scholarly journals Extreme nuclear branching in healthy epidermal cells of the Xenopus tail fin

2018 ◽  
Author(s):  
Hannah E. Arbach ◽  
Marcus Harland-Dunaway ◽  
Jessica K. Chang ◽  
Andrea E. Wills
Keyword(s):  
Nuclear Lamina ◽  
Epidermal Cells ◽  
Dominant Negative ◽  
Nuclear Shape ◽  
Nuclear Morphology ◽  
Shape Variation ◽  
Tissue Elasticity ◽  
Filamentous Actin ◽  
Cell Cycles ◽  
Lamin B1

AbstractChanges in nuclear morphology contribute to regulation of complex cell properties, including differentiation and tissue elasticity. Perturbations of nuclear morphology are associated with pathologies that include, progeria, cancer, and muscular dystrophy. The mechanisms governing nuclear shape changes in healthy cells remain poorly understood, partially because there are few healthy models of nuclear shape variation. Here, we introduce nuclear branching in epidermal fin cells of Xenopus tropicalis as a model for extreme variation of nuclear morphology in a diverse population of healthy cells. We find that nuclear branching arises and elaborates during embryonic development. They contain broadly distributed marks of transcriptionally active chromatin and heterochromatin and have active cell cycles. We find that nuclear branches are disrupted by loss of filamentous actin and depend on epidermal expression of the nuclear lamina protein Lamin B1. Inhibition of nuclear branching disrupts fin morphology, suggesting that nuclear branching may be involved in fin development. This study introduces the nuclei of the fin as a powerful new model for extreme nuclear morphology in healthy cells to complement studies of nuclear shape variation in pathological contexts.List of abbreviations and symbolsLINC-Linker of Nucleoskeleton and Cytoskeleton, HGPS – Hutchinson-Gilford Progeria Syndrome, TEM – Transmission electron microscopy, PH3 – Phosphorylated Histone 3, Lat B – Latrunculin B, WT-Wild type, Cyto D-Cytochalasin D, Lmnb1 CRISPR – lmnb1 mutants generated by CRISPR/Cas9, E-Lmnb1 CRISPR – epidermal specific lmnb1 mutants generated by CRISPR/Cas9, Scrmbl-tadpoles injected with a scrambled version of the lmnb1 targeted sgRNA, Lmnb1-rod – dominant-negative Lamin B1 containing only the rod domainSummary StatementNuclei are highly branched throughout the heterogeneous population of healthy epidermal cells that comprise the Xenopus tail fin periphery, and disruption of nuclear branching mechanisms results in improper fin morphology.

scholarly journals Concentric organization of A- and B-type lamins predicts their distinct roles in the spatial organization and stability of the nuclear lamina

2019 ◽  
Vol 116 (10) ◽  
pp. 4307-4315 ◽  
Author(s):  
Bruce Nmezi ◽  
Jianquan Xu ◽  
Rao Fu ◽  
Travis J. Armiger ◽  
Guillermo Rodriguez-Bey ◽  
...  
Keyword(s):  
Spatial Organization ◽  
Critical Role ◽  
Nuclear Lamina ◽  
Nuclear Shape ◽  
Lamin A ◽  
Concentric Ring ◽  
Lamin B1 ◽  
Functional Consequences ◽  
Optical Reconstruction ◽  
Interacting Networks

The nuclear lamina is an intermediate filament meshwork adjacent to the inner nuclear membrane (INM) that plays a critical role in maintaining nuclear shape and regulating gene expression through chromatin interactions. Studies have demonstrated that A- and B-type lamins, the filamentous proteins that make up the nuclear lamina, form independent but interacting networks. However, whether these lamin subtypes exhibit a distinct spatial organization or whether their organization has any functional consequences is unknown. Using stochastic optical reconstruction microscopy (STORM) our studies reveal that lamin B1 and lamin A/C form concentric but overlapping networks, with lamin B1 forming the outer concentric ring located adjacent to the INM. The more peripheral localization of lamin B1 is mediated by its carboxyl-terminal farnesyl group. Lamin B1 localization is also curvature- and strain-dependent, while the localization of lamin A/C is not. We also show that lamin B1’s outer-facing localization stabilizes nuclear shape by restraining outward protrusions of the lamin A/C network. These two findings, that lamin B1 forms an outer concentric ring and that its localization is energy-dependent, are significant as they suggest a distinct model for the nuclear lamina—one that is able to predict its behavior and clarifies the distinct roles of individual nuclear lamin proteins and the consequences of their perturbation.

