Biology subjects

Sunkel, C. E.

Publications and source records attributed to Sunkel, C. E..

4 recordsLinked to original sources

bioRxiv2024

POLO kinase inhibits Protein Phosphatase 1 to promote the Spindle Assembly Checkpoint and prevent aneuploidy

Protein phosphatase 1 (PP1) is essential for spindle assembly checkpoint (SAC) silencing and mitotic exit, but its regulation during mitosis remains ill-defined. Here, we demonstrate in vitro and in Drosophila cells that the mitotic kinase POLO phosphorylates PP187B at a conserved residue (T286) within a pocket implicated in the recognition of RVxF-containing target proteins. Phosphorylation of T286 inhibits PP187B binding to the RVxF motif of the SAC kinase MPS1, dampening the dephosphorylation of MPS1 T-loop. Phosphorylation of T286 is dynamically regulated during mitosis. It occurs at unattached/tensionless kinetochores and decreases as chromosomes congress. Expression of phosphomimetic PP187BT286D prevents MPS1 inactivation in metaphase and causes a SAC-dependent delay of anaphase onset. Conversely, an unphosphorylatable PP187BT286A mutant impairs MPS1 activation at unattached kinetochores and weakens the SAC. In vivo, larval neuroblasts expressing PP187BT286 phosphomutants exhibit frequent chromosome mis-segregation and aneuploidy. Thus, our findings identify POLO-mediated phosphorylation of PP187B as a critical regulatory strategy that fine-tunes phosphatase activity to ensure a robust and timely SAC and prevent genome instability.

cell biology↗

bioRxiv2024

Proximity-based activation of AURORA A by MPS1 potentiates error correction

Faithfull cell division relies on mitotic chromosomes becoming bioriented with each pair of sister kinetochores bound to microtubules oriented toward opposing spindle poles. Erroneous kinetochore-microtubule attachments often form during early mitosis, but are destabilized through the phosphorylation of outer kinetochore proteins by centromeric AURORA B kinase (ABK) and centrosomal AURORA A kinase (AAK), thus allowing for re-establishment of attachments until biorientation is achieved. MPS1-mediated phosphorylation of NDC80 has also been shown to directly weaken the kinetochore-microtubule interface in yeast. In human cells, MPS1 has been proposed to transiently accumulate at end-on attached kinetochores and phosphorylate SKA3 to promote microtubule release. Whether MPS1 directly targets NDC80 and/or promotes the activity of AURORA kinases in metazoans remains unclear. Here, we report a novel mechanism involving communication between kinetochores and centrosomes, wherein MPS1 acts upstream of AAK to promote error correction. MPS1 on pole-proximal kinetochores phosphorylates the C-lobe of AAK thereby increasing its activation at centrosomes. This proximity-based activation ensures the establishment of a robust AAK activity gradient that locally destabilizes mal-oriented kinetochores near spindle poles. Accordingly, MPS1 depletion from Drosophila cells causes severe chromosome misalignment and erroneous kinetochore-microtubule attachments, which can be rescued by tethering either MPS1 or constitutively active AAK mutants to centrosomes. Proximity-based activation of AAK by MPS1 also occurs in human cells to promote AAK-mediated phosphorylation of the NDC80 N-terminal tail. These findings uncover an MPS1-AAK cross-talk that is required for efficient error correction, showcasing the ability of kinetochores to modulate centrosome outputs to ensure proper chromosome segregation.

cell biology↗

bioRxiv2022

Apical constriction induces tissue rupture in a proliferative epithelium

Apical-basal polarity is an essential epithelial trait controlled by the evolutionarily conserved PAR-aPKC polarity network. Deregulation of polarity proteins disrupts tissue organization during development and in disease, but the underlying mechanisms are unclear due to the broad implications of polarity loss. Here, we uncovered how Drosophila aPKC maintains epithelial architecture by directly observing tissue disorganization after fast optogenetic inactivation in living adult flies and ovaries cultured ex vivo. We show that fast aPKC perturbation in the proliferative follicular epithelium produces large epithelial gaps that result from increased apical constriction, rather than loss of apical-basal polarity. Accordingly, we could modulate the incidence of epithelial gaps by increasing and decreasing actomyosin-driven contractility. We traced the origin of epithelial gaps to tissue rupture next to dividing cells. Live imaging shows that aPKC perturbation rapidly induces apical constriction in non-mitotic cells, producing pulling forces that ultimately detach dividing and neighbouring cells. We further demonstrate that epithelial rupture requires a global increase of apical constriction, since it was prevented by the presence of non-constricting cells. Conversely, a global induction of apical tension through light-induced recruitment of RhoGEF2 to the apical side was sufficient to produce tissue rupture. Hence, our work reveals that the roles of aPKC in polarity and actomyosin regulation are separable and provides the first in vivo evidence that excessive tissue stress can break the epithelial barrier during proliferation.

developmental biology↗

bioRxiv2018

Aneuploidy Promotes Intestinal Dysplasia in Drosophila

Aneuploidy is associated with different human diseases, particularly cancer, but how different cell types within tissues respond to aneuploidy is not fully understood. In some studies, aneuploidy has been shown to have a deleterious effect and lead to cell death, however it has also been shown to be a causal event of tumorigenesis in other contexts.\n\nHere, we show that Drosophila intestinal stem cells have a particular tolerance to aneuploidy and do not activate apoptosis in response to chromosome misegregation like other non-stem cells. Instead, we observe the development of tissue dysplasia characterized by an accumulation of progenitor cells, increased stem cell proliferation rate, and an excess of cells of the enteroendocrine lineage. Our findings highlight the importance of mechanisms acting to prevent aneuploidy within tissue stem cells and provide an in vivo model of how these cells can act as reservoirs for genomic alterations that can lead to dysplasia.

developmental biology↗