Stalk segment 4 of the yeast plasma membrane H+-ATPase. Mutational evidence for a role in the E1-E2 conformational change

In the P(2)-type ATPases, there is growing evidence that four alpha-helical stalk segments connect the cytoplasmic part of the molecule, responsible for ATP binding and hydrolysis, to the membrane-embedded part that mediates cation transport. The present study has focused on stalk segment 4, which displays a significant degree of sequence conservation among P(2)-ATPases. When site-directed mutants in this region of the yeast plasma membrane H(+)-ATPase were constructed and expressed in secretory vesicles, more than half of the amino acid substitutions led to a severalfold decrease in the rate of ATP hydrolysis, although they had little or no effect on the coupling between hydrolysis and transport. Strikingly, mutant ATPases bearing single substitutions of 13 consecutive residues from Ile-359 through Gly-371 were highly resistant to inorganic orthovanadate, with IC(50) values at least 10-fold above those seen in the wild-type enzyme. Most of the same mutants also displayed a significant reduction in the K(m) for MgATP and an increase in the pH optimum for ATP hydrolysis. Taken together, these changes in kinetic behavior point to a shift in equilibrium from the E(2) conformation of the ATPase toward the E(1) conformation. The residues from Ile-359 through Gly-371 would occupy three full turns of an alpha-helix, suggesting that this portion of stalk segment 4 may provide a conformationally active link between catalytic sites in the cytoplasm and cation-binding sites in the membrane.

Aldosterone- and testosterone-mediated intracellular calcium response in skeletal muscle cell cultures

Fast nongenomic steroid actions in several cell types seem to be mediated by second messengers such as intracellular calcium ([Ca(2+)](i)) and inositol 1,4,5-trisphosphate (IP(3)). We have shown the presence of both slow calcium transients and IP(3) receptors associated with cell nuclei in cultured skeletal muscle cells. The effect of steroids on [Ca(2+)](i) was monitored in Fluo 3-acetoxymethyl ester-loaded myotubes by either confocal microscopy or fluorescence microscopy, with the use of out-of-focus fluorescence elimination. The mass of IP(3) was determined by radioreceptor displacement assay. [Ca(2+)](i) changes after either aldosterone (10-100 nM) or testosterone (50-100 nM) were observed; a relatively fast (<2 min) calcium transient, frequently accompanied by oscillations, was evident with both hormones. A slow rise in [Ca(2+)](i) that reached its maximum after a 30-min exposure to aldosterone was also observed. Calcium responses seem to be fairly specific for aldosterone and testosterone, because several other steroid hormones do not induce detectable changes in fluorescence, even at 100-fold higher concentrations. The mass of IP(3) increased transiently to reach two- to threefold the basal level 45 s after addition of either aldosterone or testosterone, and the IP(3) transient was more rapid than the fast calcium signal. Spironolactone, an inhibitor of the intracellular aldosterone receptor, or cyproterone acetate, an inhibitor of the testosterone receptor, had no effect on the fast [Ca(2+)](i) signal or in the increase in IP(3) mass. These signals could mean that there are distinct nongenomic pathways for the action of these two steroids in skeletal muscle cells.

Toxic and trace elements in liver, kidney and meat from cattle slaughtered in Galicia (NW Spain)

The aims of this study were to determine the levels of some toxic and trace metals in cattle meat in Spain and to compare them with concentrations in cattle elsewhere and to maximum acceptable levels. Arsenic, cadmium, lead, copper and zinc concentrations in the liver, kidney and muscle (meat) from 438 calves (6-10 months old) and 56 cows (2-16 years old) slaughtered in Galicia (NW Spain) in 1996 were quantified. The arithmetic mean fresh weight concentrations in calf liver, kidney and muscle respectively were 0.043, 0.055, 0.004 mg/kg for arsenic, 0.032, 0.070, 0.001 mg/kg for cadmium, 0.053, 0.052, 0.009 mg/kg for lead, 64.6, 4.91, 0.677 mg/kg for copper and 47.7, 14.4, 47.8 mg/kg for zinc. In cows, these concentrations were 0.046, 0.068, 0.005 mg/kg (arsenic), 0.097, 0.458, 0.001 mg/kg (cadmium), 0.057, 0.066, 0.017 mg/kg (lead), 60.3, 3.67, 1.26 mg/kg (copper) and 59.8, 20.0, 52.7 mg/kg (zinc). Except for copper levels in the liver which were high, metal concentrations in cattle were generally low in Galicia and broadly similar to those in the rest of Europe, Australia and Canada. Arsenic, cadmium and lead concentrations in Galician cattle rarely exceeded acceptable maximum concentrations that have been adopted by many countries. Copper and zinc concentrations in Galician cattle did exceed acceptable maximum concentrations but the frequency with which this occurred depended upon which acceptable maximum concentration was used; regulatory values differ markedly between countries.