scholarly journals Deficiencies in lamin B1 and lamin B2 cause neurodevelopmental defects and distinct nuclear shape abnormalities in neurons

2011 ◽  
Vol 22 (23) ◽  
pp. 4683-4693 ◽  
Author(s):  
Catherine Coffinier ◽  
Hea-Jin Jung ◽  
Chika Nobumori ◽  
Sandy Chang ◽  
Yiping Tu ◽  
...  
Keyword(s):  
Knockout Mice ◽  
Neuronal Migration ◽  
Cortical Neurons ◽  
Nuclear Lamina ◽  
Nuclear Shape ◽  
Mammalian Brain ◽  
Asymmetric Distribution ◽  
Double Knockout ◽  
Lamin B1 ◽  
Deficient Mice

Neuronal migration is essential for the development of the mammalian brain. Here, we document severe defects in neuronal migration and reduced numbers of neurons in lamin B1–deficient mice. Lamin B1 deficiency resulted in striking abnormalities in the nuclear shape of cortical neurons; many neurons contained a solitary nuclear bleb and exhibited an asymmetric distribution of lamin B2. In contrast, lamin B2 deficiency led to increased numbers of neurons with elongated nuclei. We used conditional alleles for Lmnb1 and Lmnb2 to create forebrain-specific knockout mice. The forebrain-specific Lmnb1- and Lmnb2-knockout models had a small forebrain with disorganized layering of neurons and nuclear shape abnormalities, similar to abnormalities identified in the conventional knockout mice. A more severe phenotype, complete atrophy of the cortex, was observed in forebrain-specific Lmnb1/Lmnb2 double-knockout mice. This study demonstrates that both lamin B1 and lamin B2 are essential for brain development, with lamin B1 being required for the integrity of the nuclear lamina, and lamin B2 being important for resistance to nuclear elongation in neurons.

scholarly journals Loss of lamin-B1 and defective nuclear morphology are hallmarks of astrocyte senescence in vitro and in the aging human hippocampus

2021 ◽  
Author(s):  
Isadora Matias ◽  
Luan Pereira Diniz ◽  
Isabella Vivarini Damico ◽  
Laís da Silva Neves ◽  
Ana Paula Bergamo Araujo ◽  
...  
Keyword(s):  
Nuclear Lamina ◽  
Granular Cell ◽  
Significant Loss ◽  
Nuclear Morphology ◽  
Post Mortem ◽  
Human Brain Tissue ◽  
Lamin B1 ◽  
Human Hippocampus ◽  
Age Related

ABSTRACTThe increase in senescent cells in tissues, including the brain, is a general feature of normal aging and age-related pathologies. Senescent cells exhibit a specific phenotype, which includes an altered nuclear morphology and transcriptomic changes. Astrocytes undergo senescence in vitro and in age-associated neurodegenerative diseases, but little is known about whether this process also occurs in physiological aging. Here, we investigated astrocyte senescence in vitro, in old mouse brains and in post-mortem human brain tissue of elderly. We identified a significant loss of lamin-B1, a major component of the nuclear lamina, as a hallmark of senescent astrocytes. We showed a severe reduction of lamin-B1 in the dentate gyrus of aged mice, including in hippocampal astrocytes, and in the granular cell layer of the hippocampus of post-mortem human tissue from non-demented elderly. Interestingly, the lamin-B1 reduction was associated with nuclear deformations, represented by an increased incidence of invaginated nuclei and loss of nuclear circularity in senescent astrocytes in vitro and in the aging human hippocampus. In conclusion, our findings show that reduction of lamin-B1 is a conserved hallmark of astrocyte aging, as well as shed light on significant defects in nuclear lamina structure, which may impact astrocyte function during human aging.

scholarly journals Farnesylated Nuclear Proteins Kugelkern and Lamin Dm0 Affect Nuclear Morphology by Directly Interacting with the Nuclear Membrane

