Biology subjects

Cooper, J. P.

Publications and source records attributed to Cooper, J. P..

5 recordsLinked to original sources

bioRxiv2026

Telomeric heterochromatin acts in trans to promote meiotic centromere assembly via Aurora B kinase recruitment

During meiosis, chromosomes face a paradox: the machinery that ensures reductional chromosome segregation also destabilizes centromeres by dismantling kinetochores, risking chromosome missegregation. Here we show how cells resolve this crisis through an unexpected activity of the telomere bouquet. We demonstrate that the bouquet transfers heterochromatin components to pericentromeres, which in turn recruit the Aurora B kinase to direct centromere reassembly. The heterochromatin protein Swi6HP1 relocates from telomeres to centromeres, enabling Haspin kinase-dependent phosphorylation of histone H3 and consequent enrichment of the chromosomal passenger complex, which includes the Aurora B kinase. Aurora B then phosphorylates core centromere proteins, including CenpA and CenpC, to promote kinetochore reassembly. Phosphomimetic mutants of CenpA or CenpC bypass the telomere-heterochromatin-Haspin pathway, demonstrating that Aurora B-mediated phosphorylation is sufficient for reassembly. This function is conserved in mitotically proliferating cells subjected to centromere dismantlement. Our findings establish a safeguarded system that couples meiotic nuclear architecture to centromere identity and reveal a fundamental role for the Aurora B kinase in centromere assembly, beyond its canonical function in correcting kinetochore-spindle attachment errors.

cell biology↗

bioRxiv2023

Parallel genetic screens identify nuclear envelope homeostasis as a key determinant of telomere entanglement resolution in fission yeast

In fission yeast lacking the telomere binding protein, Taz1, replication stalls at telomeres, triggering deleterious downstream events. Strand invasion from one taz1{Delta} telomeric stalled fork to another on a separate (non-sister) chromosome leads to telomere entanglements, which are resolved in mitosis at 32{degrees}C; however, entanglement resolution fails at [≤]20{degrees}C, leading to cold-specific cell lethality. Previously, we found that loss of the mitotic function of Rif1, a conserved DNA replication and repair factor, suppresses cold sensitivity by promoting resolution of entanglements without affecting entanglement formation. To understand the underlying pathways of mitotic entanglement resolution, we performed a series of genomewide synthetic genetic array screens to generate a comprehensive list of genetic interactors of taz1{Delta} and rif1{Delta}. We modified a previously described screening method to ensure that the queried cells were kept in log phase growth. In addition to recapitulating previously identified genetic interactions, we find that loss of genes encoding components of nuclear pore complexes (NPCs) promotes telomere disentanglement and suppresses taz1{Delta} cold sensitivity; we attribute this to more rapid anaphase midregion nuclear envelope (NE) breakdown in the absence of these NPC components. Moreover, loss of genes involved in lipid metabolism reverses the ability of rif1+ deletion to suppress taz1{Delta} cold sensitivity, again pinpointing NE modulation. A rif1+ separation-of-function mutant that specifically loses Rif1s mitotic functions yields similar genetic interactions. Genes promoting membrane fluidity were enriched in a parallel taz1+ synthetic lethal screen at permissive temperature, cementing the idea that the cold specificity of taz1{Delta} lethality stems from altered NE homeostasis.

genetics↗

bioRxiv2023

Fate of telomere entanglements is dictated by the timing of anaphase midregion nuclear envelope breakdown

