Biology subjects

Tsang, M. J.

Publications and source records attributed to Tsang, M. J..

3 recordsLinked to original sources

bioRxiv2025

Differential roles for the spindle assembly checkpoint in error surveillance and mitotic timing

The Spindle Assembly Checkpoint (SAC) plays critical roles in regulating mitotic fidelity and progression. Here, we utilized a SAC-deficient cell line lacking the full-length Cdc20 translational protein isoform (Cdc20 {Delta}FL) to define its differential genetic interactions using CRISPR/Cas9-based gene targeting. Cdc20 {Delta}FL cells display synthetic lethal relationships with gene targets required for proper chromosome segregation, highlighting the critical role of the SAC in error surveillance. Surprisingly, we found that the checkpoint component Mad2 becomes dispensable for viability in Cdc20 {Delta}FL cells. Prior work suggested that Mad2 acts as an essential mitotic "timer" to control mitotic duration in unperturbed cells. Instead, our functional analysis indicates that the mitotic timer depends on the interdependent and overlapping actions of: (1) Mad2 inhibition of APC/C-Cdc20, (2) Cdk1-mediated phosphorylation of Cdc20, and (3) total Cdc20 protein levels. Simultaneously perturbing these pathways results in near immediate mitotic exit and catastrophic chromosome mis-segregation.

cell biology↗

bioRxiv2023

Spatial transcriptome profiling uncovers metabolic regulation of left-right patterning

Left-right patterning disturbance can cause severe birth defects, but it remains least understood of the three body axes. We uncovered an unexpected role for metabolic regulation in left-right patterning. Analysis of the first spatial transcriptome profile of left-right patterning revealed global activation of glycolysis, accompanied by right-sided expression of Bmp7 and genes regulating insulin growth factor signaling. Cardiomyocyte differentiation was left-biased, which may underlie the specification of heart looping orientation. This is consistent with known Bmp7 stimulation of glycolysis and glycolysis suppression of cardiomyocyte differentiation. Liver/lung laterality may be specified via similar metabolic regulation of endoderm differentiation. Myo1d, found to be left-sided, was shown to regulate gut looping in mice, zebrafish, and human. Together these findings indicate metabolic regulation of left-right patterning. This could underlie high incidence of heterotaxy-related birth defects in maternal diabetes, and the association of PFKP, allosteric enzyme regulating glycolysis, with heterotaxy. This transcriptome dataset will be invaluable for interrogating birth defects involving laterality disturbance.

developmental biology↗

bioRxiv2021

Alternative Cdc20 translational isoforms bypass the spindle assembly checkpoint to control mitotic arrest duration

Mitotic chromosome segregation defects activate the Spindle Assembly Checkpoint (SAC), which inhibits the APC/C co-activator Cdc20 to induce a prolonged cell cycle arrest. Once errors are corrected, the SAC is silenced thereby allowing anaphase onset and mitotic exit to proceed. However, in the presence of persistent, unresolvable errors, cells can undergo "mitotic slippage", exiting mitosis into a tetraploid G1 state and escaping the cell death that results from a prolonged arrest. The molecular logic that allows cells to balance these dueling mitotic arrest and slippage behaviors remains unclear. Here we demonstrate that human cells modulate their mitotic arrest duration through the presence of conserved, alternative Cdc20 translational isoforms. Translation initiation at downstream start sites results in truncated Cdc20 isoforms that are resistant to SAC-mediated inhibition and promote mitotic exit even in the presence of mitotic perturbations. Targeted molecular changes or naturally-occurring mutations in cancer cells that alter the relative Cdc20 isoform levels or its translational regulatory control modulate both mitotic arrest duration and anti-mitotic drug sensitivity. Our work reveals a critical role for the differential translational regulation of Cdc20 in mitotic arrest timing, with important implications for the diagnosis and treatment of human cancers.

cell biology↗