2010 ◽  
Vol 21 (19) ◽  
pp. 3409-3420 ◽  
Author(s):  
Maria Polychronidou ◽  
Andrea Hellwig ◽  
Jörg Grosshans
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Nuclear Lamina ◽  
Nuclear Shape ◽  
Phospholipid Bilayer ◽  
Nuclear Morphology ◽  
Filament Formation ◽  
Terminal Part ◽  
Pathological Conditions ◽  
Shape Changes

Nuclear shape changes are observed during a variety of developmental processes, pathological conditions, and ageing. The mechanisms underlying nuclear shape changes in the above-mentioned situations have mostly remained unclear. To address the molecular mechanism behind nuclear shape changes, we analyzed how the farnesylated nuclear envelope proteins Kugelkern and lamin Dm0 affect the structure of the nuclear membrane. We found that Kugelkern and lamin Dm0 affect nuclear shape without requiring filament formation or the presence of a classical nuclear lamina. We also could show that the two proteins do not depend on a group of selected inner nuclear membrane proteins for their localization to the nuclear envelope. Surprisingly, we found that farnesylated Kugelkern and lamin Dm0 protein constructs change the morphology of protein-free liposomes. Based on these findings, we propose that farnesylated proteins of the nuclear membrane induce nuclear shape changes by being asymmetrically inserted into the phospholipid bilayer via their farnesylated C-terminal part.

scholarly journals Lamin B1 acetylation slows the G1 to S cell cycle transition through inhibition of DNA repair

2021 ◽  
Author(s):  
Laura A Murray-Nerger ◽  
Joshua L Justice ◽  
Pranav Rekapalli ◽  
Josiah E Hutton ◽  
Ileana M Cristea
Keyword(s):  
Cell Cycle ◽  
Dna Repair ◽  
Posttranslational Modifications ◽  
Cell Cycle Progression ◽  
Nuclear Periphery ◽  
Virus Production ◽  
Nuclear Lamina ◽  
Regulatory Function ◽  
Herpesvirus Type ◽  
Lamin B1

Abstract The integrity and regulation of the nuclear lamina is essential for nuclear organization and chromatin stability, with its dysregulation being linked to laminopathy diseases and cancer. Although numerous posttranslational modifications have been identified on lamins, few have been ascribed a regulatory function. Here, we establish that lamin B1 (LMNB1) acetylation at K134 is a molecular toggle that controls nuclear periphery stability, cell cycle progression, and DNA repair. LMNB1 acetylation prevents lamina disruption during herpesvirus type 1 (HSV-1) infection, thereby inhibiting virus production. We also demonstrate the broad impact of this site on laminar processes in uninfected cells. LMNB1 acetylation negatively regulates canonical nonhomologous end joining by impairing the recruitment of 53BP1 to damaged DNA. This defect causes a delay in DNA damage resolution and a persistent activation of the G1/S checkpoint. Altogether, we reveal LMNB1 acetylation as a mechanism for controlling DNA repair pathway choice and stabilizing the nuclear periphery.

scholarly journals An RNAi screen for genes that affect nuclear morphology in Caenorhabditis elegans reveals the involvement of unexpected processes

2021 ◽  
Author(s):  
Richa Maheshwari ◽  
Mohammad M Rahman ◽  
Daphna Joseph-Strauss ◽  
Orna Cohen-Fix
Keyword(s):  
Caenorhabditis Elegans ◽  
Nuclear Pore Complex ◽  
Cellular Transformation ◽  
Rnai Screen ◽  
Nuclear Shape ◽  
Nuclear Pore ◽  
Nuclear Morphology ◽  
Anaphase Bridges ◽  
Early Embryos ◽  
Embryonic Viability

