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PubMed2000

Novel biochemical and functional insights into nuclear Ca(2+) transport through IP(3)Rs and RyRs in osteoblasts.

We report the first biochemical and functional characterization of inositol trisphosphate receptors (IP(3)Rs) and ryanodine receptors (RyRs) in the nuclear membrane of bone-forming (MC3T3-E1) osteoblasts. Intact nuclei fluoresced intensely with anti-RyR (Ab(34)) and anti-IP(3)R (Ab(40)) antisera in a typically peripheral nuclear membrane pattern. Isolated nuclear membranes were next subjected to SDS-PAGE and blotted with isoform-specific anti-receptor antisera, notably Ab(40), anti-RyR-1, anti-RyR-2 (Ab(129)), and anti-RyR-3 (Ab(180)). Only anti-RyR-1 and Ab(40) showed bands corresponding, respectively, to full-length RyR-1 ( approximately 500 kDa) and IP(3)R-1 (approximately 250 kDa). Band intensity was reduced by just approximately 20% after brief tryptic proteolysis of intact nuclei; this confirmed that isolated nuclear membranes were mostly free of endoplasmic reticular contaminants. Finally, the nucleoplasmic Ca(2+) concentration ([Ca(2+)](np)) was measured in single nuclei by using fura-dextran. The nuclear envelope was initially loaded with Ca(2+) via Ca(2+)-ATPase activation (1 mM ATP and approximately 100 nM Ca(2+)). Adequate Ca(2+) loading was next confirmed by imaging the nuclear envelope (and nucleoplasm). Exposure of Ca(2+)-loaded nuclei to IP(3) or cADP ribose resulted in a rapid and sustained [Ca(2+)](np) elevation. Taken together, the results provide complementary evidence for nucleoplasmic Ca(2+) influx in osteoblasts through nuclear membrane-resident IP(3)Rs and RyRs. Our findings may conceivably explain the direct regulation of osteoblastic gene expression by hormones that use the IP(3)-Ca(2+) pathway.

3T3 Cells↗
PubMed1993

Physical mapping of buzura suppressaria nuclear polyhedrosis virus genome.

A physical map of the genome of buzura suppressaria singly-enveloped nuclear polyhedrosis virus (BsSNPV) was determined using six restriction endonucleases (RE), singly or in pairs, and Southern hybridizations of cloned or gel-purified DNA fragments. The maps of the genomes of BsSNPV and autographa californica multiply-enveloped nuclear polyhedrosis virus (AcMNPV) were different.

Animals↗
PubMed2002

Internalized group V secretory phospholipase A2 acts on the perinuclear membranes.

Mammalian secretory phospholipases A(2) (sPLA(2)) have been implicated in cellular eicosanoid biosynthesis but the mechanism of their cellular action remains unknown. To elucidate the spatiotemporal dynamics of sPLA(2) mobilization and determine the site of its lipolytic action, we performed time-lapse confocal microscopic imaging of fluorescently labeled sPLA(2) acting on human embryonic kidney (HEK) 293 cells the membranes of which are labeled with a fluorogenic phospholipid, N-((6-(2,4-dinitrophenyl)amino)hexanoyl)-1-hexadecanoyl-2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-sn-glycero-3-phosphoethanolamine. The Western blotting analysis of HEK293 cells treated with exogenous sPLA(2)s showed that not only the affinity for heparan sulfate proteoglycan but also other factors, such as sPLA(2) hydrolysis products or cytokines, are necessary for the internalization of sPLA(2) into HEK293 cells. Live cell imaging showed that the hydrolysis of fluorogenic phospholipids incorporated into HEK293 cell membranes was synchronized with the spatiotemporal dynamics of sPLA(2) internalization, detectable initially at the plasma membrane and then at the perinuclear region. Also, immunocytostaining showed that human group V sPLA(2) induced the translocation of 5-lipoxygenase to the nuclear envelope at which they were co-localized. Together, these studies provide the first experimental evidence that the internalized sPLA(2) acts on the nuclear envelope to provide arachidonate for other enzymes involved in the eicosanoid biosynthesis.

Arachidonate 5-Lipoxygenase↗
PubMed2007

Localization of proteasomes and proteasomal proteolysis in the mammalian interphase cell nucleus by systematic application of immunocytochemistry.