Biochemical, electrophoretic and immunohistochemical aspects of malate dehydrogenase in truffles (Ascomycotina)

The malate dehydrogenase (MDH; EC 1.1.1.37; L-malate-NAD(+)-oxidoreductase) activities of truffles of the genus Tuber (Tuber melanosporum Vittad., Tuber brumale Vittad., Tuber aestivum Vittad., Tuber magnatum Pico, Tuber rufum Pico) have been characterized with regard to the K(m) and V(max) values in the direct and reverse reactions. The isoelectrofocusing has revealed bands showing pI values ranging from pH 5.85 to 7.8. The MDH of T. melanosporum has been partially purified by hydroxyapatite treatment, DEAE-cellulose and Sephadex G-75 columns. With the partially purified T. melanosporum MDH activity polyclonal anti-T. melanosporum MDH antibodies have been prepared and used to localize MDH in the mycorrhizae and ascocarps of T. melanosporum. These antibodies inhibit T. melanosporum MDH activity as well as that of T. magnatum but not that of rabbit liver; this supports the specificity of the MDH antibodies used to localize MDH in truffle tissues.

Arsenic, cadmium, lead, copper and zinc in cattle from Galicia, NW Spain

Knowledge of trace and toxic metal concentrations in livestock is important for assessing the effects of pollutants on domestic animals and contaminant intakes by humans. Metal levels in cattle have been measured in various countries but not in Spain. In this study, the (wet wt.) concentrations of three toxic elements (arsenic, cadmium, lead) and two trace elements (copper, zinc) were quantified in the liver (Li), kidney (Ki), muscle (M) and blood (Bl) of calves (males and females between 6 and 10 months old) and cows (2-16 years old) from Galicia, NW Spain. For the toxic elements, geometric mean concentrations of arsenic in calves (sexes combined) and cows were 10.8 and 10.2 microg/kg (Li), 11.3 and 15.2 microg/kg (Ki), 3.75 and 4.25 microg/kg (M), 3.23 and 2.92 microg/l (Bl). The corresponding cadmium concentrations were 7.78 and 83.3 microg/kg (Li), 54.3 and 388 microg/kg (Ki), 0.839 and 0.944 microg/kg (M), 0.373 and 0.449 microg/l (Bl). Geometric mean concentrations of lead in calves and cows were similarly low and were 33.0 and 47.5 microg/kg (Li), 38.9 and 58.3 microg/kg (Ki), 6.37 and 12.5 microg/kg (M), 5.47 and 12.2 microg/l (Bl). Sex had almost no effect on the amount of toxic metal accumulated except that kidney cadmium concentrations were significantly higher in females than males. Age did influence accumulation; cadmium and lead (but not arsenic) concentrations in most tissues were significantly greater in cows than female calves. For the trace elements, geometric mean copper levels in calf and cow tissues were 49.9 and 36.6 mg/kg (Li), 4.27 and 3.63 mg/kg (Ki), 0.649 and 1.68 mg/kg (M) and 0.878 and 0.890 mg/l (Bl). The corresponding zinc concentrations were 46.3 and 52.5 mg/kg (Li), 14.2 and 20.7 mg/kg (Ki), 47.3 and 52.5 mg/kg (M) and 2.80 and 2.22 mg/l (Bl). Female calves had significantly higher levels than males of muscle zinc and blood copper and zinc. Female calves accumulated more copper but less zinc in the liver and kidneys compared with cows; this may have been associated with the chronic, low-level cadmium accumulation observed in cows. Overall, the levels of arsenic, cadmium, lead and zinc in cattle in Galicia do not constitute a risk for animal health. However, up to 20% of cattle in some regions in Galicia had levels of copper in the liver that exceeded 150 mg/kg wet wt. These animals may be at risk from copper poisoning.

Biogenesis and function of the yeast plasma-membrane H(+)-ATPase

One of the most abundant proteins in the yeast plasma membrane is the P-type H(+)-ATPase that pumps protons out of the cell, supplying the driving force for a wide array of H(+)-dependent cotransporters. The ATPase is a 100 kDa polypeptide, anchored in the lipid bilayer by 10 transmembrane alpha-helices. It is structurally and functionally related to the P-type Na(+),K(+)-, H(+),K(+)- and Ca(2+)-ATPases of animal cells and the H(+)-ATPases of plant cells, and it shares with them a characteristic reaction mechanism in which ATP is split to ADP and inorganic phosphate (P(i)) via a covalent beta-aspartyl phosphate intermediate. Cryoelectron microscopic images of the H(+)-ATPase of Neurospora crassa and the sarcoplasmic reticulum Ca(2+)-ATPase of animal cells have recently been obtained at 8 nm resolution. The membrane-embedded portion of the molecule, which presumably houses the cation translocation pathway, is seen to be connected via a narrow stalk to a large, multidomained cytoplasmic portion, known to contain the ATP-binding and phosphorylation sites. In parallel with the structural studies, efforts are being made to dissect structure/function relationships in several P-type ATPases by means of site-directed mutagenesis. This paper reviews three phenotypically distinct classes of mutant that have resulted from work on the yeast PMA1 H(+)-ATPase: (1) mutant ATPases that are poorly folded and retained in the endoplasmic reticulum; (2) mutants in which the conformational equilibrium has been shifted from the E(2) state, characterized by high affinity for vanadate, to the E(1) state, characterized by high affinity for ATP; and (3) mutants with altered coupling between ATP hydrolysis and proton pumping. Although much remains to be learned before the transport mechanism can be fully understood, these mutants serve to identify critical parts of the polypeptide that are required for protein folding, conformational change and H(+):ATP coupling.

