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PubMed2001

TUNEL staining and electron microscopy studies of apoptotic changes in the guinea pig vallate taste cells after unilateral glossopharyngeal denervation.

On the basis of our previous report that unilateral glossopharyngeal neurectomy in the guinea pig resulted in degeneration and disappearance of taste buds in ipsilateral vallate papillae (Huang and Lu 1996), it is reasonable to speculate that gustatory denervation may enhance apoptosis of taste bud cells, with taste buds decreasing in number and ultimately disappearing after neurectomy. We were therefore determined to investigate apoptosis of taste bud cells in guinea pig vallate papillae after unilateral glossopharyngeal neurectomy using both terminal deoxynuleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) at the light microscopic level and by conventional electron microscopy. A total of 34 adult guinea pigs were unilaterally glossopharyngeal-neurectomized and sacrificed at 3, 6, 12 h and 1, 3 and 7 days after surgery. The results revealed that only a very few TUNEL-positive nuclei indicating apoptosis were present in normal taste buds, but in surgically denervated papillae, they increased in number from 6 h-12 h after surgery, reached at peak on day 1 and then gradually decreased. In apoptotic cells from normal taste buds, electron microscopy revealed condensation of the chromatin against the nuclear envelope, changes in the nuclear envelope, and fragmentation of the nucleus, but the integrity of the plasma membrane and organelles was maintained. Neurectomized taste cells were also characterized by condensed and fragmentary nuclei, compactness of the cytoplasmic organelles, and the appearance of pedunculated protuberances on the cell surface. From these observations, we conclude that: (1) glossopharyngeal neurectomy enhanced apoptosis of vallate taste bud cells in guinea pig; (2) appropriate gustatory nerve innervation is an essential component for the maintenance of the taste bud, and may play a role in apoptosis of taste cells.

Animals↗
PubMed1987

Reversible inhibition of protein import into the nucleus by wheat germ agglutinin injected into cultured cells.

The importance of glycoproteins located in the nuclear envelope in nuclear transport was tested by microinjection of karyophilic proteins into the cytoplasm of cultured human cells together with various lectins. Wheat germ agglutinin (WGA) blocked the nuclear transport of nucleoplasmin, a nuclear protein of Xenopus laevis oocytes, and of nonnuclear proteins conjugated with a synthetic peptide containing the nuclear localization signal sequence for simian virus 40 (SV40) large T antigen. Its inhibitory activity persisted for about 1 h after its injection into the cells and then gradually decreased. Export of at least some kinds of RNA from the nucleus seemed not to be affected by WGA even when import of the proteins into the nucleus was completely blocked (within 1 h after WGA injection). Moreover, WGA did not inhibit the passive diffusion of fluorescein isothiocyanate (FITC)-dextran (average Mr 17,900) into the nucleus. Wistaria floribunda agglutinin (WFA), concanavalin A (Con A), and lentil lectin did not block nuclear transport. These results indicate that WGA specifically blocks active protein import, but not passive diffusion of materials into the nucleus.

Antigens, Polyomavirus Transforming↗
PubMed1991

How proteins enter the nucleus.

Nuclear protein import is a selective process. Proteins destined for the nucleus contain NLSs. These short stretches of amino acids interact with proteins located in the cytoplasm, on the nuclear envelope, and/or at the nuclear pore complex. Following binding at the pore complex, proteins are translocated through the pore into the nucleus in a manner requiring ATP. The biochemical dissection of the nuclear pore complex has begun. Alteration of protein import into the nucleus is emerging as a new and complex form of regulation. However, we are left with the following problems: How do proteins move through the cytoplasm to reach the nuclear pore? How does the nuclear pore complex open and close in a selective manner? How is ATP utilized during import? And finally, how is bi-directional traffic of both proteins and RNA through the pore regulated?

Adenosine Triphosphate↗
PubMed2005

Cloning and characterization of rat importin 9: implication for its neuronal function.

