Isolation and characterization of nuclei from bird erythrocytes

Detection and estimating the blood accumulation volume of brain hemorrhage in a human anatomical skull using a RF single coil

OBJECTIVE

An experimental study for testing a simple robust algorithm on data derived from an electromagnetic radiation device that can detect small changes in the tissue/fluid ratio in a realistic head configuration.

METHODS

Changes in the scattering parameters (S21) of an inductive coil resulting from injections of chicken blood in the 0-18 ml range into calf brain tissue in a human anatomical skull were measured over a 100-1,000 MHz frequency range.

RESULTS

An algorithm that combines amplitude and phase results was found to detect changes in the tissue/fluid ratio with 90% accuracy. An algorithm that estimated the injected blood volume was found to have a 1-4 ml average error. This demonstrates the possibility of the inductive coil-based device to possess a practical ability to detect a change in the tissue/fluid ratio in the head.

SIGNIFICANCE

This study is an important step towards the goal of building an inexpensive and safe device that can detect an early brain hemorrhagic stroke.

The importance of hydration and DNA conformation in interpreting infrared spectra of cells and tissues

Since Watson and Crick's historical papers on the structure and function of DNA based on Rosalind Franklin's and Maurice Wilkin's X-ray diffraction patterns tremendous scientific curiosity has been aroused by the unique and dynamic structure of the molecule of life. A-DNA and B-DNA represent different conformations of the DNA molecule, which is stabilised by hydrogen interactions between base pairs, stacking interactions between neighboring bases and long-range intra- and inter-backbone forces. This review highlights the contribution Fourier transform infrared (FTIR) spectroscopy has made to the understanding of DNA conformation in relation to hydration and its potential role in clinical diagnostics. The review will first begin by elucidating the main forms of DNA conformation found in nature and the general structures of the A, B and Z forms. This is followed by a detailed critique on infrared spectroscopy applied to DNA conformation highlighting pivotal studies on isolated DNA, polynucleotides, nucleoprotein and nucleohistone complexes. A discussion on the potential of diagnosing cancer using FTIR spectroscopy based on the detection of DNA bands in cells and tissues will ensue, highlighting the recent studies investigating the conformation of DNA in hydrated and dehydrated cells. The method of hydration as a way to facilitate DNA conformational band assignment will be discussed and the conformational change to the A-form upon dehydration will be used to explain the reason for the apparent lack of FTIR DNA signals observed in fixed or air-dried cells and tissues. The advantages of investigating B-DNA in the hydrated state, as opposed to A-DNA in the dehydrated state, are exemplified in a series of studies that show: (1) improved quantification of DNA in cells; (2) improved discrimination and reproducibility of FTIR spectra recorded of cells progressing through the cell cycle; (3) insights into the biological significance of A-DNA as evidenced by an interesting study on bacteria, which can survive desiccation and at the same time undergo the B-A-B transition. Finally, the importance of preserving the B-DNA conformation for the diagnosis of cancer is put forward as way to improve the sensitivity of this powerful technique.

Quantification of DNA in simple eukaryotic cells using Fourier transform infrared spectroscopy

A technique capable of detecting and monitoring nucleic acid concentration offers potential in diagnosing cancer and further developing an understanding of the biochemistry of disease. The application of Fourier transform infrared (FTIR) spectroscopy has previously been hindered by the supposed non-Beer-Lambert absorption behavior of DNA in intact cells making elucidation of the DNA bands difficult. We use known composition DNA/hemoglobin standards to successfully estimate the DNA content in avian erythrocyte nuclei (44.2%) and intact erythrocytes (12.8%). Furthermore we demonstrate that the absorption of cellular DNA does follow the Beer-Lambert Law and highlights the role of conformation and hydration in FTIR spectroscopy of biological samples.