Proteasomes are ATP-driven, multisubunit proteolytic machines that degrade endogenous proteins into peptides and play a crucial role in cellular events such as the cell cycle, signal transduction, maintenance of proper protein folding and gene expression. Recent evidence indicates that the ubiquitin-proteasome system is an active component of the cell nucleus. A characteristic feature of the nucleus is its organization into distinct domains that have a unique composition of macromolecules and dynamically form as a response to the requirements of nuclear function. Here, we show by systematic application of different immunocytochemical procedures and comparison with signature proteins of nuclear domains that during interphase endogenous proteasomes are localized diffusely throughout the nucleoplasm, in speckles, in nuclear bodies, and in nucleoplasmic foci. Proteasomes do not occur in the nuclear envelope region or the nucleolus, unless nucleoplasmic invaginations expand into this nuclear body. Confirmedly, proteasomal proteolysis is detected in nucleoplasmic foci, but is absent from the nuclear envelope or nucleolus. The results underpin the idea that the ubiquitin-proteasome system is not only located, but also proteolytically active in distinct nuclear domains and thus may be directly involved in gene expression, and nuclear quality control.

Acetylcysteine↗
PubMed1991

[Systemic reorganization of the architechtonics of polytene chromosomes in onto- and phylogenesis of malaria mosquitoes. Structural features regional of chromosomal adhesion to the nuclear membrane].

Principles of organization of chromocenter in salivary gland cells and zones of chromosome attachment to nuclear envelope in ovarian nurse cells were determined. It was shown that blocks of centromeric heterochromatin (alfa-heterochromatin) have no direct connection with nuclear envelope. Such connections are ensured by beta-heterochromatin. Homologous chromosome regions were shown to be of different morphology and nature of chromosome-membrane links in different mosquito species. A map of polytene chromosomes of ovarian nurse cells in Anopheles messeae Fall, was established. No differences were found in band quantity of these chromosomes as compared to salivary gland chromosomes.

Animals↗
PubMed1991

Localization of a myosin heavy chain-like polypeptide to Drosophila nuclear pore complexes.

Antibodies previously used for immunofluorescence localization of a myosin heavy chain-like polypeptide to the nuclear envelope in higher eukaryotic cells crossreact with both muscle and nonmuscle isoforms of Drosophila myosin heavy chain. Analyses of Drosophila tissue culture cells and premyogenic embryos suggest that it is the nonmuscle isoform that is associated with the nuclear envelope. Further immunofluorescence and immunoelectron microscopy indicate that this polypeptide is associated with nuclear pore complexes. These data support the hypothesis put forward previously that myosin or myosin-like molecules play a role in pore complex architecture.

Animals↗
PubMed1992

A 62-kD protein required for mitotic progression is associated with the mitotic apparatus during M-phase and with the nucleus during interphase.

A protein of 62 kD is a substrate of a calcium/calmodulin-dependent protein kinase, and both proteins copurify with isolated mitotic apparatuses (Dinsmore, J. H., and R. D. Sloboda. 1988. Cell. 53:769-780). Phosphorylation of the 62-kD protein increases after fertilization; maximum incorporation of phosphate occurs during late metaphase and anaphase and correlates directly with microtubule disassembly as determined by in vitro experiments with isolated mitotic apparatuses. Because 62-kD protein phosphorylation occurs in a pattern similar to the accumulation of the mitotic cyclin proteins, experiments were performed to determine the relationship between cyclin and the 62-kD protein. Continuous labeling of marine embryos with [35S]methionine, as well as immunoblots of marine embryo proteins using specific antibodies, were used to identify both cyclin and the 62-kD protein. These results clearly demonstrate that the 62-kD protein is distinct from cyclin and, unlike cyclin, is a constant member of the cellular protein pool during the first two cell cycles in sea urchin and surf clam embryos. Similar results were obtained using immunofluorescence microscopy of intact eggs and embryos. In addition, immunogold electron microscopy reveals that the 62-kD protein associates with the microtubules of the mitotic apparatus in dividing cells. Interestingly, the protein changes its subcellular distribution with respect to microtubules during the cell cycle. Specifically, during mitosis the 62-kD protein associates with the mitotic apparatus; before nuclear envelope breakdown, however, the 62-kD protein is confined to the nucleus. After anaphase, the 62-kD protein returns to the nucleus, where it resides until nuclear envelope disassembly of the next cell cycle.