We describe the structure of the rat importin 9 gene, together with its transcripts and the encoded protein with its putative functional domains. The importin 9 gene contains 24 exons in a genomic region spanning >52,000 bp. It is transcribed into two mRNAs, generated by means of alternative polyadenylation site usage arranged in tandem. Both transcripts possess the same noncanonical polyadenylation signal (AGUAAA) in rat, this hexamer being conserved in all vertebrates examined. Additionally, intron 8 is bordered by AT-AC dinucleotides. Importin 9 is expressed throughout adult rat tissues, but the 114-kDa Importin 9 protein was detected only in the brain. The localization of the Importin 9 protein was examined by immunohistochemistry in both adult rat tissues and primary hippocampal cell cultures. The strongest labeling was detected in vivo in areas populated by neurons in high density and also in the dendritic processes emanating from these cells. This protein was clearly concentrated in the nuclei of these cells, although their cytoplasms too were heavily labeled. Strong cytoplasmic and very strong nuclear staining was found in a vast majority of the cells with neuronal morphology in vitro. Cultured cells with glial morphology generally exhibited a weaker cytoplasmic labeling. In these cells, the signal decorated the nuclear envelope without nuclear staining and gradually dwindled toward the cell periphery. These results hint at the cell- or tissue-type specific functions of this type of importin protein.

Amino Acid Sequence↗
PubMed2004

Intracellular assembly and sorting of intermediate filament proteins: role of the 42 amino acid lamin insert.

Nuclear and cytoplasmic intermediate filament (IF) proteins segregate into two independent cellular networks by mechanisms that are poorly understood. We examined the role of a 42 amino acid (aa) insert unique to vertebrate lamin rod domains in the coassembly of nuclear and cytoplasmic IF proteins by overexpressing chimeric IF proteins in human SW13+ and SW13- cells, which contain and lack endogenous cytoplasmic IF proteins, respectively. The chimeric IF proteins consisted of the rod domain of human nuclear lamin A/C protein fused to the amino and carboxyl-terminal domains of the mouse neurofilament light subunit (NF-L), which contained or lacked the 42 aa insert. Immunofluorescence microscopy was used to follow assembly and targeting of the proteins in cells. Chimeric proteins that lacked the 42 aa insert colocalized with vimentin, whereas those that contained the 42 aa insert did not. When overexpressed in SW13- cells, chimeric proteins containing the 42 aa formed very short or broken cytoplasmic filaments, whereas chimeric proteins that lacked the insert assembled efficiently into long, stable cytoplasmic filaments. To examine the roles of other structural motifs in intracellular targeting, we added two additional sequences to the chimera, a nuclear localization signal (NLS) and a CAAX motif, which are found in nuclear IF proteins. Addition of an NLS alone or an NLS in combination with the CAAX motif to the chimera with the 42 aa insert resulted in cagelike filament that assembled close to the nuclear envelope and nuclear lamina-like targeting, respectively. Our results suggest that the rod domains of eukaryotic nuclear and cytoplasmic IF proteins, which are related to each other, are still compatible upon deletion of the 42 aa insert of coassembly. In addition, NF-L end domains can substitute for the corresponding lamin domains in nuclear lamina targeting.

Amino Acid Sequence↗
PubMed2005

A Bpag1 isoform involved in cytoskeletal organization surrounding the nucleus.

Bpag1/dystonin proteins are giant cytoskeletal interacting proteins postulated to cross-link cytoskeletal filaments and thereby maintain cellular integrity. Loss of function of non-epithelial Bpag1 isoforms results in neuromuscular dysfunction and early postnatal death in mice. Multiple Bpag1 transcripts have been described, including those encoding protein isoforms that vary at the N-terminal end. Here, we have analyzed the subcellular localizations and cytoskeletal interactions of two isoforms, termed Bpag1a1 and Bpag1a2. We demonstrate that novel sequence at the 5' end of the Bpag1a2 transcript codes for an N-terminal transmembrane domain and targets the protein to the perinuclear region of the cell. Furthermore, we show that the endogenous Bpag1a2 protein is also present in the perinuclear region in myoblast cells. Differences in Bpag1a1 and Bpag1a2 with respect to the extent of their interactions with microtubules and microfilaments are also described, with Bpag1a2 fusion protein serving largely to associate with microfilaments surrounding the nucleus and Golgi apparatus. The overall structure and subcellular localizations of Bpag1a2 indicate possible functions in nuclear envelope structuring, nuclear tethering, and organization of membranous structures surrounding the nucleus.

Actins↗
PubMed2000

Paternal contributions to the mammalian zygote: fertilization after sperm-egg fusion.