Inhibition of L-tyrosine-induced micronuclei production by phenylthiourea in human melanoma cells

It was previously found that L-tyrosine oxidation product(s) are cytotoxic, genotoxic and increase the sister chromatid exchange (SCE) levels in human melanoma cells. In this work, the micronucleus assay has been performed on human melanotic and amelanotic melanoma cell lines (Carl-1 MEL and AMEL) in the presence of 1.0, 0.5 and 0.1 mM L-tyrosine concentrations to investigate if melanin synthesis intermediate(s) increase micronuclei production. L-Tyrosine oxidation product(s) increased the frequency of micronuclei in melanoma cells; 0.1 mM phenylthiourea (PTU), an inhibitor of L-tyrosine oxidation by tyrosinase, lowered the micronucleus production to the control levels. The culture of melanoma cells with high L-tyrosine in the culture medium resulted in a positive response to an ELISA-based apoptotic test. For comparison the effect of L-tyrosine on micronuclei production in human amelanotic melanoma cells was also investigated; the micronucleus production in the presence of 1 mM L-tyrosine in the culture medium was lower than that found with melanotic melanoma cells of the same cell line. The data suggest that melanin synthesis intermediates arising from L-tyrosine oxidation may cause micronuclei production in Carl-1 human melanoma cells; the addition of PTU in the presence of L-tyrosine decreased the frequency of micronuclei to about the control values thus the inhibition of melanogenesis may have some clinical implication in melanotic melanoma.

[Tics disease (Gilles de la Tourette syndrome): clinical characteristics of 70 patients]

BACKGROUND

Tourette's syndrome is a childhood-onset hereditary neurobehavioural disorder believed to occur without geographical restrictions. Although there have been reports of this disorder worldwide just a few are from Latin America.

AIM

To report a preliminary experience with a series of 70 patients and to review recent advances in this disorder.

PATIENTS AND METHOD

We reviewed patients seen in pediatric and adult neurological clinics in Santiago, Chile, all of whom fulfilled clinical diagnostic criteria for Tourette Syndrome.

RESULTS

Seventy patients were studied, 54 males (77.1%) and 16 females (22.8%), their mean age at first evaluation was 13.6 years (range 2-46). The mean age of onset of symptoms was 6.4 (range 2-20), the mean time of follow-up was 3 years. Fifty-eight patients showed simple motor tics (blinking, facial grimacing, shoulder shrugging), whereas dystonic tics like head jerking were seen in 38 patients, torticollis in 6 and oculogyric movements in 2. Complex motor tics like jumping, antics, trunk bending and head shaking were present in 16 subjects. Vocal tics were predominantly of the simple type: sniffing, throat clearing, blowing, and whistling. Complex vocal tics were seen in 12 patients, five cases showed palilalia, 3 echolalia and only six displayed coprolalia (8.5%). Tics were of mild to moderate severity in most patients. Obsessive-compulsive disorder was observed in 22.8% and attention deficit and hyperactivity disorder were present in 35.7%. Forty-five patients (64.2%) had a first degree relative with tics, nine patients (12.8%) had a family history of obsessive-compulsive disorder. The current evidence involving desinhibition of cortico-striatum-thalamic-cortical neuronal circuits in the pathogenesis of this disorder is analyzed.

CONCLUSION

Our report supports the recognized clinical homogeneity and genetical basis of Tourette's syndrome regardless of geographical region and ethnic origin.

[Long-term follow up of asymptomatic chagasic individuals with intraventricular conduction disturbances, correlating with non-chagasic patients]

This prospective study was designed to evaluate intraventricular conduction disturbances in asymptomatic patients with Chagas' disease, and patients with primary sclerosis of the conducting system of the heart (Lev-Lenègre's disease). Eighty-four asymptomatic individuals with right- or left-bundle branch block were submitted to electrophysiological evaluation and long-term follow-up. Fifty-five had positive serologic blood tests for Chagas' disease and 29 had Lev-Lenègre's disease. Mean-age of 45 years in chagasic and 63 in non-chagasic patients (p< 0.001). There were 54 (98.2%) with right-bundle branch block in chagasic and 14 (48.3%) among non-chagasic patients (p <0.001). Sinus nodal and atrioventricular nodal functions presented no differences in either group. However, mean HV interval was greater in the NCH than in the CH group (p< 0.01). After a mean follow-up of 121 +/- 63.75 months among chagasic and 94.97 +/- 67.55 months among non-chagasic patients, total mortality was 20 (36.6%) patients in chagasic and 9 (31%) among non-chagasic patients (NS). Cardiac death was recorded in 17 (85%) individuals among chagasic and 3 (33.3%) among non-chagasic patients(p <0.05). Sudden death occurred in 10 (50%) among chagasic and was not observed in non-chagasic patients (p <0. 01).