Animals↗
PubMed2002

Tpr is localized within the nuclear basket of the pore complex and has a role in nuclear protein export.

Tpr is a coiled-coil protein found near the nucleoplasmic side of the pore complex. Since neither the precise localization of Tpr nor its functions are well defined, we generated antibodies to three regions of Tpr to clarify these issues. Using light and EM immunolocalization, we determined that mammalian Tpr is concentrated within the nuclear basket of the pore complex in a distribution similar to Nup153 and Nup98. Antibody localization together with imaging of GFP-Tpr in living cells revealed that Tpr is in discrete foci inside the nucleus similar to several other nucleoporins but is not present in intranuclear filamentous networks (Zimowska et al., 1997) or in long filaments extending from the pore complex (Cordes et al., 1997) as proposed. Injection of anti-Tpr antibodies into mitotic cells resulted in depletion of Tpr from the nuclear envelope without loss of other pore complex basket proteins. Whereas nuclear import mediated by a basic amino acid signal was unaffected, nuclear export mediated by a leucine-rich signal was retarded significantly. Nuclear injection of anti-Tpr antibodies in interphase cells similarly yielded inhibition of protein export but not import. These results indicate that Tpr is a nucleoporin of the nuclear basket with a role in nuclear protein export.

Active Transport, Cell Nucleus↗
PubMed1994

Ultrastructural distribution of calcium in the rat testis.

Despite the important role of calcium in the growth and differentiation of a variety of cell types, its exact location and function in the somatic and germ cells of the testis remain to be determined. In the present study, we examined the subcellular distribution of calcium in the immature and adult rat testis. Calcium was localized at the electron microscopic level by ion-capture cytochemistry using combined oxalate and pyroantimonate procedures. Calcium-containing precipitates localized primarily within the nuclei, mitochondria, and cytosol of somatic and germ cells. Differences in the size and quantity of the calcium precipitates were observed among the various cellular compartments. In the somatic cells (Sertoli, Leydig, and myoid), the nuclei exhibited large round-shaped calcium-containing precipitates, whereas the mitochondria in these cell types contained numerous smaller precipitates. The cytoplasmic vesicles possessed single precipitates. These vesicles could be calciosomes, which have been described in other non-muscle cell types. Among germ cells, round spermatids exhibited a large number of vesicular, calsiosome-like structures in the cytoplasm containing single precipitates. The elongating spermatids from adult testis showed calcium localization within the nuclear matrix unassociated with the nuclear envelope, or in a peripheral alignment of precipitates along the nuclear envelope. Calciosome-like structures were also seen in round spermatids. Spermatogonia and spermatocytes exhibited calcium in nuclei, mitochondria, and cytoplasmic vesicles. These results demonstrate a differential distribution of calcium within the various cell types of the testis. The presence of calcium in the nucleus may suggest a role in cell growth and differentiation; calsiosome-like structures may represent the active exchangeable pool of calcium, and the differential type of distribution of calcium in elongating spermatids suggests a role for calcium in spermatid differentiation.

Animals↗
PubMed1980

Cytochemical studies on the relation of nucleoside triphosphatase activity to ribonucleoproteins in isolated rat liver nuclei.

Cytochemical tests for nucleosidetriphosphatase (NTPase) and Bernhard's preferential staining for ribonucleoproteins (RNP) were applied to isolated rat liver nuclei. The strongest and most easily reproducible positive reaction for NTPase was detected at pH 7.7 with ATP and GTP. This reaction was activated by Mg2+ and Ca2+ and inhibited by Be2+, Zn2+, quercetin, and ribonuclease. The major sites of enzyme reaction were intranuclear RNA-containing structures. Incubation of nuclei in ATP-stimulated RNA-release medium eliminated a considerable part of the material showing both NTPase reaction and staining for RNP; the perichromatin granules disappeared, while interchromatin granules remained. NTPase activity in the nuclear envelope seems to be associated with the annular part of nuclear pore complexes (permanent component) and with RNP particles translocated through nuclear pores or attached to the surface of nuclei (transitional component). From a morphological point of view, these observations support previous biochemical data suggesting the existence of a connection between NTPase activity and the translocation of RNP particles through the nuclear envelope.

Adenosine Triphosphatases↗
PubMed1978

The fine structure of fertilization in the fern Marsilea vestita.