Mammalian fertilization has traditionally been regarded as a simple blending of two gametes, during which the haploid genome of the fertilizing spermatozoon constitutes the primary paternal contribution to the resulting embryo. In contrast to this view, new research provides evidence of important cytoplasmic contributions made by the fertilizing spermatozoon to the zygotic makeup, to the organization of preimplantation development, and even reproductive success of new forms of assisted fertilization. The central role of the sperm-contributed centriole in the reconstitution of zygotic centrosome has been established in most mammalian species and is put in contrast with strictly maternal centrosomal inheritance in rodents. The complementary reduction or multiplication of sperm and oocyte organelles during gametogenesis, exemplified by the differences in the biogenesis of centrosome in sperm and oocytes, represents an intriguing mechanism for avoiding their redundancy during early embryogenesis. New studies on perinuclear theca of sperm revealed its importance for both spermatogenesis and fertilization. Remodeling of the sperm chromatin into a male pronucleus is guided by oocyte-produced, reducing peptide glutathione and a number of molecules required for the reconstitution of the functional nuclear envelope and nuclear skeleton. Although some of the sperm structures are transformed into zygotic components, the elimination of others is vital to early stages of embryonic development. Sperm mitochondria, carrying potentially harmful paternal mtDNA, appear to be eliminated by a ubiquitin-dependent mechanism. Other accessory structures of the sperm axoneme, including fibrous sheath, microtubule doublets, outer dense fibers, and the striated columns of connecting piece, are discarded in an orderly fashion. The new methods of assisted fertilization, represented by intracytoplasmic sperm injection and round spermatid injection, bypass multiple steps of natural fertilization by introducing an intact spermatozoon or spermatogenic cell into oocyte cytoplasm. Consequently, the carryover of sperm accessory structures that would normally be eliminated before or during the entry of sperm into oocyte cytoplasm persist therein and may interfere with early embryonic development, thus decreasing the success rate of assisted fertilization and possibly causing severe embryonic anomalies. Similarly, foreign organelles, proteins, messenger RNAs, and mitochondrial DNAs, which may have a profound impact on the embryonic development, are propagated by the nuclear transfer of embryonic blastomeres and somatic cell nuclei. This aspect of assisted fertilization is yet to be explored by a focused effort.

Cell Membrane↗
PubMed2003

Assembly of yolk spindles in the early Drosophila embryo.

The development of the early Drosophila embryo is marked by the separation of two nuclear lineages, yolk and somatic nuclei, each having its own division program despite residing in a common cytoplasm. We show that the failure of nuclear division of the yolk nuclei is a consequence of dysfunction in bipolar spindle organization during mitosis 10 and 11. Yolk spindle organization defects are directly correlated to centrosome behaviour, which is abnormal in at least three sequential aspects. First, the yolk centrosomes do not migrate properly along the nuclear envelope during nuclear cycles 10 and 11 and give rise to non-functional monopolar spindles. Second, the centrosomes detached from the poles spindle at the end of nuclear cycle 11, leaving the spindles anastral. Third, the free centrosomes duplicate in the absence of nuclear division during last mitoses and early gastrulation, but do not separate properly. In spite of their reduced nucleating properties, beyond the nuclear cycle 12, the yolk centrosomes contain typical centrosomal antigens, suggesting that their structural organization has not been changed after they disperse in the cytoplasm. Our findings also demonstrate that the centrosome dynamics are spatially and temporally regulated in the yolk region. This observation is consistent with the presence of rate-limiting levels of maternally provided key molecular components, needed for centrosome duplication and positioning. The presence of normal and abnormal centrosomes in the same cytoplasm provides an useful model for investigating the common regulators of the nucleus and centrosome cycle which ensure precise spindle pole duplication.

Animals↗
PubMed2003

Antinuclear antibodies specific for primary biliary cirrhosis.

The serological hallmark of primary biliary cirrhosis (PBC) is the presence of antimitochondrial antibodies. However, antinuclear antibodies (ANA) are also detectable in approximately 50% of subjects with PBC. Most clinical laboratories use indirect immunofluorescence microscopy to detect ANA and two labeling patterns that predominate in PBC are 'punctate nuclear rim' and 'multiple nuclear dots.' Work over the past several years has shown that antibodies giving these patterns most often recognize nuclear pore membrane protein gp210 and nuclear body protein sp100, respectively. These ANA are highly specific for PBC and detected in approximately 25% of patients. Less frequently, ANA apparently unique to PBC recognize other proteins of the nuclear envelope and nuclear bodies. While antibodies against gp210, sp100 and some other nuclear proteins are very specific to PBC and may therefore be useful diagnostic markers, their connection to pathogenesis remains to be elucidated.