Persisting replication intermediates can confer mitotic catastrophe if left unresolved. Loss of the fission yeast telomere protein Taz1 (ortholog of mammalian TRF1/TRF2) causes telomeric replication fork stalling and in turn, telomere entanglements that stretch between the segregating chromosomes at anaphase. At [≤]20{degrees}C, these entanglements fail to resolve, resulting in lethality. Rif1, a conserved DNA replication/repair protein, localizes between the segregating chromosomes and specifically hinders the resolution of telomere entanglements without affecting their formation. During anaphase, the spindle and the last segments of segregating chromatin are encased by the nuclear envelope (NE), creating a microdomain termed the anaphase midregion. In the final stages of fission yeast mitosis, this midregion undergoes local NE breakdown. Here we demonstrate that in response to taz1{Delta} telomeric entanglements, Rif1 delays midregion NE breakdown, and this delay disfavors entanglement resolution. Accordingly, gene deletions that hasten midregion NE breakdown phenocopy, and are epistatic with, rif1+ deletion. Conversely, gene deletions that delay midregion NE breakdown block the taz1{Delta} telomere detanglement afforded by loss of Rif1. Overexpression of Rif1 in a wild type background causes cold-specific NE defects and lethality, which are rescued by treatment with a membrane fluidizing agent. We propose that delayed NE breakdown normally favors the resolution of simple entanglements, arising from incomplete replication, by delaying exposure to the cytoplasm. In contrast, resolution of more complex entanglements involving strand invasion, like entanglements between nonsister taz1{Delta} telomeres, requires more rapid exposure to the cytoplasm. These observations uncover an unexpected coordination between NE remodeling and DNA processing events that can prevent or promote aneuploidy.

molecular biology↗

bioRxiv2021

RNAi and Ino80 complex control rate limiting translocation step that moves rDNA to eroding telomeres

The discovery of HAATIrDNA, a mode of telomerase-negative survival in which canonical telomeres are replaced with ribosomal DNA (rDNA) repeats that acquire chromosome end-protection capability, raised crucial questions as to how rDNA tracts jump to eroding, nonhomologous chromosome ends. Here we show that HAATIrDNA formation is initiated and limited by a single translocation that juxtaposes rDNA from Chromosome (Chr) III onto subtelomeric elements (STE) on Chr I or II; this rare reaction requires the RNAi pathway and the Ino80 nucleosome remodeling complex (Ino80C), thus defining an unforeseen relationship between these two machineries. The unique STE-rDNA junction created by this initial translocation is efficiently copied to the remaining STE chromosome ends, without the need for RNAi or Ino80C, forming HAATIrDNA. Intriguingly, both the RNAi and Ino80C machineries contain a component that plays dual roles in HAATI subtype choice. Dcr1 of the RNAi pathway and Iec1 of the Ino80C both promote HAATIrDNA formation as part of their respective canonical machineries, but both also inhibit formation of the exceedingly rare HAATISTE (in which STE sequences mobilize throughout the genome and assume chromosome end protection capacity) in non-canonical, pathway-independent manners. This work provides a glimpse into a previously unrecognized crosstalk between RNAi and Ino80C in controlling unusual translocation reactions that establish telomere-free linear chromosome ends.

molecular biology↗

bioRxiv2017

Distinct ‘safe zones’ at the nuclear envelope ensure robust replication of heterochromatic chromosome regions

Chromosome replication and transcription occur within a complex nuclear milieu whose functional subdomains are beginning to be mapped out. Here we delineate distinct domains of the fission yeast nuclear envelope (NE), focusing on regions enriched for the inner NE protein, Bqt4, or the lamin interacting domain protein, Lem2. Bqt4 is relatively mobile around the NE and acts in two capacities. First, Bqt4 tethers chromosome termini and the mat locus to the NE specifically while these regions are replicating. This positioning is required for robust chromatin replication. Second, Bqt4 mobilizes a subset of Lem2 molecules around the NE to promote pericentric heterochromatin maintenance. Opposing Bqt4-dependent Lem2 mobility are factors that stabilize Lem2 beneath the centrosome, where Lem2 plays a crucial role in kinetochore maintenance. Our data prompt a model in which Bqt4-rich nuclear subdomains are safe zones in which collisions between transcription and replication are averted and heterochromatin is reassembled faithfully.

genetics↗