Gerhold AR et al. (2015) Curr Biol "Investigating the regulation of stem and progenitor cell mitotic progression by in situ imaging."

Maddox PS, Gerhold AR, Dorn JF, Vallee-Trudeau JN, Ryan J, Labbe JC

[Curr Biol, 2015]

Genome stability relies upon efficacious chromosome congression and regulation by the spindle assembly checkpoint (SAC). The study of these fundamental mitotic processes in adult stem and progenitor cells has been limited by the technical challenge of imaging mitosis in these cells in situ. Notably, how broader physiological changes, such as dietary intake or age, affect mitotic progression in stem and/or progenitor cells is largely unknown. Using in situ imaging of C. elegans adult germlines, we describe the mitotic parameters of an adult stem and progenitor cell population in an intact animal. We find that SAC regulation in germline stem and progenitor cells is distinct from that found in early embryonic divisions and is more similar to that of classical tissue culture models. We further show that changes in organismal physiology affect mitotic progression in germline stem and progenitor cells. Reducing dietary intake produces a checkpoint-dependent delay in anaphase onset, and inducing dietary restriction when the checkpoint is impaired increases the incidence of segregation errors in mitotic and meiotic cells. Similarly, developmental aging of the germline stem and progenitor cell population correlates with a decline in the rate of several mitotic processes. These results provide the first in vivo validation of models for SAC regulation developed in tissue culture systems and demonstrate that several fundamental features of mitotic progression in adult stem and progenitor cells are highly sensitive to organismal physiological changes.

Gerhold AR et al. (2018) Mol Biol Cell "Spindle assembly checkpoint strength is linked to cell fate in the C. elegans embryo."

Poupart V, Maddox PS, Labbe JC, Gerhold AR

[Mol Biol Cell, 2018]

The spindle assembly checkpoint (SAC) is a conserved mitotic regulator that preserves genome stability by monitoring kinetochore-microtubule attachments and blocking anaphase onset until chromosome bi-orientation is achieved. Despite its central role in maintaining mitotic fidelity, the ability of the SAC to delay mitotic exit in the presence of kinetochore-microtubule attachment defects (SAC "strength") appears to vary widely. How different cellular aspects drive this variation remains largely unknown. Here we show that SAC strength is correlated with cell fate during development of C. elegans embryos, with germline-fated cells experiencing longer mitotic delays upon spindle perturbation than somatic cells. These differences are entirely dependent on an intact checkpoint and only partially attributable to differences in cell size. In 2-cell embryos, cell size accounts for half of the difference in SAC strength between the larger somatic AB and the smaller germline P₁ blastomeres. The remaining difference requires asymmetric cytoplasmic partitioning downstream of PAR polarity proteins, suggesting that checkpoint regulating factors are distributed asymmetrically during early germ cell divisions. Our results indicate that SAC activity is linked to cell fate and reveal a hitherto unknown interaction between asymmetric cell division and the SAC. Movie S1 Movie S1 zyg-1(ts)-induced monopolar spindles in 2- and 4-cell stage embryos. Movie S2 Movie S2 tbb-2(ts)-induced spindle defects in 2- and 4-cell stage embryos. Movie S3 Movie S3 A P₂ cell from a permeabilized embryo treated with DMSO. Movie S4 Movie S4 A P₂ cell from a permeabilized embryo treated with 33M Nocodazole. Movie S5 Movie S5 zyg-1(ts)-induced monopolar spindles in 2- and 4-cell stage embryos following RNAi depletion of MDF-1.