Antigens, Nuclear↗
PubMed2003

Apoptosis induced by environmental stresses and amphotericin B in Candida albicans.

New antifungal agents are urgently required to combat life-threatening infections caused by opportunistic fungal pathogens like Candida albicans. The manipulation of endogenous fungal programmed cell death responses could provide a basis for future therapies. Here we assess the physiology of death in C. albicans in response to environmental stresses (acetic acid and hydrogen peroxide) and an antifungal agent (amphotericin B). Exposure of C. albicans to 40-60 mM acetic acid, 5-10 mM hydrogen peroxide, or 4-8 microg.ml-1 amphotericin B produced cellular changes reminiscent of mammalian apoptosis. Nonviable cells that excluded propidium iodide displayed the apoptotic marker phosphatidylserine (as shown by annexin-V-FITC labeling), were terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL)-positive (indicating nuclease-mediated double-strand DNA breakage), and produced reactive oxygen species. Ultrastructural changes in apoptotic cells included chromatin condensation and margination, separation of the nuclear envelope, and nuclear fragmentation. C. albicans cells treated at higher doses of these compounds showed cellular changes characteristic of necrosis. Necrotic cells displayed reduced TUNEL staining, a lack of surface phosphatidylserine, limited reactive oxygen species production, and an inability to exclude propidium iodide. Necrotic cells lacked defined nuclei and showed extensive intracellular vacuolization. Apoptosis in C. albicans was associated with an accumulation of cells in the G2/M phase of the cell cycle, and under some apoptosis-inducing conditions, significant proportions of yeast cells switched to hyphal growth before dying. This is a demonstration of apoptosis in a medically important fungal pathogen.

Acetic Acid↗
PubMed1977

Reversibly contractile nuclear matrix. Its isolation, structure, and composition.

From Tetrahymena macronuclei we have isolated a reversibly contractile nucleo-skeleton, i.e., an "expanded" nuclear matrix which reversibly contracts when the total concentration of the bivalent cations, Ca and Mg (3:2), is decreased to 5 mM or increased to 125 mM. During contraction the average diameter of the expanded matrix becomes reduced by about 24%; this corresponds to a volume contraction of about 55%. The reversible contraction of the nuclear matrix does not depend on ATP and cannot be inhibited by salygran. The expanded matrix is obtained by removing carefully from the macronuclei 89.7% of the phospholipid, 99.6% of the DNA, 98.5% of the RNA, and 74.8% of the protein by treatment with Triton X-100 and digestion with DNase and RNase followed by an extraction with 2 M NaCl. Electron microscopy reveals, within the expanded matrix, residual equivalents to the structures characteristic for macronuclei: (a) a residual nuclear envelope with nuclear pore complexes; (b) residual nucleoli at the periphery; (c) a fibrillar internal network. The expanded matrix is essentially composed of proteins (96.2%) and traces of DNA (0.8%), RNA (0.5%), phospholipid (1.6%), and carbohydrates (0.9%). The last, which have been determined by gas chromatography, contain glucose, mannose, and an unidentified sugar in the ratio 1:5.4:5.7. The ratio of acidic to basic amino acids of the expanded matrix is 1.55. Sodium dodecyl sulfate (SDS) gel electrophoresis reveals a predominant protein with a mol wt of 18,000 which is apparently involved in the reversible contractile process. The mechanism of this reversible contraction of the expanded matrix remains to be elucidated, but it differs both from actin-myosin contraction systems and from the contractile spasmoneme system in vorticellids.

Calcium↗
PubMed1978

Rat liver nuclear skeleton and ribonucleoprotein complexes containing HnRNA.

Rat liver nuclei deprived of chromatin and nucleoplasm show a spongelike network which preserves its connection with nucleoli, the inner membrane of the nuclear envelope, and nuclear pore complexes. It contains all of the HnRNA, provided the endogenous proteolytic activity is inhibited by a proteolytic inhibitor such as phenylmethyl sulfonyl chloride (PMSC) or the fluoride form (PMSF). In the absence of these proteolytic inhibitors, HnRNA is dissociated from the spongelike network and sediments in a sucrose gradient as polydispersed ribonucleoprotein complexes. Furthermore, purified HnRNA as well as rRNA do not bind to the spongelike network when added to these nuclei. These observations demonstrate that the association of HnRNA to the nuclear skeleton is not an artifact. RNase treatment of the spongelike network digests the majority of the rapidly labeled RNA but does not alter the morphological aspect nor the architecture of this network. EDTA and heparin treatments affect neither the attachment of HnRNA nor the structural organization of this network. Electron microscope studies of the network reveal a characteristic flexuous configuration. Its relationship with diffused and condensed chromatin is discussed.