Monitoring the reversible B to A-like transition of DNA in eukaryotic cells using Fourier transform infrared spectroscopy

The ability to detect DNA conformation in eukaryotic cells is of paramount importance in understanding how some cells retain functionality in response to environmental stress. It is anticipated that the B to A transition might play a role in resistance to DNA damage such as heat, desiccation and toxic damage. To this end, conformational detail about the molecular structure of DNA has been derived primarily from in vitro experiments on extracted or synthetic DNA. Here, we report that a B- to A-like DNA conformational change can occur in the nuclei of intact cells in response to dehydration. This transition is reversible upon rehydration in air-dried cells. By systematically monitoring the dehydration and rehydration of single and double-stranded DNA, RNA, extracted nuclei and three types of eukaryotic cells including chicken erythrocytes, mammalian lymphocytes and cancerous rodent fibroblasts using Fourier transform infrared (FTIR) spectroscopy, we unequivocally assign the important DNA conformation marker bands within these cells. We also demonstrate that by applying FTIR spectroscopy to hydrated samples, the DNA bands become sharper and more intense. This is anticipated to provide a methodology enabling differentiation of cancerous from non-cancerous cells based on the increased DNA content inherent to dysplastic and neoplastic tissue.

A novel nonhistone protein (MENT) promotes nuclear collapse at the terminal stage of avian erythropoiesis

The terminal stage of differentiation of nucleated chicken erythrocytes is associated with an overall gene repression and a condensation of the repressed chromatin portion. Two-dimensional DNP electrophoresis has been used to separate transcriptionally active and repressed chromatin of mature chicken erythrocytes. The repressed chromatin fraction is shown to be enriched with histone H5 as well as with a 42-kDa nonhistone chromosomal protein. The 42-kDa protein designated here as MENT (mature erythrocyte nuclear termination stage-specific protein) is hyperexpressed at the terminal stage of chicken erythropoiesis and is accumulated in adult chicken erythrocyte nuclei. This protein was purified by ion-exchange chromatography from 0.4 M NaCl extracts of the erythrocyte nuclei. It appeared to be a basic polypeptide (pI 9.2) which, however, precipitated at low pH. When reconstituted in vitro with immature erythrocyte nuclei, MENT promoted condensation of intact nuclear chromatin and enhanced the solubilization of nuclease-digested polynucleosomes, thus mimicking the processes occurring in vivo at the final stage of erythrocyte maturation. The extent of dissociation of specific gene sequences from the nuclear matrix in MENT-treated nuclei is in striking correlation with their transcriptional activity. No other basic proteins (H5, cytochrome c, RNase A) added to the nuclear preparation at the same level as MENT (protein/DNA = 0.005) caused any effect on nuclear organization. No alterations were observed when MENT was mixed with erythroblasts and nonerythroid nuclei having little or no histone H5. We propose that MENT cooperates with histone H5 to complete the nuclear collapse in mature nucleated erythrocytes.

A mixing chamber to enucleate avian and fish erythrocytes: preparation of their plasma membrane

Biochemical studies of the plasma membrane and the cytoskeleton of nucleated erythrocytes are strongly limited by the difficulties encountered in enucleating large quantities of cells. We describe an easily built hydrodynamic system which allows rapid preparation of large amounts of avian and fish erythrocyte plasma membranes. The contents of two 25-ml syringes containing hemolyzed nucleated erythrocytes are forced through four capillaries to a specially designed mixing chamber which fills a collecting syringe. The 50-ml erythrocyte suspension can be processed in 2 s. The high speed flow is achieved with a hand-activated piston. The turbulences in the mixing chamber are carried to an optimal efficiency by the vis-à-vis disposition of the four mixing jets. The enucleated membranes are separated from the nuclei and residual nucleated cells by differential centrifugations. They do not show contamination with nuclear material. Erythrocytes from chicken and trout have been used. They present striking differences in their stability toward hydrodynamic disruption, erythrocytes from chicken being far more stable. Ninety-five percent of trout erythrocytes are enucleated after only one run through the mixing chamber. Two runs performed at the maximal flow rate are necessary to enucleate chicken erythrocytes with a yield of 80%. In the former case most of the purified enucleated plasma membranes are fragmented in small vesicles while they retain a large size in the case of chicken erythrocytes. The proteins of the membranes thus prepared are characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis: we found that erythrocyte membranes from trout are remarkable for their small spectrin content compared to those from chicken.