Abstract Aberration in nuclear morphology is one of the hallmarks of cellular transformation. However, the processes that, when mis-regulated, result aberrant nuclear morphology are poorly understood. In this study we carried out a systematic, high-throughput RNAi screen for genes that affect nuclear morphology in Caenorhabditis elegans embryos. The screen employed over 1700 RNAi constructs against genes required for embryonic viability. Nuclei of early embryos are typically spherical, and their NPCs are evenly distributed. The screen was performed on early embryos expressing a fluorescently tagged component of the nuclear pore complex (NPC), allowing visualization of nuclear shape as well as the distribution of NPCs around the nuclear envelope. Our screen uncovered 182 genes whose down-regulation resulted in one or more abnormal nuclear phenotypes, including multiple nuclei, micronuclei, abnormal nuclear shape, anaphase bridges and abnormal NPC distribution. Many of these genes fall into common functional groups, including some that were not previously known to affect nuclear morphology, such as genes involved in mitochondrial function, the vacuolar ATPase and the CCT chaperonin complex. The results of this screen add to our growing knowledge of processes that affect nuclear morphology and that may be altered in cancer cells that exhibit abnormal nuclear shape.

scholarly journals Lamin B1 and lamin B2 are long-lived proteins with distinct functions in retinal development

2016 ◽  
Vol 27 (12) ◽  
pp. 1928-1937 ◽  
Author(s):  
David Razafsky ◽  
Candace Ward ◽  
Chloe Potter ◽  
Wanqiu Zhu ◽  
Yunlu Xue ◽  
...  
Keyword(s):  
Nuclear Lamina ◽  
Building Blocks ◽  
Postnatal Life ◽  
Cone Photoreceptors ◽  
Obvious Effect ◽  
Lamin B1 ◽  
Embryonic Neurogenesis ◽  
And Function ◽  
Embryonic Retina ◽  
Rod And Cone Photoreceptors

Lamin B1 and lamin B2 are essential building blocks of the nuclear lamina, a filamentous meshwork lining the nucleoplasmic side of the inner nuclear membrane. Deficiencies in lamin B1 and lamin B2 impair neurodevelopment, but distinct functions for the two proteins in the development and homeostasis of the CNS have been elusive. Here we show that embryonic depletion of lamin B1 in retinal progenitors and postmitotic neurons affects nuclear integrity, leads to the collapse of the laminB2 meshwork, impairs neuronal survival, and markedly reduces the cellularity of adult retinas. In stark contrast, a deficiency of lamin B2 in the embryonic retina has no obvious effect on lamin B1 localization or nuclear integrity in embryonic retinas, suggesting that lamin B1, but not lamin B2, is strictly required for nucleokinesis during embryonic neurogenesis. However, the absence of lamin B2 prevents proper lamination of adult retinal neurons, impairs synaptogenesis, and reduces cone photoreceptor survival. We also show that lamin B1 and lamin B2 are extremely long-lived proteins in rod and cone photoreceptors. OF interest, a complete absence of both proteins during postnatal life has little or no effect on the survival and function of cone photoreceptors.

scholarly journals Concentration-dependent lamin assembly and its roles in the localization of other nuclear proteins

2014 ◽  
Vol 25 (8) ◽  
pp. 1287-1297 ◽  
Author(s):  
Yuxuan Guo ◽  
Youngjo Kim ◽  
Takeshi Shimi ◽  
Robert D. Goldman ◽  
Yixian Zheng
Keyword(s):  
Nuclear Lamina ◽  
Nuclear Pore ◽  
Lamin A ◽  
Nuclear Pore Complexes ◽  
Developmental Defects ◽  
Protein Levels ◽  
Lamin B1 ◽  
Mouse Cells ◽  
Pore Complexes ◽  
And Function

The nuclear lamina (NL) consists of lamin polymers and proteins that bind to the polymers. Disruption of NL proteins such as lamin and emerin leads to developmental defects and human diseases. However, the expression of multiple lamins, including lamin-A/C, lamin-B1, and lamin-B2, in mammals has made it difficult to study the assembly and function of the NL. Consequently, it has been unclear whether different lamins depend on one another for proper NL assembly and which NL functions are shared by all lamins or are specific to one lamin. Using mouse cells deleted of all or different combinations of lamins, we demonstrate that the assembly of each lamin into the NL depends primarily on the lamin concentration present in the nucleus. When expressed at sufficiently high levels, each lamin alone can assemble into an evenly organized NL, which is in turn sufficient to ensure the even distribution of the nuclear pore complexes. By contrast, only lamin-A can ensure the localization of emerin within the NL. Thus, when investigating the role of the NL in development and disease, it is critical to determine the protein levels of relevant lamins and the intricate shared or specific lamin functions in the tissue of interest.

