What drives nuclear growth? Studying nuclei assembled in Xenopus egg extract and focusing on importin α/β-mediated nuclear import, we show that, while import is required for nuclear growth, nuclear growth and import can be uncoupled when chromatin structure is manipulated. Nuclei treated with micrococcal nuclease to fragment DNA grew slowly despite exhibiting little to no change in import rates. Nuclei assembled around axolotl chromatin with 20-fold more DNA than Xenopus grew larger but imported more slowly. Treating nuclei with reagents known to alter histone methylation or acetylation caused nuclei to grow less while still importing to a similar extent or to grow larger without significantly increasing import. Nuclear growth but not import was increased in live sea urchin embryos treated with the DNA methylator N-nitrosodimethylamine. These data suggest that nuclear import is not the primary driving force for nuclear growth. Instead, we observed that nuclear blebs expanded preferentially at sites of high chromatin density and lamin addition, whereas small Benzonase-treated nuclei lacking DNA exhibited reduced lamin incorporation into the nuclear envelope. In summary, we report experimental conditions where nuclear import is not sufficient to drive nuclear growth, hypothesizing that this uncoupling is a result of altered chromatin structure.

The nuclear lamina is a complex network of nuclear lamins and lamin-associated nuclear membrane proteins, which scaffold the nucleus to maintain structural integrity. In Arabidopsis thaliana, nuclear matrix constituent proteins (NMCPs) are essential components of the nuclear lamina and are required to maintain the structural integrity of the nucleus and specific perinuclear chromatin anchoring. At the nuclear periphery, suppressed chromatin overlapping with repetitive sequences and inactive protein-coding genes are enriched. At a chromosomal level, plant chromatin organization in interphase nuclei is flexible and responds to various developmental cues and environmental stimuli. On the basis of these observations in Arabidopsis, and given the role of NMCP genes (CRWN1 and CRWN4) in organizing chromatin positioning at the nuclear periphery, one can expect considerable changes in chromatin-nuclear lamina interactions when the global chromatin organization patterns are being altered in plants. Here we report the highly flexible nature of the plant nuclear lamina, which disassembles substantially under various stress conditions. Focusing on heat stress, we reveal that chromatin domains, initially tethered to the nuclear envelope, remain largely associated with CRWN1 and become scattered in the inner nuclear space. By investigating the three-dimensional chromatin contact network, we further reveal that CRWN1 proteins play a structural role in shaping the changes in genome folding under heat stress. Also, CRWN1 acts as a negative transcriptional coregulator to modulate the shift of the plant transcriptome profile in response to heat stress.

Plants cope with various recurring stress conditions that often induce DNA damage, ultimately affecting plant genome integrity, growth, and productivity. The CROWDED NUCLEI (CRWN) family comprises lamin-like proteins with multiple functions, such as regulating gene expression, genome organization, and DNA damage repair in Arabidopsis (Arabidopsis thaliana). However, the mechanisms and consequences of CRWNs in DNA damage repair are largely unknown. Here, we reveal that CRWNs maintain genome stability by forming repairing nuclear bodies at DNA double-strand breaks. We demonstrate that CRWN1 and CRWN2 physically associate with the DNA damage repair proteins RAD51D and SUPPRESSOR OF NPR1-1 Inducible 1 (SNI1) and act in the same genetic pathway to mediate this process. Moreover, CRWN1 and CRWN2 partially localize at γ-H2AX foci upon DNA damage. Notably, CRWN1 and CRWN2 undergo liquid-liquid phase separation to form highly dynamic droplet-like structures with RAD51D and SNI1 to promote the DNA damage response (DDR). Collectively, our data shed light on the function of plant lamin-like proteins in the DDR and maintenance of genome stability.

