on a specific interaction with Sgo2, whereas the kinetochore isoforms bind preferentially to BubR1 and other proteins containing an LxxIxE motif. The molecular basis for this differential localisation can be mapped to a small C-terminal region in B56 that regulates these key interactions and defines whether PP2A-B56 complexes bind to either the centromere or kinetochore. Together, this study describes how different PP2A-B56 complexes utilise isoform-specific interactions to control distinct processes during mitosis.

cell biology↗