IN CONCLUSION

1. Asymptomatic chagasic individuals with intraventricular conduction disturbances showed higher cardiac mortality, sudden or non-sudden death in relation to non-chagasic individuals. 2. The evaluated electrophysiological parameters were of no prognostic value in relation to mortality, although programmed ventricular stimulation was not performed.

The effect of intrastriatal injection of liposome-entrapped tyrosinase on the dopamine levels in the rat brain

Parkinson's disease is a neurodegenerative disorder which is mainly characterized by degeneration of the dopaminergic cells in the nigro-striatal system. Due to a lowered L-tyrosine 3-monooxygenase activity, L-tyrosine is not sufficiently transformed to L-DOPA. To date the most common therapy is the administration of the dopamine precursor L-DOPA, with severe collateral effects. Therefore, the substitution of the lacking tyrosine hydroxylase with tyrosinase might be a novel therapeutical approach that would generate specifically L-DOPA from L-tyrosine. We present here evidence that stereotaxic injection of liposome-entrapped tyrosinase is able to significatively increase the levels of dopamine in the rat brain. The catecholamines L-DOPA, dopamine, L-epinephrine, L-norepinephrine were extracted by acid treatment from the brains and detected by HPLC.

Effect of tyrosinase inhibitors on Tuber borchii mycelium growth in vitro

This paper reports the effect of the tyrosinase (monophenol o-diphenol:oxygen oxidoreductase; EC 1.14.18.1) inhibitors diethyldithiocarbamate (DETC), L-tropolone, kojic acid, phenylthiourea (PTU) and L-mimosine on the in vitro growth of Tuber borchii (a white truffle) mycelium. A significant inhibitory effect on mycelium growth was observed for DETC, PTU and L-tropolone (0% growth compared to control at 100 microg ml(-1) DETC, PTU and L-tropolone and at 10 microg ml(-1) DETC and L-tropolone). As a comparison the action of the same inhibitors was also tested on the growth and pigmentation of the mould Cladosporium sphaerospermum. In the presence of CuSO(4) 10(-6) M T. borchii mycelium acquired pigmentation (as rounded aggregates compared to control revealed by SEM microscopy). Tyrosinase activity in the extract from T. borchii mycelium (18-day culture) was detected spectrophotometrically.

Effect of physiological stage and nutritional management on some serum metabolite concentrations in Assaf ovine breed

Abstract. The Assaf breed represents a small percentage of the total dairy ovine census in the Castilla-León region and there are no studies conducted solely on this breed for understanding their physiology, nutritional requirements, diseases, management and appropiate beeding methods. The aim of the present report is to evaluate and to comment, in field conditions on, the nutritional management developed in a flock of Assaf ewes, studying the effects on energy metabolism during different physiological conditions (Anoestrus, Pregnancy and Lactation). On the other hand, the effect of litter size was also recorded. The study was conducted on thirty-five ewes of the Assaf breed housed in an intensive management system and randomly assigned to experimental and control groups, the latter divided into singles and twins. All the animals were housed in the same environmental conditions, and received the same diet. The metabolic parameters measured were serum glucose, cholesterol, tnglycendes and NEFA. Our results demonstrate that it is important to consider two critical moments: firstly the early pregnancy period, where the administration of a maintenance diet based on low-energy foods (alfalfa hay) is not enough for energy demands, as was shown by the significant decrease in glucose and triglyceride values; and secondly, late pregnancy, where excessive concentrate intake must be avoided in order to prevent future metabolic diseases and obesity. It has been observed that serum glucose and NEFA values are influenced more by nutritional management than by physiological conditions

Multiple unfolded states of glutathione transferase bbGSTP1-1 by guanidinium chloride

Inactivation, dissociation, and unfolding of the homodimeric glutathione transferase (bbGSTP1-1) from Bufo bufo embryos were investigated at equilibrium, using guanidinium chloride (GdmCl) as denaturant. Protein transitions were monitored by enzyme activity, intrinsic fluorescence, far UV circular dichroism, glutaraldehyde cross-linking, and gel-filtration chromatography. At low denaturant concentrations (less than 0.5 M), reversible inactivation of the enzyme occurs. At denaturant concentrations between 0.5 and 1.5 M the enzyme progressively dissociates into structured monomers. At higher denaturant concentrations the monomers unfold completely. Refolding studies indicate that a total reactivation occurs only by starting from the enzyme denatured at concentrations below 0.5 M. The enzyme denatured at GdmCl concentrations higher than 0.5 M only partially refolds. Globally our results indicate that unfolding of the amphibian bbGSTP1-1 is a multistep process, i.e., inactivation of the structured dimer, dissociation into partially structured monomers, followed by complete unfolding.

[Adult onset subacute sclerosing panencephalitis. Report of two cases with atypical presentation]

Subacute sclerosing panencephalitis is an infrequent central nervous system viral disease and is a late manifestation of persistent infection by a mutant form of measles virus. Since it affects mainly children and teenagers, the diagnosis in older ages is difficult. Its main clinical symptoms are cognitive impairment, behavioral disturbances and myoclonia. We report two males, aged 21 and 22 years old, presenting with the disease with atypical manifestations. One had a catatonic syndrome and the other, amaurosis. The recognition of the different presentation forms of the disease, endemic in developing countries, allows an earlier diagnosis and a more efficient treatment, when available.