To facilitate survival, replication, and dissemination, the intracellular pathogen Legionella pneumophila relies on its unique type IVB secretion system (T4SS) to deliver over 330 effectors to hijack host cell pathways in a spatiotemporal manner. The effectors and their host targets are largely unexplored due to their low sequence identity to the known proteins and functional redundancy. The T4SS effector SidN (Lpg1083) is secreted into host cells during the late infection period. However, to the best of our knowledge, the molecular characterization of SidN has not been studied. Herein, we identified SidN as a nuclear envelope-localized effector. Its structure adopts a novel fold, and the N-terminal domain is crucial for its specific subcellular localization. Furthermore, we found that SidN is transported by eukaryotic karyopherin Importin-13 into the nucleus, where it attaches to the N-terminal region of Lamin-B2 to interfere with the integrity of the nuclear envelope, causing nuclear membrane disruption and eventually cell death. Our work provides new insights into the structure and function of an L. pneumophila effector protein, and suggests a potential strategy utilized by the pathogen to promote host cell death and then escape from the host for secondary infection.

\"Laminopathies\" refers to a wide spectrum of myopathies caused by mutations in the LMNA gene. These myopathies include limb girdle muscular dystrophy type 1B (LGMD1B) and dilated cardiomyopathy 1 A (DCM1A), which are both autosomal dominant neurogenetic diseases. There have been few studies on mosaicism in laminopathies. Herein, a Han Chinese family with laminopathies was enrolled in our study. Genetic analysis revealed that the proband carried a novel splice site mutation, c. 1158-3 C > T, in the LMNA gene due to her mother having de novo somatic and gonadal mosaicism. Reverse-transcription polymerase chain reaction (RT-PCR) analysis revealed reduced levels of LMNA mRNA in the proband, which were probably due to nonsense-mediated mRNA decay (NMD). Western blotting revealed reduced lamin A/C protein levels in the skeletal muscle tissue of the proband. In this family, the clinical phenotypes of the proband\'s mother were normal, and the c. 1158-3 C > T splicing mutation was identified in the blood sample of the proband\'s mother. Thus, the mutation could be easily considered to be nonpathogenic. Our study emphasizes the importance of mosaicism in the identification of pathogenic variants and genetic counseling.

Lamins are the ancient type V intermediate filament proteins contributing to diverse biological functions, such as the maintenance of nuclear morphology, stabilization of chromatin architecture, regulation of cell cycle progression, regulation of spatial-temporal gene expressions, and transduction of mechano-signaling. Deregulation of lamins is associated with abnormal nuclear morphology and chromatin disorganization, leading to a variety of diseases such as laminopathy and premature aging, and might also play a role in cancer. Accumulating evidence indicates that lamins are functionally regulated by post-translational modifications (PTMs) including farnesylation, phosphorylation, acetylation, SUMOylation, methylation, ubiquitination, and O-GlcNAcylation that affect protein stabilization and the association with chromatin or associated proteins. The mechanisms by which these PTMs are modified and the relevant functionality become increasingly appreciated as understanding of these changes provides new insights into the molecular mechanisms underlying the laminopathies concerned and novel strategies for the management. In this review, we discussed a range of lamin PTMs and their roles in both physiological and pathological processes, as well as potential therapeutic strategies by targeting lamin PTMs.

OBJECTIVE: We evaluated left atrial (LA) remodeling using cardiac MRI (CMR) in patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer during and after trastuzumab therapy.
METHODS: In this prospective 2-center longitudinal study, 41 women with HER2-positive breast cancer received adjuvant trastuzumab for 12 months, in addition to standard chemotherapy. Serial CMRs were performed at baseline, 6, 12, and 18 months after initiation of trastuzumab. LA volumes were measured by a blinded reader. Linear mixed model was used to evaluate longitudinal changes.
RESULTS: Of 41 women (mean age 52 ± 11 [SD] years; 56% received anthracycline), one patient experienced trastuzumab-induced cardiotoxicity (TIC) for which trastuzumab was interrupted for one cycle. Mean baseline left ventricular ejection fraction (LVEF) was 68.0 ± 5.9% and LA ejection fraction (LAEF) was 66.0 ± 6.6%. Compared to baseline, LAEF decreased significantly at 6 months (62.7 ± 5.7%, p = 0.027) and 12 months (62.2 ± 6.1%, p = 0.003), while indexed LA minimum volume (LAmin) significantly increased at 12 months (11.6 ± 4.9 ml/m2 vs 13.8 ± 4.5 ml/m2, p = 0.002). At 18 months, all changes from baseline were no longer significant. From baseline to 6 months, change in LAEF correlated with change in LVEF (Spearman\'s r = 0.41, p = 0.014). No significant interactions (all p > 0.10) were detected between time and anthracycline use for LA parameters.
CONCLUSIONS: Among trastuzumab-treated patients with low incidence of TIC, we observed a small but significant decline in LAEF and increase in LAmin that persisted for the duration of therapy and recovered 6 months after therapy cessation. These findings suggest that trastuzumab has concurrent detrimental effects on atrial and ventricular remodeling.
CONCLUSIONS: • In trastuzumab-treated breast cancer patients evaluated by cardiac MRI, left atrial ejection fraction declined and minimum volume increased during treatment and recovered to baseline after trastuzumab cessation. • Changes in left atrial ejection fraction correlated with changes in left ventricular ejection fraction in the first 6 months of trastuzumab treatment. • Trastuzumab therapy is associated with concurrent detrimental effects on left atrial and ventricular remodeling.