The ultrastructural details of fertilization in the fern Marsilea vestita, including gamete approach and fusion, the fate of the spermatozoid organelles and the development of a possible block to polyspermy are described. The spermatozoid approaches the egg through layers of mucilage that surround the megaspores. It moves down the neck of the archegonium into the cavity above the egg. In order to reach the egg, it must move through a small hole in the thick wall that lies across the top of the egg. The fusion of the plasma membranes of the gametes results in an outflow of egg cytoplasm into the clear space under the sperm plasma membrane, creating a fertilization cone. All the organelles of the fertilizing spermatozoid, including nucleus, mitochondrion, microtubule ribbon, multilayered structure, and flagellar band, with approximately 150 flagella, enter the egg cytoplasm. The nucleus enters as a condensed rod of chromatin with no nuclear envelope. The chromatin begins to disperse immediately and a new nuclear envelope is formed around the chromatin by egg endoplasmic reticulum. The mitochondrion and the microtubules of the ribbon and flagella are broken down, but the fates of the flagellar band and the multilayered structure have not been determined. After spermatozoid penetration, a new extracellular layer appears above the surface of the egg, beginning in the region of sperm penetration and spreading across the top of the egg. This layer may be important in preventing other spermatozoids from fusing with the egg.

Cell Fusion↗
PubMed1976

Binding of metabolically activated benzo(a)pyrene to nuclear macromolecules.

The binding of metabolically activated [3H]benzo(a)pyrene ([3H]BP) to the DNA, RNA, histones, and nonhistones of isolated rat liver and lung nuclei was studied. Conditions for optimal binding to the nuclear components were determined. Upon incubation with isolated liver nuclei and reduced nicotinamide adenine dinucleotide phosphate, [3H]BP was able to bind to nuclear components. The binding appeared to be covalent in nature. Treatment of the rats with 3-methylcholanthrene induced the nuclear aryl hydrocarbon hydroxylase (AHH) activity and also increased the level of carcinogen binding. The addition of rat liver microsomes to the incubation systems greatly enhanced the level of [3H]BP binding to the macromolecules in the nuclei from both the control and 3-methylcholanthrene-treated rats, and the maximal levels of binding obtained with these two types of nuclei were similar. The binding was inhibited by 7,8-benzoflavone or glutathione. Lung nuclei from control rats had very low AHH activity and did not exhibit appreciable carcinogen binding, whereas those from 3-methylcholanthrene-pretreated animals had slightly higher AHH activity and caused low levels of binding. The binding of [3H]BP to lung nuclei was greatly enhanced by liver microsomes but only slightly by lung microsomes, which had rather low AHH activity. Several lines of evidence indicate that, in the control experiments (no reduced nicotinamide adenine dinucleotide phosphate added), the radioactivity associated with the macromolecule fractions is probably a background value rather than due to the binding caused by a specific interaction between benzo(a)pyrene and cytochrome P-450. The present study clearly demonstrates that a carcinogen activated at the microsomes can enter into the nucleus and react with its macromolecules; the carcinogen can also be activated by the monoxygenase system of the nuclear envelope. It appears that both the endoplasmic reticulum and the nuclear envelope are potentially important sites of carcinogen activation.

Animals↗
PubMed1975

Ultrastructure of pulmonary macrophagic system.

