Inner nuclear membrane protein Lem2 augments heterochromatin formation in response to nutritional conditions

Abstract

Inner nuclear membrane proteins interact with chromosomes in the nucleus and are important for chromosome activity. Lem2 and Man1 are conserved members of the LEM-domain nuclear membrane protein family. Mutations of LEM-domain proteins are associated with laminopathy, but their cellular functions remain unclear. Here, we report that Lem2 maintains genome stability in the fission yeast Schizosaccharomyces pombe. S. pombe cells disrupted for the lem2 + gene (lem2Δ) showed slow growth and increased rate of the minichromosome loss. These phenotypes were prominent in the rich culture medium, but not in the minimum medium. Centromeric heterochromatin formation was augmented upon transfer to the rich medium in wild-type cells. This augmentation of heterochromatin formation was impaired in lem2Δ cells. Notably, lem2Δ cells occasionally exhibited spontaneous duplication of genome sequences flanked by the long-terminal repeats of retrotransposons. The resulting duplication of the lnp1 + gene, which encodes an endoplasmic reticulum membrane protein, suppressed lem2Δ phenotypes, whereas the lem2Δ lnp1Δ double mutant showed a severe growth defect. A combination of mutations in Lem2 and Bqt4, which encodes a nuclear membrane protein that anchors telomeres to the nuclear membrane, caused synthetic lethality. These genetic interactions imply that Lem2 cooperates with the nuclear membrane protein network to regulate genome stability.

LEM2 recruits CHMP7 for ESCRT-mediated nuclear envelope closure in fission yeast and human cells

“…This conserved pathway may likewise underlie the requirement for Src1, a LEM-domain protein in Aspergillus nidulans , in the formation of stable nuclei (37). This body of work suggests that LEM2 plays a specific, initiating role in coordinating membrane remodeling events, particularly during nuclear assembly, in addition to the other roles it plays as a NE resident during interphase (31, 35, 38–43). …”

An unconventional interaction between Dis1/TOG and Mal3/EB1 in fission yeast promotes the fidelity of chromosome segregation

“…C-terminal tagging and gene disruption were performed using PCR-generated fragments as described previously (Bähler et al, 1998; Sato et al, 2005). The minichromosome loss assay was carried out as described previously (Niwa et al, 1989; Tange et al, 2016). …”

Compositionally distinct nuclear pore complexes of functionally distinct dimorphic nuclei in the ciliate Tetrahymena

“…no. 600-401-215; Rockland Immunochemicals) at 1:200 dilution for 2 h, washed three times with PBS, then incubated with FluoroNano gold-conjugated anti-rabbit Fab′ also conjugated to Alexa Fluor 594 (Nanoprobes, Yaphank, NY) at 1:400 dilution for 1 h. The immunolabeled cells were fixed with 2.5% (w/v) glutaraldehyde (Nacalai tesque, Kyoto, Japan) for 1 h. After washing with 50 mM HEPES (pH 5.8), they were incubated with silver enhancement reagent (Tange et al, 2016) for 7 min. The reaction was stopped by washing three times with distilled water.…”