Glioma is the most common type of tumor in the central nervous system, accounting for around 80% of all malignant brain tumors. Previous studies showed a significant association between nuclear morphology and the malignant progress of gliomas. By virtue of integrated proteomics and genomics analyses as well as experimental validations, we identify three nuclear lamin genes (LMNA, LMNB1 and LMNB2) that are significantly upregulated in glioma tissues compared with normal brain tissues. We show that elevated expressions of LMNB1, LMNB2 and LMNA in glioma cells are highly associated with the rapid progression of the disease and the knockdown of LMNB1, LMNB2 and LMNA dramatically suppresses glioma progression in both in vitro and in vivo mouse models. Moreover, the repression of glioma cell growth by lamin knockdown is mediated by the pRb-mediated G1-S inhibition. On the contrary, overexpression of lamins in normal human astrocytes dramatically induced nuclear morphological aberrations and accelerated cell growth. Together, our multi-omics-based analysis has revealed a previously unrecognized role of lamin genes in gliomagenesis, providing a strong support for the key link between aberrant tumor nuclear shape and the survival of glioma patients. Based on these findings, lamins are proposed to be potential oncogene targets for therapeutic treatments of brain tumors.

The chromatin fiber folds into loops, but the mechanisms controlling loop extrusion are still poorly understood. Using super-resolution microscopy, we visualize that loops in intact nuclei are formed by a scaffold of cohesin complexes from which the DNA protrudes. RNA polymerase II decorates the top of the loops and is physically segregated from cohesin. Augmented looping upon increased loading of cohesin on chromosomes causes disruption of Lamin at the nuclear rim and chromatin blending, a homogeneous distribution of chromatin within the nucleus. Altering supercoiling via either transcription or topoisomerase inhibition counteracts chromatin blending, increases chromatin condensation, disrupts loop formation, and leads to altered cohesin distribution and mobility on chromatin. Overall, negative supercoiling generated by transcription is an important regulator of loop formation in vivo.

Neural stem/progenitor cells (NSPCs) persist over the lifespan while encountering constant challenges from age or injury related brain environmental changes like elevated oxidative stress. But how oxidative stress regulates NSPC and its neurogenic differentiation is less clear. Here we report that acutely elevated cellular oxidative stress in NSPCs modulates neurogenic differentiation through induction of Forkhead box protein O3 (FOXO3)-mediated cGAS/STING and type I interferon (IFN-I) responses. We show that oxidative stress activates FOXO3 and its transcriptional target glycine-N-methyltransferase (GNMT) whose upregulation triggers depletion of s-adenosylmethionine (SAM), a key co-substrate involved in methyl group transfer reactions. Mechanistically, we demonstrate that reduced intracellular SAM availability disrupts carboxymethylation and maturation of nuclear lamin, which induce cytosolic release of chromatin fragments and subsequent activation of the cGAS/STING-IFN-I cascade to suppress neurogenic differentiation. Together, our findings suggest the FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signaling cascade as a critical stress response program that regulates long-term regenerative potential.