A mature AMF, ready for phagocytosis, is a relatively large cell with an oval nucleus, with indentations of a nuclear envelope of varying depth. Evenly distributed chromatin forms beneath the nuclear envelope a rim of heterochromatin. There is a prominent nucleus with a distinct nucleolonemma. The cytoplasm is differentiated into a continuous ectoplasmic zone with numberous finger-like processes and pseudopodia. The organelles are formed by scattered round or oval mitochondria, a description is given of the Golgi apparatus in the juxtanuclear position, in certain sites multifocal in form, of the centriolar apparatus, scarce profiles of endoplasmic granular reticulum, dispersed free polyribosomes and microfilaments in varying amounts. The most outstanding feature is the rich lysosomal apparatus of varying structure depending on the functional state. Dynamics of the maturation of AMF was studied in intermediate phases, described here. The peribronchovascular connective tissue is the seat of free macrophages of a structure analogous with that of AMF. Fixed macrophages are anchored in the loose connective tissue by processes of different shape and length. The prevailing component of the cytoplasm are numerous vesicular structures and vacuoles as well as a marked lysosomal apparatus. Fixed macrophages phagocytize foreign material in situ. The septal cell exists in normal state as an element with numerous intricated processes pervading the fibrillar substrate. Numerous free polyribosomes and vacuoles are its most marked component. Activation of septal cells was demonstrated under experimental conditions. Their transformation into free macrophages is probable. In the pulmonary intersitium, in the perivascular loose connective tissue particularly free cells of a similar structure as blood monocytes were shown in normal state. Under experimental conditions an increased number of monocytes is present in pulmonary capillaries, e.g. 24 hours after an intratracheal instillation of India ink colloid solution. At the same interval a number of free cells of the monocyte structure was found in the perivascular connective tissue and also in the alveolar lumen, with phagocytized carbon. An increased number of monocytes transforming into macrophagic cells was visualized in this localization as late as 14 days after the instillation of India ink colloid solution. The experimental study with an intratracheal instillation of India ink colloid solution in the mouse gave evidence of a high readiness of AMF. The carbon particles were seen phagocytized at an interval of 5 minutes after instillation. In all intervals during which free carbon particles were present in the alveolar epithelium mature AMF were observed with no or very low phagocytic activity, their lysosomal apparatus being prominent. On the contrary, in the phagocytizing AMF, the lysosomal apparatus disappeared in the greatest part of the cytoplasm. The clearance of AMF occurs predominantly by the air route...

Animals↗
PubMed1987

Centrosome-kinetochore interaction in multinucleate cells.

The interaction between centrosomes and kinetochores was studied in multinucleate cells induced by Colcemid treatment or by random cell fusion. Except for prematurely condensed chromosomes (PCC) of the G2-phase, PCCs do not develop their own spindle area. Perhaps the maturation promoting factor (MPF) fails to activate these centrosomes. In such PCCs, the kinetochore-centrosome interaction was found to be non-specific: sometimes only a few chromosomes of a group could establish connections with centrosomes, sometimes chromosomes from the same PCC group developed microtubule (MT) attachment with different centrosomes (not the pair), and sometimes kinetochores of PCC groups failed to interact with MTs. These findings explain the abnormal mitotic behaviour of PCCs as seen in the light microscope. These PCCs develop micronuclei or normal nuclei by nuclear re-formation in telophase. All the different PCC groups revealed kinetochores with kinetochore plates. It was shown that transformation of presumptive kinetochores to a trilaminar kinetochore does not depend on nuclear envelope breakdown or on the degree of chromosome condensation. This may be induced by the MPF which may initiate different events like chromosome condensation, nuclear envelope breakdown and kinetochore transformation by secondary factors. Other observations like establishment of connections by different chromosome groups to a common centrosome, kinetochore attachment of PCCs to different centrosomes, interaction of one kinetochore with two centrosomes, kinetochores being stretched and bent to receive microtubules and finally the failure of some kinetochores to develop MT attachment, all strongly suggest that the kinetochores serve as the point of termination rather than the nucleation sites of kinetochore MTs.

Animals↗
PubMed2003

Loss of lamin A/C expression revealed by immuno-electron microscopy in dilated cardiomyopathy with atrioventricular block caused by LMNA gene defects.

Mutations of the LMNA gene encoding the lamin A and C nuclear envelope proteins cause an autosomal dominant form of dilated cardiomyopathy (DCM) with atrioventricular block (AVB). The aim of this study was to investigate ultrastructural nuclear membrane changes by conventional electron microscopy and protein expression by immuno-electron microscopy in the heart of patients with DCM and AVB due to LMNA gene mutations. Four immunohistochemical techniques were used: pre-embedding and post-embedding in Epon-Araldite resin and London Resin White (LRW), with and without silver enhancement. Parallel light microscopy immunohistochemistry studies were performed. Conventional electron microscopy showed a loss of integrity of the myocyte nuclei with blebs of the nuclear membrane, herniations and delamination of the nuclear lamina and nuclear pore clustering. Post-embedding LRW was the most informative technique for morphology and immuno-labelling. Immuno-labelling was almost absent in the nuclear envelope of patients with LMNA gene mutations, but intensely present in controls. The loss of labelling selectively affected myocyte nuclei; the endothelial cell nuclei were immunostained in patients and controls. Light immunohistochemistry confirmed the results. These findings confirm the hypothesis that LMNA gene defects are associated with a loss of protein expression in the selective compartment of non-cycling myocyte nuclei.