Status of the nuclear matrix in mature and embryonic chick erythrocyte nuclei

The adult chicken erythrocyte nucleus was found to lack an internal nuclear matrix: even milder extraction procedures resulted in the production of empty shells of pore complex-lamina together with loose aggregates of core histone. In contrast, rat liver nuclei showed a typical intranuclear salt-resistant skeleton. These results show that an internal matrix is not an obligatory nuclear component, and is not required for the spatial organization of chromatin. 5-day-old embryonic erythrocytes did, however, contain an interchromatinic nuclear matrix, suggesting a correlation between the presence of matrix structures, and nuclear 'activity'.

Synemin and vimentin are components of intermediate filaments in avian erythrocytes

Synemin, a high-molecular-weight protein associated with intermediate filaments in muscle, and vimentin, an intermediate-filament subunit found in many different cell types, have been identified by immunologic and electrophoretic criteria as components of intermediate filaments in mature avian erythrocytes. Desmin, the predominant subunit of intermediate filaments in muscle, has not been detected in these cells. Two dimensional immunoautoradiography of proteolytic fragments of synemin and vimentin demonstates that the erythrocyte proteins are highly homologous, if not identical, to their muscle counterparts. Double immunoflurorescence reaveals that erythrocyte synemin and vimentin co-localize in a cytoplasmic network of sinuous filaments that extends from the nucleus to the plasma membrane and resists aggregation by colcemid. Erythrocytes that are attached to glass cover slips can be sonicated to remove nuclei and nonadherent regions of the plasma membrane; this leaves elliptical patches of adherent membrane that retain mats of vimentin- and synemin-containing intermediate filaments, as seen by immunofluorescence and rotary shadowing. Similarly, mechanical enucleation of erythrocyte ghosts in suspension allows isolation of plasma membranes that retain a significant fraction of the synemin and vimentin, as assayed by electrophoresis, and intermediate filaments, as seen in thin sections. Both synemin and vimentin remain insoluble along with spectrin and actin, in solutions containing nonionic detergent and high salt. However, brief exposure of isolated membrane to distilled water releases the synemin and vimentin together in nearly pure form, before the release of significant amounts of spectrin and actin. These data suggest that avian erythrocyte intermeditate filaments are somehow anchored to the plasma membrane; erythrocytes may thus provide a simple system for the study of intermediate filaments and their mode of interaction with membranes. In addition, these data, in conjunction with previous data from muscle, indicate that synemin is capable of associating with either desmin or vimentin and may thus perform a special role in the structure or function of intermediate filaments in erythrocytes as well as muscle.

Chromatin substructure: an electron microscopic study of thin-sectioned chromatin subjected to sequential protein extraction and water swelling procedures

Electron microscopic observations and measurements were made on thin-sectioned chromatin fibers and fibrils obtained from nuclei of mature chicken erythrocytes. The nuclei were isolated in low ionic strength gum arabic and octanol then extracted sequentially with (1) 0.14 M NaCl, (2) 0.25 N HCl, (3) buffer saturated phenol, (4) hot 5% SDS and 0.14 M 2-mercaptoethanol and, (5) 0.4 N NaOH. The amount of nuclear protein removed at each of the first four extraction steps was 1, 86, 3 and 11% of the total, respectively. Each extract was characterized by electrophoretic profiles. At each extraction the chromatin was fixed by adding large quantities of a mixture of equal volumes of sodium cacodylate buffered 8% (w/v) glutaraldehyde (pH 6.8) and 2% OsO4 (w/v), directly into (1) an aliquot of the chromatin in extraction fluid, and (2) an aliquot of the chromatin after water washing and swelling. Three size classes of chromatin structure were seen in thin sections prepared for high resolution transmission electron microscopy and stained with uranyl acetate and lead citrate. A thick fiber of about 25 + nm diameter was the predominant large fiber seen in freshly isolated nuclei or in nuclei after salt extraction. This 25 + nm fiber has a substructure consisting of 3.2-5.2 nm diameter fibrils. After water swelling of such freshly isolated or salt extracted nuclei a fiber of about 10 nm diameter was the predominant large fiber instead of the 25 nm diameter fiber. The HCl extraction step which is known to remove histones, caused the disappearance of both the 25 nm and the 10 nm fibers. High magnification (600,000 x) micrographs of the chromatin at all procedural steps, except the last NaOH step, reveal the fibril to be omnipresent. This fibril tends to decrease somewhat in diameter during the protein extraction steps to a 2.5 nm diameter fibril after the hot SDS extraction. A fibril of 2.5 nm diameter is expected of naked double helical DNA stained with a positive stain. The NaOH, which is known to denature DNA, completely destroyed the remaining fibril. We inerpret our results to indicate that the larger chromatin fiber seen in micrographs of thin-sectioned chromatin has a fibrillar substructure which probably represents a double coil of native DNA which may have a thin protein coating of its own. The latter fibril may in turn be wrapped around a hydrophobic histone domain, perhaps reflected in the 10 nm diameter fiber which is seen upon swelling of the chromatin. This 10 nm diameter fiber is thought to be further packaged by folding into the 25 + nm diameter chromatin fiber most frequently reported in thin sections of eukaryotic cell nuclei in situ.