Morphology and amplitude values of the P and T waves in the electrocardiograms of Spanish-bred horses of different ages

This investigation was undertaken to determine values of electrocardiographic parameters in Spanish-bred horses at different stages of growth. The study was carried out on 179 healthy Spanish-bred (Andalusian) horses (98 females and 81 males), which were aged between 1 month and 17 years. The ECGs showed P waves of different configurations. The bifid shape deflection of the P wave was generally more frequent than the simple one in animals from 6 months of age. The first component of bifid P waves (P1) did not vary in a statistically significant way with increasing age, showing a mean value of 0.105 mV. The amplitudes of the P2 (the second component of the bifid P waves) and simple P waves showed statistically significant differences between the age groups. The highest values were found in animals up to 3 months and over 2 years of age. Several configurations of the T wave were observed in the different age groups: a negative shape was generally present for the youngest animals (foals up to 2 years old); the biphasic (/+) pattern became more frequent in animals 3 and 4 years old. In adult horses the positive configuration was the most frequent. No statistically significant differences according to age were found for the amplitude values of the different T-wave configurations.

[Chorea induced by oral contraceptives. Report of two cases]

We report two women using oral contraceptives, aged 17 and 33 years old, who presented with hemichorea. In both patients all other possible causes of chorea were discarded and the disease disappeared when contraceptives were discontinued. Four months later, the 33 years old patient used again oral contraceptives and chorea reappeared. This rare complication of contraceptive use has been previously reported in young and mainly nulliparous women.

[Severe hyponatremia during treatment with fluoxetine]

Serotonin reuptake inhibitors, used as antidepressants, may cause hyponatremia due to a syndrome of inappropriate antidiuretic hormone, specially in elders. Thirty cases with such complication have been reported in the last six years. We report a 76 years old female with a hypertensive cardiopathy and paroxysmal atrial fibrillation treated with amlodipine and sotalol. Five days after starting fluoxetine, the patient presented with a confusional state, gait instability and tremor. Laboratory assessment disclosed a plasma sodium of 115 meq/L. Fluoxetine was discontinued and fluids were restricted. The clinical condition of the patient improved and hyponatremia abated. Hyponatremia must be born in mind as a potential side effect of serotonin reuptake inhibitors.

Age-dependent ultrastructural alterations and biochemical response of rat skeletal muscle after hypoxic or hyperoxic treatments

This work deals with the antioxidant enzymatic response and the ultrastructural aspects of the skeletal muscle of young and aged rats kept under hypoxic or hyperoxic normobaric conditions. It is in fact well known that the supply of oxygen at concentrations higher or lower than those occurring under normal conditions can promote oxidative processes that can cause tissue damage. The enzymes investigated were both those directly involved in reactive oxygen species (ROS) scavenging (superoxide dismutase, catalase and selenium-dependent glutathione peroxidase), and those challenged with the detoxication of cytotoxic compounds produced by the action of ROS on biological molecules (glutathione transferase, glyoxalase I, glutathione reductase), in order to obtain a comparative view of the defence strategies used with respect to aging. Our results support the hypothesis that one of the major contributors to the aging process is the oxidative damage produced at least in part by an impairment of the antioxidant enzymatic system. This makes the aged organism particularly susceptible to oxidative stress injury and to the related degenerative diseases, especially in those tissues with high demand for oxidative metabolism.

Selective glutathione depletion of mitochondria by ethanol sensitizes hepatocytes to tumor necrosis factor

BACKGROUND & AIMS

Tumor necrosis factor (TNF)-alpha induces cell injury by generating oxidative stress from mitochondria. The purpose of this study was to determine the effect of ethanol on the sensitization of hepatocytes to TNF-alpha.

METHODS

Cultured hepatocytes from ethanol-fed (ethanol hepatocytes) or pair-fed (control hepatocytes) rats were exposed to TNF-alpha, and the extent of oxidative stress, gene expression, and viability were evaluated.

RESULTS

Ethanol hepatocytes, which develop a selective deficiency of mitochondrial glutathione (mGSH), showed marked susceptibility to TNF-alpha. The susceptibility to TNF-alpha, manifested as necrosis rather than apoptosis, was accompanied by a progressive increase in hydrogen peroxide that correlated inversely with cell survival. Nuclear factor kappaB activation by TNF-alpha was significantly greater in ethanol hepatocytes than in control hepatocytes, an effect paralleled by the expression of cytokine-induced neutrophil chemoattractant. Similar sensitization of normal hepatocytes to TNF-alpha was obtained by depleting the mitochondrial pool of GSH with 3-hydroxyl-4-pentenoate. Restoration of mGSH by S-adenosyl-L-methionine or by GSH-ethyl ester prevented the increased susceptibility of ethanol hepatocytes to TNF-alpha.