Adult↗
PubMed2002

Caspase processing and nuclear export of CTP:phosphocholine cytidylyltransferase alpha during farnesol-induced apoptosis.

CTP:phosphocholine cytidylyltransferase alpha (CCT alpha) is a nuclear enzyme that catalyzes the rate-limiting step in the CDP-choline pathway, the primary route for synthesis of phosphatidylcholine (PtdCho) in eukaryotic cells. Induction of apoptosis by farnesol (FOH) and other cytotoxic drugs has been shown to alter PtdCho synthesis via the CDP-choline pathway. Here we report that FOH-induced apoptosis in CHO cells caused a dose-dependent activation of CCT alpha and inhibition of the final step in the pathway, resulting in a biphasic effect on PtdCho synthesis. Activation of CCT alpha was accompanied by enzyme translocation to the nuclear envelope within 30 min of FOH addition to cells. Following translocation to membranes, CCT alpha was exported from the nucleus and underwent caspase-mediated proteolysis that coincided with poly(ADP-ribose) polymerase cleavage. Site-directed mutagenesis and in vivo and in vitro expression studies mapped a caspase 6 and/or 8 cleavage site to TEED(28 downward arrow)G, the final residue in the CCT alpha nuclear localization signal. Nuclear export of CCT alpha appeared to be an active process in FOH-treated CHO cells that was independent of caspase removal of the nuclear localization signal. Caspase cleavage of CCT alpha occurred during UV or chelerythrine-induced apoptosis; however, nuclear membrane translocation and nuclear export were not evident under these conditions. Thus, caspase cleavage of CCT alpha was a late feature of several apoptotic programs that occurred in the nucleus or at the nuclear envelope. Activation and nuclear export of CCT alpha were early events in FOH-induced apoptosis that contributed to altered PtdCho synthesis and, in conjunction with caspase cleavage, excluded CCT alpha from the nucleus.

3T3 Cells↗
PubMed1993

Identification of a nucleo-cytoplasmic ionic pathway by osmotic shock in isolated mouse liver nuclei.

The observation that the nuclear envelope outer membrane contains ion channels raises the question of whether these conductances communicate between the cytosol and the nuclear envelope cisternae or between the cytosol and the cytoplasm. Failure to detect large, nonselective holes using the patch-clamp technique has led to the speculation that ion channels and nuclear pores are in fact the same. In this paper we present evidence that the ionic channel, recorded in isolated liver nuclei with the patch-clamp configuration of "nucleus-attached," spans the double membrane of the envelope, providing a direct contact between nucleoplasm and cytoplasm.

Animals↗
PubMed2004

DNase I and fragmented chromatin during nuclear degradation in adult bovine lens fibers.

PURPOSE: Nuclear loss is a most remarkable organelle disappearance during terminal differentiation of lens fiber cells given that it implicates the full degradation of a major molecular component, DNA. Consequently, to gain insight into the progression of DNA cleavage we analyzed the appearance of single strand breaks in relationship with chromatin condensation. To assess a possible involvement of DNase I in DNA fragmentation we explored its localization in lens fibers having different degrees of nuclear breakdown, evaluated by the state of chromatin, nuclear envelope, and DNA. METHODS: Whole mounts of adult bovine lens epithelium as well as lens cryosections were utilized to examine, using antibodies or specific molecular probes, the localization of DNase I, nuclear membrane, lamins, and DNA 3'-OH-free termini. Nuclease activity gel and western blot assays were used to characterize DNase I in different lens fiber extracts. RESULTS: Nuclear morphology was found to undergo significant changes from the onset of fiber differentiation. Initial spherical nuclei present at early fibergenesis stages evolve to elongated ones in mature fibers. Chromatin did not present signs of condensation in these nuclei. However, nuclei from fibers located deeper in lens volume exhibited some chromatin condensation and fragmentation while the nuclear lamina appeared undamaged. At more advanced stages, different patterns of nuclear envelope integrity and chromatin condensation and cleavage were observed. DNase I was found in the cytoplasm in the very initial fibers and then in the nuclear territory. DNase I appeared closely associated with fully condensed and fragmented chromatin at the final phases of nuclear breakdown. CONCLUSIONS: DNase I is a nuclease present in bovine lens fibers and can be considered as an enzyme producing final DNA cleavage since it is closely associated with highly fragmented DNA in disintegrating nuclei.

Animals↗