Phospholipids of subcellular organelles isolated from cultured BHK cells

Mitochondrial and nuclei were purified from cultured hamster fibroblasts (BHK21 cells) by centrifugation in sucrose gradients. The phospholipid compositions of the preparations were compared to those of the previously purified plasma membranes, endoplasmic reticulum and lysosomes. The mitochondria had a characteristically high content (approx. 16% of lipid phosphorus) of cardiolipin, which was practically absent from the other purified organelles. The nuclei were enriched in phosphatidylcholine and phosphatidylinositol (approx. 68% and 5% of lipid phosphorus, respectively). Lysobisphosphatidic acid was almost absent from the mitochondria and nuclei, as well as from the plasma membrane and endoplasmic reticulum, which suggests that this phospholipid is confined to the lysosomes of the BHK cell. The nuclei and the mitochondria contained relatively little sphingomyelin, a characteristic lipid of the plasma membrane. The distributions of the total cellular phospholipid and protein between the various organelles were calculated and compared to the corresponding data estimated for the rat liver. The BHK cell contained relatively more phospholipids in the nucleus and the lysosomes than the liver. All the organelles of the BHK cell contained less protein per phospholipid than the equivalent organelles of the liver.

[Chicken erythrocyte nuclei: composition and analysis of phospholipids]

While many works analyse lipid composition of cellular nuclei, essentially of liver, few describe bird erythrocyte nuclei. For them very discordant results are reported due to very different methods of preparation. In the method we adopted a good reproducibility is controlled by electron microscopy, evaluation of specific enzymatic activities and by protein, RNA and DNA determinations. Total lipid content and phospholipid composition were determined showing, in agreement with other works, the predominance of phosphatidylcholine and phosphatidylethanolamine. On the contrary, the nuclear fraction is poor in sphingomyelin, which is essentially a plasma membrane phospholipid.

Experimental disintegration of the nuclear envelope. Evidence for pore-connecting fibrils

The disintegration of the nuclear envelope has been examined in nuclei and nuclear envelopes isolated from amphibian oocytes from amphibian oocytes and rat liver tissue, using different electron microscope techniques (ultrathin sections and negatively or positively stained spread preparations). Various treatments were studied, including disruption by surface tension forces, very low salt concentrations, and nonionic detergents such as Triton C-100 and Nonidet P-40. The highest local stability of the cylinders of nonmembranous pore complex material is emphasized. As progressive disintegration occurred in the membrane regions, a network of fibrils became apparent which interconnects the pore complexes and is distinguished from the pore complex-associated about 15-20 nm thick, located at the level of the inner nuclear membrane, which is recognized in thin sections to bridge the interpore distances. With all disintegraiton treatments a somewhat higher susceptibility of the outer nuclear membrane is notable, but a selective removal does not take place. Final stages of disintegration are generally characterized by the absence of identifiable, membrane-like structures. Analysis of detergent-treated nuclei and nuclear membrane fractions shows almost complete absence of lipid components but retention bo significant amount of glycoproteins with a typical endomembrane-type carbohydrate pattern. Various alternative interpretations of these observations are discussed. From the present observations and those of Aaronson and Blobel (1,2), we favor the notion that threadlike intrinsic membrane components are stabilized by their attachment to the pore complexes, and perhaps also to peripheral nuclear structures,and constitute a detergent-resistant, interpore skeleton meshwork.

