Biology subjects

Budrewicz, J.

Publications and source records attributed to Budrewicz, J..

3 recordsLinked to original sources

bioRxiv2023

Cyclin B3 is a dominant fast-acting cyclin that drives rapid early embryonic mitoses

In many species, early embryonic mitoses proceed at a very rapid pace, but how this pace is achieved is not understood. Here we show that in the early C. elegans embryo, cyclin B3 is the dominant driver of rapid embryonic mitoses. Metazoans typically have three cyclin B isoforms that associate with and activate Cdk1 kinase to orchestrate mitotic events: the related cyclins B1 and B2 and the more divergent cyclin B3. We show that whereas embryos expressing cyclins B1 and B2 support slow mitosis (NEBD to Anaphase [~] 600s), the presence of cyclin B3 dominantly drives the [~]3-fold faster mitosis observed in wildtype embryos. CYB-1/2-driven mitosis is longer than CYB-3-driven mitosis primarily because the progression of mitotic events itself is slower, rather than delayed anaphase onset due to activation of the spindle checkpoint or inhibitory phosphorylation of the anaphase activator CDC-20. Addition of cyclin B1 to cyclin B3-only mitosis introduces an [~]60s delay between the completion of chromosome alignment and anaphase onset, which likely ensures segregation fidelity; this delay is mediated by inhibitory phosphorylation on CDC-20. Thus, the dominance of cyclin B3 in driving mitotic events, coupled to introduction of a short cyclin B1-dependent delay in anaphase onset, sets the rapid pace and ensures fidelity of mitoses in the early C. elegans embryo.

cell biology↗

bioRxiv2022

Nuclear-enriched protein phosphatase 4 ensures outer kinetochore assemblyprior to nuclear dissolution

A landmark event in the transition from interphase to mitosis in metazoans is nuclear envelope breakdown (NEBD). Many events important for mitosis occur prior to NEBD, including condensation of replicated chromosomes and assembly of kinetochores to rapidly engage spindle microtubules. Here we show that nuclear-enriched protein phosphatase 4 (PP4) ensures robust assembly of the microtubule-coupling outer kinetochore prior to NEBD. In the absence of PP4, chromosomes exhibit extended monopolar orientation after NEBD and subsequently mis-segregate. A secondary consequence of diminished outer kinetochore assembly is defective sister chromatid resolution. After NEBD, a cytoplasmic activity compensates for PP4 loss, leading to outer kinetochore assembly and recovery of chromosomes from monopolar orientation to significant biorientation. The Ndc80-Ska microtubule-binding module of the outer kinetochore is required for this recovery. PP4 associates with the inner kinetochore protein CENP-C; however, disrupting the PP4-CENP-C interaction does not perturb chromosome segregation. These results establish that PP4-dependent outer kinetochore assembly prior to NEBD is critical for timely and proper engagement of chromosomes with spindle microtubules.

cell biology↗

bioRxiv2020

PP2A:B56 Regulates Meiotic Chromosome Segregation in C. elegans Oocytes

Protein Phosphatase 2A (PP2A) is an heterotrimer composed of scaffolding (A), catalytic (C), and regulatory (B) subunits with various key roles during cell division. While A and C subunits form the core enzyme, the diversity generated by interchangeable B subunits dictates substrate specificity. Within the B subunits, B56-type subunits play important roles during meiosis in yeast and mice by protecting centromeric cohesion and stabilising the kinetochore-microtubule attachments. These functions are achieved through targeting of B56 subunits to centromere and kinetochore by Shugoshin and BUBR1. In the nematode Caenorhabditis elegans (C. elegans) the closest BUBR1 ortholog lacks the B56 interaction domain and the Shugoshin orthologue is not required for normal segregation during oocyte meiosis. Therefore, the role of PP2A in C. elegans female meiosis is not known. Here, we report that PP2A is essential for meiotic spindle assembly and chromosome dynamics during C. elegans female meiosis. Specifically, B56 subunits PPTR-1 and PPTR-2 associate with chromosomes during prometaphase I and regulate chromosome congression. The chromosome localization of B56 subunits does not require shugoshin orthologue SGO-1. Instead we have identified the kinase BUB-1 as the key B56 targeting factor to the chromosomes during meiosis. PP2A BUB-1 recruits PP2A:B56 to the chromosomes via dual mechanism: 1) PPTR-1/2 interacts with the newly identified LxxIxE short linear motif (SLiM) within a disordered region in BUB-1 in a phosphorylation-dependent manner; and 2) PPTR-2 can also be recruited to chromosomes in a BUB-1 kinase domain-dependent manner. Our results highlight a novel, BUB-1-dependent mechanism for B56 recruitment, essential for recruiting a pool of PP2A required for proper chromosome congression during meiosis I.

cell biology↗