CONCLUSIONS

These results indicate that mGSH controls the fate of hepatocytes in response to TNF-alpha. Its depletion caused by alcohol consumption amplifies the power of TNF-alpha to generate reactive oxygen species, compromising mitochondrial and cellular functions that culminate in cell death.

Differential response of human melanoma and Ehrlich ascites cells in vitro to the ribosome-inactivating protein luffin

The cytotoxicity and inhibitory effect on proliferation of the type 1 ribosome-inactivating protein luffin purified from the seeds of Luffa aegyptiaca were investigated both in human metastatic melanoma cells and in murine Ehrlich ascites tumour cells. Results indicate that luffin from the seeds of Luffa aegyptiaca is cytotoxic to the cell lines tested, with approximately 10 times greater potency in Ehrlich cells. Luffin was found to induce an increase in cytosolic oligonucleosome-bound DNA in both melanoma and Ehrlich ascites tumour cells, the level of DNA fragmentation in the former cell line being higher than in the latter. Experiments with melanoma cells indicate that an increase in cytosolic nucleosomes could be supportive of apoptosis as the type of cell death induced by luffin.

[The relation of Helicobacter pylori with dysplasia and stomach neoplasms in Costa Rica]

Occurrence of the bacterium Helicobacter pylori was compared for two Costa Rican sites with contrasting levels of gastric cancer incidence, Poás (incidence 15.13%) and Puriscal (83.53%). A sample of 185 adults of similar age and sex proportions was studied in each site, using both H. pylori antiserum tests and gastroscopy to collect two biopsies per case. No clear association between H. pylori and gastric cancer was found.

[Pituitary apoplexy followed by endocrine remission. Report of two cases]

Pituitary apoplexy is rare and endocrine remission in patients with apopletic secreting pituitary adenomas is even rarer. This study reports on two patients with pituitary macroadenomas (one with Cushing's disease and the other with acromegaly) in whom endocrine remission occurred after apoplexy. The first patient had Cushing's disease and had an ictus of headache and vomiting after which she started a progressive remission of hypercortisolism. A post-apoplexy MRI disclosed persistence of a sellar and supra-sellar mass. She was submitted to transesphenoidal surgery. An hypertensive hemorrhagic cyst was found with no tumor. The second patient had acromegaly. While performing a LHRH-stimulation test he had an ictus of headache, vomiting, no visual loss and appearance of diabetes insipidus. A CT scan disclosed an intrasellar hematoma. Despite the size of the tumor and since there was no visual impairment, this patient was followed up without surgery. Imaging follow-up showed a progressive shrinkage and disappearance of the mass, which was corroborated by endocrine remission. A high rate of recurrence is reported in such patients in the literature. Both patients are being currently followed-up on a long-term basis.

The influence of reproductive stage on the selenium status of sheep in a low-selenium region

The selenium status of sheep was evaluated during the reproductive stage in a region of low selenium level. Serum selenium concentration, whole blood glutathione peroxidase activity (GSH-Px), which is a good indicator of protection against oxidative damage, as well as the activities of creatine kinase (CK) and aspartate aminotransferase (AST), the plasma indicators of muscle damage, were evaluated in a group of ewes during gestation and lactation and in their lambs. The selenium requirements of ewes were found to increase during lactation. There were no differences in GSH-Px activity between the experimental and the control groups throughout the reproductive stage. In the second half of pregnancy GSH-Px activity was subnormal. In spite of this, no evidence of existing pathologic conditions associated with selenium deficiency was found, since the muscle markers CK and AST were within the normal range. In the same way, no distinct symptoms of nutritional myopathy were observed in the lambs, suggesting that the low selenium level found in the ewes did not cause alterations in their development.

Oxidative damage of mitochondrial and nuclear DNA induced by ionizing radiation in human hepatoblastoma cells

PURPOSE

Since reactive oxygen species (ROS) act as mediators of radiation-induced cellular damage, the aim of our studies was to determine the effects of ionizing radiation on the regulation of hepatocellular reduced glutathione (GSH), survival and integrity of nuclear and mitochondrial DNA (mtDNA) in human hepatoblastoma cells (Hep G2) depleted of GSH prior to radiation.

METHODS AND MATERIALS

GSH, oxidized glutathione (GSSG), and generation of ROS were determined in irradiated (50-500 cGy) Hep G2 cells. Clonogenic survival, nuclear DNA fragmentation, and integrity of mtDNA were assessed in cells depleted of GSH prior to radiation.

RESULTS

Radiation of Hep G2 cells (50-400 cGy) resulted in a dose-dependent generation of ROS, an effect accompanied by a decrease of reduced GSH, ranging from a 15% decrease for 50 cGy to a 25% decrease for 400 cGy and decreased GSH/GSSG from a ratio of 17 to a ratio of 7 for controls and from 16 to 6 for diethyl maleate (DEM)-treated cells. Depletion of GSH prior to radiation accentuated the increase of ROS by 40-50%. The depletion of GSH by radiation was apparent in different subcellular sites, being particularly significant in mitochondria. Furthermore, depletion of nuclear GSH to 50-60% of initial values prior to irradiation (400 cGy) resulted in DNA fragmentation and apoptosis. Consequently, the survival of Hep G2 to radiation was reduced from 25% of cells not depleted of GSH to 10% of GSH-depleted cells. Fitting the survival rate of cells as a function of GSH using a theoretical model confirmed cellular GSH as a key factor in determining intrinsic sensitivity of Hep G2 cells to radiation. mtDNA displayed an increased susceptibility to the radiation-induced loss of integrity compared to nuclear DNA, an effect that was potentiated by GSH depletion in mitochondria (10-15% intact mtDNA in GSH-depleted cells vs. 25-30% of repleted cells).