Animals↗
PubMed2000

Association of prenylated proteins with the plasma membrane and the inner nuclear membrane is mediated by the same membrane-targeting motifs.

Targeting of nuclear lamins to the inner nuclear envelope membrane requires a nuclear localization signal and CaaX motif-dependent posttranslational modifications, including isoprenylation and carboxyl methylation. These modifications, although necessary for membrane targeting, are not sufficient to mediate stable association with membranes. We show that two variants of lamin B3 (i.e., B3a and B3b) exist in Xenopus oocytes. They are encoded by two alternatively spliced, developmentally regulated mRNAs. The two lamin variants differ greatly in their membrane association in meiotically matured eggs. The presence of an extra cysteine residue (as a potential palmitoylation site) and a basic cluster in conjunction with the CaaX motif function as secondary targeting signals responsible for the stable membrane association of lamin B3b in Xenopus eggs. Moreover, transfection experiments with Green Fluorescent Protein lamin tail chimeras and with a Green Fluorescent Protein N-Ras chimera show that these secondary motifs are sufficient to target proteins to the inner nuclear membrane and/or the plasma membrane. Implications for the intracellular trafficking of doubly lipidated proteins are discussed.

Amino Acid Sequence↗
PubMed2004

The entire Nup107-160 complex, including three new members, is targeted as one entity to kinetochores in mitosis.

In eukaryotes, bidirectional transport of macromolecules between the cytoplasm and the nucleus occurs through elaborate supramolecular structures embedded in the nuclear envelope, the nuclear pore complexes (NPCs). NPCs are composed of multiple copies of approximately 30 different proteins termed nucleoporins, of which several can be biochemically isolated as subcomplexes. One such building block of the NPC, termed the Nup107-160 complex in vertebrates, was so far demonstrated to be composed of six different nucleoporins. Here, we identify three WD (Trp-Asp)-repeat nucleoporins as new members of this complex, two of which, Nup37 and Nup43, are specific to higher eukaryotes. The third new member Seh1 is more loosely associated with the Nup107-160 complex biochemically, but its depletion by RNA interference leads to phenotypes similar to knock down of other constituents of this complex. By combining green fluorescent protein-tagged nucleoporins and specific antibodies, we show that all the constituents of this complex, including Nup37, Nup43, Seh1, and Sec13, are targeted to kinetochores from prophase to anaphase of mitosis. Together, our results indicate that the entire Nup107-160 complex, which comprises nearly one-third of the so-far identified nucleoporins, specifically localizes to kinetochores in mitosis.

Animals↗
PubMed2006

The Mcp element mediates stable long-range chromosome-chromosome interactions in Drosophila.

Chromosome organization inside the nucleus is not random but rather is determined by a variety of factors, including interactions between chromosomes and nuclear components such as the nuclear envelope or nuclear matrix. Such interactions may be critical for proper nuclear organization, chromosome partitioning during cell division, and gene regulation. An important, but poorly documented subset, includes interactions between specific chromosomal regions. Interactions of this type are thought to be involved in long-range promoter regulation by distant enhancers or locus control regions and may underlie phenomena such as transvection. Here, we used an in vivo microscopy assay based on Lac Repressor/operator recognition to show that Mcp, a polycomb response element from the Drosophila bithorax complex, is able to mediate physical interaction between remote chromosomal regions. These interactions are tissue specific, can take place between multiple Mcp elements, and seem to be stable once established. We speculate that this ability to interact may be part of the mechanism through which Mcp mediates its regulatory function in the bithorax complex.

ATP-Binding Cassette Transporters↗
PubMed2006

The nuclear GTPase Gsp1p can affect proper telomeric function through the Sir4 protein in Saccharomyces cerevisiae.

