Abstract:The architecture and nuclear location of chromosomes affect chromatin events. Rif1, a crucial regulator of replication timing, recognizes G-quadruplex and inhibits origin firing over the 50–100-kb segment in fission yeast,Schizosaccharomyces pombe, leading us to postulate that Rif1 may generate chromatin higher order structures inhibitory for initiation. However, the effects of Rif1 on chromatin localization in nuclei have not been known. We show here that Rif1 overexpression causes growth inhibition and event… Show more
“…This contrasts with the hypersensitivity of Rif1-overexpressing cells to hydroxyurea treatment, which is shared with the S-rif1+ allele (Figure S3B) and likely stems from exaggerating the inhibitory function of Rif1 in restraining early origin activation, resulting in genomic under-replication. Our observations are consistent with a recent report that ectopic overexpression of Rif1 from a high copy number plasmid is toxic for S. pombe cells 45 .…”
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°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 totaz1Δtelomeric 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 thetaz1Δtelomere 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 nonsistertaz1Δtelomeres, 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.
“…This contrasts with the hypersensitivity of Rif1-overexpressing cells to hydroxyurea treatment, which is shared with the S-rif1+ allele (Figure S3B) and likely stems from exaggerating the inhibitory function of Rif1 in restraining early origin activation, resulting in genomic under-replication. Our observations are consistent with a recent report that ectopic overexpression of Rif1 from a high copy number plasmid is toxic for S. pombe cells 45 .…”
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°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 totaz1Δtelomeric 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 thetaz1Δtelomere 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 nonsistertaz1Δtelomeres, 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.
“…S5c ) and likely stems from exaggerating the inhibitory function of Rif1 in restraining early origin activation, resulting in genomic under-replication. Our observations are consistent with a recent report that shows ectopic overexpression of Rif1 from a high copy number plasmid is toxic for S. pombe cells 46 . Fig.…”
Persisting replication intermediates can confer mitotic catastrophe. Loss of the fission yeast telomere protein Taz1 (ortholog of mammalian TRF1/TRF2) causes telomeric replication fork (RF) stalling and consequently, telomere entanglements that stretch between segregating mitotic chromosomes. At ≤20 °C, these entanglements fail to resolve, resulting in lethality. Rif1, a conserved DNA replication/repair protein, hinders the resolution of telomere entanglements without affecting their formation. At mitosis, local nuclear envelope (NE) breakdown occurs in the cell’s midregion. Here we demonstrate that entanglement resolution occurs in the cytoplasm following this NE breakdown. However, in response to taz1Δ telomeric entanglements, Rif1 delays midregion NE breakdown at ≤20 °C, in turn disfavoring entanglement resolution. Moreover, Rif1 overexpression in an otherwise wild-type setting causes cold-specific NE defects and lethality, which are rescued by membrane fluidization. Hence, NE properties confer the cold-specificity of taz1Δ lethality, which stems from postponement of NE breakdown. We propose that such postponement promotes clearance of simple stalled RFs, but resolution of complex entanglements (involving strand invasion between nonsister telomeres) requires rapid exposure to the cytoplasm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