CONCLUSION

GSH plays a critical protective role in maintaining nuclear and mtDNA functional integrity, determining the intrinsic radiosensitivity of Hep G2. Although the DNA repair is a complex process that is not yet completely understood, the protective role of GSH probably does not seem to involve the repair of classical DNA damage but may relate to modification of DNA damage dependent signaling.

Evaluation of the safety, immunogenicity, and pharmacokinetic profile of a new, highly purified, heat-treated equine rabies immunoglobulin, administered either alone or in association with a purified, Vero-cell rabies vaccine

A clinical evaluation of a new, purified, heat-treated equine rabies immunoglobulin (PHT-Erig), F(ab')2 preparation, was carried out in Thailand and in the Philippines-two countries where rabies is endemic. An initial prospective, randomised, controlled trial (Study 1), compared the safety and pharmacokinetics (serum concentrations of rabies antibodies) after administration either of PHT-Erig or of a commercially-available, equine rabies immune globulin (Erig PMC). A second trial (Study 2) simulated post-exposure rabies prophylaxis by using a reference cell culture vaccine, the purified Vero-cell rabies vaccine (PVRV), administered in association with either Erig PMC or PHT-Erig. In Study 1, 27 healthy, Thai adults received a 40 IU kg(-1) dose of either Erig PMC (n = 12) or PHT-Erig (n = 15) via the intramuscular (i.m.) route; half of the dose was injected into the deltoid area and the other half into the buttocks. Serum for rabies antibody determination and F(ab')2 concentration was collected at hours (H) 0, 6 and 12, and on day (D) 2, 3, 4, 6, 8, 10, 12 and 15. Both products were safe, with no serious adverse events, and in particular, no anaphylactic reactions or serum sickness was reported. A statistical comparison of the pharmacokinetic parameters did not demonstrate bioequivalence of the two products. Nonetheless, the relative bioavailability of 93% and the similar absorption rates suggest the pharmacokinetic profiles of Erig and PHT-Erig are similar. The antibody level in either group were low throughout the 15-day study period. The geometric mean titer (GMT) values ranged from group 0.027-0.117 IU ml(-1) in the Erig group and from 0.029 to 0.072 IU ml(-1) in the PHT-Erig. There was no significant difference between the evolution of GMT values for the two groups. In Study 2, 71 healthy volunteers received 40 IU kg(-1) via the intramuscular route of either Erig PMC (n = 36) or PHT-Erig (n = 35) on D0, in association with five doses of PVRV on D0, D3, D7, D14 and D28. The safety evaluation was performed during the 28-day follow-up and serum samples for anti-rabies antibody titration were collected on D0 (before injection) D3, D7, D14 and D28. No serious reactions were reported in either group. In particular, no immediate (anaphylactic type) or delayed (serum sickness) allergic reactions were observed. Over the 28-day follow-up period, GMT profiles of the two groups were statistically equivalent. On D14, 100% of the subjects had protective antibody titers (anti-rabies antibodies > or = 0.5 IU ml(-1), which is the WHO-recommended level of seroconversion), and Erig PMC and PHT-Erig were indistinguishable according to the clinical definition chosen. On D28, the GMT values were 33.2 IU ml(-1) (95% CI, 23.8-46.1 IU ml(-1)) in the Erig PMC/PVRV group and 31.4 IU ml(-1) (95% confidence interval, CI, 23.4-42.2 IU ml(-1)) in the PHT-Erig/PVRV group, showing evidence of adequate vaccine-induced antibody responses in both groups. The increased purity, the heat-treatment step introduced in the manufacturing process of PHT-Erig, and the good clinical results substantiate the use of this new generation, purified equine F(ab')2 preparation in the post-exposure prophylaxis of rabies.

Effect of methylglyoxal on Bufo bufo embryo development: morphological and biochemical aspects

Methylglyoxal (2-oxopropanal) is a cytotoxic compound that can be formed endogenously as a by-product of glycolytic pathway; so its concentration is expected to increase when glycolysis activity increases such as during embryo development. In this work we study the effect of exogenous methylglyoxal on development and embryo viability during Bufo Bufo development and on the enzymes and cofactors involved in its detoxication process (glyoxalase I and II, reduced glutathione and glyceraldehyde 3-phosphate dehydrogenase). The results show that exogenous methylglyoxal does not affect the enzymatic pattern until stage 20, while it induces a significant activity decrease of the tested enzymes at stage 25. On the contrary methylglyoxal positively influences the reduced glutathione concentration at all the considered stages. At morphological and histological levels methylglyoxal causes a strong retardation of cell division in the early stages, that results in various abnormalities in the late development. In conclusion, methylglyoxal enters the embryo and is antiproliferative and teratogenic: the data further supports the hypothesis of the importance of the glyoxalase system in the process of cell growth and division.