Nonhistone proteins control gene expression in reconstituted chromatin

Chromatin was reconstituted from the purified DNA and histones of chicken erythrocytes and the nonhistone proteins of either chicken reticulocytes or chicken liver. Reconstituted chromatins, native chicken reticulocyte chromatin, and free DNA were transcribed with Escherichia coli RNA polymerase and the concentrations of globin-specific sequences in the RNA products were measured by hybridization with [(3)H]DNA complementary to chicken globin messenger RNA. Reticulocyte, but not liver, nonhistone proteins were shown to activate the globin genes in reconstituted erythrocyte chromatin. The transcripts of native and reconstituted chromatins were indistinguishable in respect of both the total yield of the RNA and the fractional yield of globin-specific sequences.

Molecules at the external nuclear surface. Sialic acid of nuclear membranes and electrophoretic mobility of isolated nuclei and nucleoli

The molecules occurring as terminal residues on the external surfaces of nuclei prepared from rat liver by either sucrose-CaCl(2) or citric acid methods and nucleoli derived from the sucrose-CaCl(2) nuclei were studied chemically and electrokinetically. In 0.0145 M NaCl, 4.5% sorbitol, and 0.6 mM NaHCO(3) with pH 7.2 +/- 0.1 at 25 degrees C, the sucrose-CaCl(2) nuclei had an electrophoretic mobility of -1.92 microm/s/V/cm, the citric acid nuclei, -1.63 microm/s/V/cm, and the nucleoli, -2.53 microm/s/V/cm. The citric acid nuclei and the nucleoli contained no measurable sialic acid. The sucrose-CaCl(2) nuclei contained 0.7 nmol of sialic acid/mg nuclear protein; this was essentially located in the nuclear envelope. Treatment of these nuclei with 50 microg neuraminidase/mg protein resulted in release of 0.63 nmol of sialic acid/mg nuclear protein; treatment with 1 % trypsin caused release of 0.39 nmol of the sialic acid/mg nuclear protein. The pH-mobility curves for the particles indicated the sucrose-CaCl(2) nuclei surface had an acid-dissociable group of pK. approximately 2.7 while the pK for the nucleoli was considerably lower. Nucleoli treated with 50 microg neuraminidase/mg particle protein had a mobility of -2.53 microm/s/V/cm while sucrose-CaCl(2) nuclei similarly treated had a mobility of -1.41 microm/s/V/cm. Hyaluronidase at 50 microg/mg protein had no effect on nucleoli mobility but decreased the sucrose-CaCl(2) nuclei mobility to -1.79 microm/s/V/cm. Trypsin at 1 % elevated the electrophoretic mobility of the sucrose-CaCl(2) nuclei slightly but decreased the mobility of the nucleoli to -2.09 microm/s/V/cm. DNase at 50 microg/mg protein had no effect on the mobility of the isolated sucrose-CaCl(2) nuclei but decreased the electrophoretic mobility of the nucleoli to -1.21 microm/s/V/cm. RNase at 50 microg/mg protein also had no effect on the electrophoretic mobility of the sucrose-CaCl(2) nuclei but decreased the nucleoli mobility to -2.10 microm/s/V/cm. Concanavalin A at 50 microg/mg protein did not alter the nucleoli electrophoretic mobility but decreased the sucrose-CaCl(2) nuclei electrophoretic mobility to -1.64 microm/s/V/cm. The results are interpreted to mean that the sucrose-CaCl(2) nuclear external surface contains terminal sialic acid residues in trypsin-sensitive glycoproteins, contains small amounts of hyaluronic acid, is completely devoid of nucleic acids, and binds concanavalin A. The nucleolus surface is interpreted to contain a complex made up of protein, RNA, and primarily DNA, to be devoid of sialic acid and hyaluronic acid, and not to bind concanavalin A.