FGF signals are involved in the differentiation of notochord cells and mesenchyme cells of the ascidianHalocynthia roretzi

Development ◽  
2001 ◽  
Vol 128 (14) ◽  
pp. 2711-2721 ◽  
Author(s):  
Yoshie Shimauchi ◽  
Seiko D. Murakami ◽  
Nori Satoh
Keyword(s):  
Receptor Gene ◽  
Epidermal Cells ◽  
Dominant Negative ◽  
Tyrosine Kinase Domain ◽  
Fgf Receptor ◽  
Dominant Negative Form ◽  
Notochord Cells ◽  
Mesenchyme Cells ◽  
Endodermal Cells ◽  
Negative Form

Differentiation of notochord cells and mesenchyme cells of the ascidian Halocynthia roretzi requires interactions with neighboring endodermal cells and previous experiments suggest that these interactions require fibroblast growth factor (FGF). In the present study, we examined the role of FGF in these interactions by disrupting signaling using the dominant negative form of the FGF receptor. An FGF receptor gene of H. roretzi (HrFGFR) is expressed both maternally and zygotically. The maternally expressed transcript was ubiquitously distributed in fertilized eggs and in early embryos. Zygotic expression became evident by the neurula stage and transcripts were detected in epidermal cells of the posterior half of embryos. Synthetic mRNA for the dominant negative form of FGFR, in which the intracellular tyrosine kinase domain was deleted, was injected into fertilized eggs to interfere with the possible function of HrFGFR. Injected eggs cleaved and gastrulated the same as the control embryos. Analyses of the expression of differentiation markers in the experimental embryos indicated that the differentiation of epidermal cells, muscle cells and endodermal cells was not affected significantly. However, manipulated embryos showed downregulation of notochord-specific Brachyury expression and failure of notochord cell differentiation, resulting in the development of tailbud embryos with shorted tails. The expression of an actin gene that is normally expressed in mesenchyme cells was also suppressed. These results suggest that FGF signals are involved in differentiation of notochord cells and mesenchyme cells in Halocynthia embryos. Furthermore, the patterning of a neuron-specific tubulin gene expression was disturbed, suggesting that the formation of the nervous system was directly affected by disrupting FGF signals or indirectly affected due to the disruption of normal notochord formation.

Mutations inDrosophila myblead to centrosome amplification and genomic instability

Development ◽  
2002 ◽  
Vol 129 (2) ◽  
pp. 347-359 ◽  
Author(s):  
Siau-Min Fung ◽  
Gary Ramsay ◽  
Alisa L. Katzen
Keyword(s):  
Cell Cycle ◽  
Epidermal Cells ◽  
Loss Of Function ◽  
Brca1 And Brca2 ◽  
Cell Cycles ◽  
Myb Gene ◽  
Pupal Wing ◽  
Complete Cell ◽  
Abnormal Mitoses ◽  
Mutant Cells

We have previously established that the single myb gene in Drosophila melanogaster, Dm myb, which is related to the proto-oncogene Myb, is required for the G2/M transition of the cell cycle and for suppression of endoreduplication in pupal wing cells. We now report that studies of the abdominal phenotype in loss-of-function Dm myb mutants reveal additional roles for Dm myb in the cell cycle, specifically in mitosis. Abdominal epidermal cells that are mutant for Dm myb proliferate more slowly than wild-type controls throughout pupation, with particularly sluggish progression through the early stages of mitosis. Abnormal mitoses associated with multiple functional centrosomes, unequal chromosome segregation, formation of micronuclei, and/or failure to complete cell division are common in the later cell cycles of mutant cells. Resulting nuclei are often aneuploid and/or polyploid. Similar defects have also been observed in loss-of-function mutations of the tumor suppressor genes p53, Brca1 and Brca2. These data demonstrate that in abdominal epidermal cells, Dm myb is required to sustain the appropriate rate of proliferation, to suppress formation of supernumerary centrosomes, and to maintain genomic integrity.

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