The small Ras-like GTPase Ran/Gsp1p is a highly conserved nuclear protein required for the nucleocytoplasmic trafficking of macromolecules. Recent findings suggest that the Ran/Gsp1p pathway may have additional roles in several aspects of nuclear structure and function, including spindle assembly, nuclear envelope formation, nuclear pore complex assembly and RNA processing. Here, we provide evidence that Gsp1p can regulate telomeric function in Saccharomyces cerevisiae. We show that overexpression of PRP20, encoding the Gsp1p GDP/GTP nuclear exchange factor, specifically weakens telomeric silencing without detectably affecting nucleocytoplasmic transport. In addition to this silencing defect, we show that Rap1p and Sir3p delocalize from their normal telomeric foci. Interestingly, Gsp1p was found to interact genetically and physically with the telomeric component Sir4p. Taken together, these results suggest that the GSP1 pathway could regulate proper telomeric function in yeast through Sir4p.

Chromatin Immunoprecipitation↗
PubMed1993

Role of nuclear pore complex in simian virus 40 nuclear targeting.

Cytoplasmically injected simian virus 40 (SV40) virions enter the nucleus through nuclear pore complexes (NPCs) and can express large T antigen shortly thereafter (J. Clever, M. Yamada, and H. Kasamatsu, Proc. Natl. Acad. Sci. USA 88:7333-7337, 1991). The nuclear import of the protein components of introduced SV40 was reversibly arrested by chilling and energy depletion, corroborating our previous observation that the nuclear entry of injected SV40 is blocked in the presence of wheat germ agglutinin and an antinucleoporin monoclonal antibody (mAb414), general inhibitors of NPC-mediated import. The nuclear accumulation of virion protein components and large T antigen in nonpermissive NIH 3T3 cells was similar to that in the permissive host, indicating that the ability to use NPCs as a route of nuclear entry appears to be a general property of the injected virus. Injected virions were capable of completing their lytic cycle and forming plaques in permissive cells. During the early phase of SV40 infection, the cytoplasmic injection of mAb414 effectively blocked nuclear T-antigen accumulation for up to 8 h of infection but had very little effect after 12 h of infection. The time-dependent interference with nuclear T-antigen accumulation by the antinucleoporin antibody is consistent with the hypothesis that the infecting virions enter the nucleus through NPCs. The interference study also suggests that the early phase of infection consists of at least two steps: a step for virion cell entry and intracytoplasmic trafficking and a step for virion nuclear entry followed by large-T-antigen gene expression and subsequent nuclear localization of the gene product. Virions were visualized as electron-dense particles in ultrathin sections of samples in which transport was permitted or arrested. In the former cells, electron-dense particles were predominantly observed in the nucleus. The virions were distributed randomly and nonuniformly in the nucleoplasm but were not observed in heterochromatin or in nucleoli. In the latter cells, the electron-dense particles were seen intersecting the nuclear envelope, near the inner nuclear membrane, and in NPCs. In tangential cross sections of NPCs, which appeared as donut-shaped structures, a spherical electron-dense particle was observed in the center of the structure. Immunoelectron microscopy revealed that NPCs were selectively decorated with 5-nm colloidal gold particles-anti-Vp1 immunoglobulin G at the cytoplasmic entrance to and in NPCs, confirming that the morphologically observed electron-dense particles in NPCs contain the viral structural protein. These results support the hypothesis that the nuclear import of SV40 is catalyzed through NPCs by an active transport mechanism that is similar to that of other karyophiles.

3T3 Cells↗
PubMedDate not supplied

Morphological changes and nuclear pore clustering during nuclear degradation in differentiating bovine lens fibre cells.

The programmed degradation of organelles is a characteristic feature of lens fibre cell differentiation. Due to the large number of similarities between the programmed organelle loss during lens development and the changes to organelles in apoptosis, lens cell differentiation has been suggested to share a common basis with programmed cell death. This study was aimed at characterising the morphological changes to the nucleus during cellular differentiation in the bovine lens at the ultrastructural level. Progressive shrinkage of the nucleus is accompanied by clumping and marginalisation of the chromatin to the nuclear periphery. Additionally, the fate of another key component of the nuclear envelope--the nuclear pore complexes--was followed. In parallel to the shrinkage of the nucleus, the nuclear pores progressively cluster into large aggregates that associate with the condensed DNA. These observations in differentiating lens fibres mirror the situation in cells undergoing apoptosis and thus provide additional data supporting a common basis between the two processes.

Animals↗