The budding yeast nuclear envelope adjacent to the nucleolus serves as a membrane sink during mitotic delay.
The mechanisms that dictate nuclear shape are largely unknown. Here we screened the budding yeast deletion collection for mutants with abnormal nuclear shape. A common phenotype was the appearance of a nuclear extension, particularly in mutants in DNA repair and chromosome segregation genes. Our data suggest that these mutations led to the abnormal nuclear morphology indirectly, by causing a checkpoint-induced cell-cycle delay. Indeed, delaying cells in mitosis by other means also led to the appearance of nuclear extensions, whereas inactivating the DNA damage checkpoint pathway in a DNA repair mutant reduced the fraction of cells with nuclear extensions. Formation of a nuclear extension was specific to a mitotic delay, because cells arrested in S or G2 had round nuclei. Moreover, the nuclear extension always coincided with the nucleolus, while the morphology of the DNA mass remained largely unchanged. Finally, we found that phospholipid synthesis continued unperturbed when cells delayed in mitosis, and inhibiting phospholipid synthesis abolished the formation of nuclear extensions. Our data suggest a mechanism that promotes nuclear envelope expansion during mitosis. When mitotic progression is delayed, cells sequester the added membrane to the nuclear envelope associated with the nucleolus, possibly to avoid disruption of intranuclear organization.
Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Keren L
KL
Witkin
Yolanda
Y
Chong
Sichen
S
Shao
Micah T
MT
Webster
Sujoy
S
Lahiri
Alison D
AD
Walters
Brandon
B
Lee
Judice L Y
JL
Koh
William A
WA
Prinz
Brenda J
BJ
Andrews
Orna
O
Cohen-Fix
D002466:Cell Nucleolus / Q000378:metabolism; D002467:Cell Nucleus / Q000502:physiology*; D020090:Chromosome Segregation / Q000235:genetics; D004252:DNA Mutational Analysis; D004260:DNA Repair / Q000235:genetics; D017353:Gene Deletion; D008856:Microscopy, Fluorescence; D008938:Mitosis / Q000235:genetics / Q000502:physiology*; D009685:Nuclear Envelope / Q000378:metabolism*; D053140:Organelle Shape / Q000502:physiology*; D010743:Phospholipids / Q000096:biosynthesis; D004718:Saccharomycetales / Q000235:genetics / Q000502:physiology*
D010743:Phospholipids