Glutaraldehyde fixation of isolated eucaryotic nuclei. Evidence for histone-histone proximity

Isolated chicken erythrocyte nuclei have been incubated with dilute concentrations of the bifunctional cross-linking agent glutaraldehyde (0-20 mM) in order to stabilize histone-histone interactions within the native nucleus. The kinetics of the disappearance of acid-soluble histones, free amino groups, and of individual histones have been observed to be pseudo first-order. Apparent first-order rate constants for the disappearance of individual histones correlate with the lysine mole percent of that fraction and follow the ranking, k(app): F1 > F2C > F2B >/= F2A2, F2A1, F3. Histone polymers were observed to form very rapidly during the fixation reaction. Partial fractionation and amino acid analyses of these polymers support the view that they are composed principally of cross-linked (F2C)(n) molecules (where n = 2 to approximately 8). The rate of glutaraldehyde reaction with free amino groups in histones is drastically reduced in solvents that promote chromatin decondensation (i.e., low ionic strengths in the absence of divalent cations) whereas the formation of cross-linked F2C polymers is less severely reduced. It is proposed that some F2C histones exist in close proximity within the isolated erythrocyte nucleus.

Physical studies of isolated eucaryotic nuclei

The degree of chromatin condensation in isolated rat liver nuclei and chicken erythrocyte nuclei was studied by phase-contrast microscopy as a function of solvent pH, K(+) and Mg(++) concentrations Data were represented as "phase" maps, and standard solvent conditions selected that reproducibly yield granular, slightly granular, and homogeneous nuclei Nuclei in these various states were examined by ultraviolet absorption and circular dichroism (CD) spectroscopy, low-angle X-ray diffraction, electron microscopy, and binding capacity for ethidium bromide Homogeneous nuclei exhibited absorption and CD spectra resembling those of isolated nucleohistone. Suspensions of granular nuclei showed marked turbidity and absorption flattening, and a characteristic blue-shift of a crossover wavelength in the CD spectra. In all solvent conditions studied, except pH < 2 3, low-angle X-ray reflections characteristic of the native, presumably superhelical, nucleohistone were observed from pellets of intact nuclei. Threads (100-200 A diameter) were present in the condensed and dispersed phases of nuclei fixed under the standard solvent conditions, and examined in the electron microscope after thin sectioning and staining Nuclei at neutral pH, with different degrees of chromatin condensation, exhibited similar binding capacities for ethidium bromide. These data suggest a model that views chromatin condensation as a close packing of superhelical nucleohistone threads but still permits condensed chromatin to respond rapidly to alterations in solvent environment.

Nuclear membranes from mammalian liver. I. Isolation procedure and general characterization

Nuclear membranes were isolated from rat and pig liver by sonication of highly purified nuclear fractions and subsequent removal of adhering nucleoproteins in a high salt medium. The fractions were examined in the electron microscope by both negative staining and thin sectioning techniques and were found to consist of nuclear envelope fragments of widely varying sizes. Nuclear pore complex constituents still could frequently be recognized. The chemical composition of the nuclear membrane fractions was determined and compared with those of microsomal fractions prepared in parallel. For total nuclei as well as for nuclear membranes and microsomes, various enzyme activities were studied. The results indicate that a similarity exists between both fractions of cytomembranes, nuclear envelope, and endoplasmic reticulum, with respect to their RNA:protein ratio and their content of polar and nonpolar lipids. Both membranous fractions had many proteins in common including some membrane-bound enzymes. Activities in Mg-ATPase and the two examined cytochrome reductases were of the same order of magnitude. The content of cytochrome b(5) as well as of P-450 was markedly lower in the nuclear membranes. The nuclear membranes were found to have a higher buoyant density and to be richer in protein. The glucose-6-phosphatase and Na-K-ATPase activities in the nuclear membrane fraction were very low. In the gel electrophoresis, in addition to many common protein bands, some characteristic ones for either microsomal or nuclear membranous material were detected. Significant small amounts of DNA and RNA were found to remain closely associated with the nuclear envelope fragments. Our findings indicate that nuclear and endoplasmic reticulum membranes which are known to be in morphological continuity have, besides a far-reaching similarity, some characteristic differences.