Effects of steroid treatment on activation of nuclear factor kappaB in patients with inflammatory bowel disease

Nuclear factor kappB (NFkappaB) is a transcription factor that controls several genes important for immunity and inflammation. The aim of this study was to assess if activation of NFkappaB plays a role in the pathogenesis of inflammatory bowel disease (IBD), and whether steroid treatment affects NFkappaB activation. Activation of NFkappaB was analysed in colon biopsy samples of 13 patients with active IBD (8 Crohn's colitis, 5 ulcerative colitis) by electrophoretic mobility-shift assays, under basal conditions and 3 weeks after treatment with 0.75 mg kg(-1) day(-1) prednisolone. The presence of interleukin-8 mRNA in biopsies was assessed by RT-PCR. A specific NFkappaB band was present in all nuclear extracts from inflamed mucosa, whereas the band was barely detectable in uninflamed colonic mucosa. NFkappaB bands were super-shifted by antibodies against p50 subunit, whereas antibodies against p65, p52, c-Rel, or Rel B did not modify the mobility of the band. Increased interleukin-8 mRNA was detected at the same sites of NFkappaB activation. Steroid-induced healing of colonic inflammation was associated with disappearance of NFkappaB from nuclear extracts. These results support the notion that NFkappaB plays an important role in the pathogenesis of IBD, and that blockade of NFkappaB activation is one of the mechanisms by which steroids suppress the inflammatory cascade in IBD.

Transcriptional regulation of the heavy subunit chain of gamma-glutamylcysteine synthetase by ionizing radiation

Since glutathione (GSH) protects against oxidative stress, we determined the regulation of cellular GSH by ionizing radiation in human hepatoblastoma cells, HepG2. The levels of GSH increased in irradiated HepG2 due to a greater gamma-glutamylcysteine synthetase (gamma-GCS) activity, which was paralleled by gamma-GCS heavy subunit chain (gamma-GCS-HS) mRNA levels. Transcription of deletion constructs of the gamma-GCS-HS promoter cloned in a reporter vector was associated with activator protein-1 (AP-1), consistent with the DNA binding of AP-1 in nuclear extracts of irradiated HepG2. Hence, the transcriptional regulation of gamma-GCS by ionizing radiation emerges as an adaptive mechanism, which may be of significance to control the consequences of the oxidative stress induced by radiation.

Adaptive response of human melanoma cells to methylglyoxal injury

The effects of methylglyoxal on the growth of a line of human melanoma cells are investigated. Methylglyoxal inhibits cell growth in a dose-dependent manner and causes an increase in glyceraldehyde 3-phosphate dehydrogenase, and glyoxalase 1 and glyoxalase 2 specific activities. The cellular response to increasing concentrations of methylglyoxal in the culture medium is also studied by measuring L-lactate production, reduced-oxidized glutathione levels and apoptotic cell death. Methylglyoxal seems to promote a change of cell population phenotypic repertoire toward a more monomorphic phenotype. In conclusion, methylglyoxal seems to induce an enzymatic cellular response that lowers methylglyoxal levels and selects the most resistant cells.

Glyoxalases activity during Bufo bufo embryo development

In this work we have investigated the expression of glyoxalase I (GLO I) and glyoxalase II (GLO II) activities during Bufo bufo embryo development and in some tissues of both male and female adult animals, in order to study how they correlate with cell proliferation and differentiation. The results show that both the activities are expressed at significant levels from the earliest developmental stages, reaching the highest values at the end of embryonic development (stage 25). The GLO I/GLO II ratio is very high at the beginning of the development and then gradually decreases as the development goes on. These data emphasize the importance of GLO I activity in the phases in which elevated cell division is taking place. In the differentiated tissues, a peculiar sexual dimorphism in both GLO I and GLO II activities, with higher values in female than in male, was found. GLO I embryonic activity levels are comparable to those found in female differentiated tissues, but significantly higher than those detected in male differentiated tissues. On the contrary, the GLO II activities found in the adult tissues were always higher than those found in embryos. These results further support the idea that high GLO I/GLO II ratios are a characteristic of the proliferative status, which assures a good scavenging action against the potentially cytotoxic and cytostatic effect of methylglyoxal.

Oxidative stress: role of mitochondria and protection by glutathione

Increasing evidence has unraveled a dual functional role of mitochondria as suppliers of the energy required for cell viability, and critical players in the pathway leading to cell death. Consequence of their physiological role in the oxidative phosphorylation is the generation of reactive oxygen species (ROS) as byproducts of the consumption of molecular oxygen in the electron transport chain. Superoxide anion and hydrogen peroxide produced during aerobic respiration are precursors of hydroxyl radical by the participation of transition metals. Glutathione (GSH) in mitochondria is the only defense available to metabolize hydrogen peroxide. A small fraction of the total cellular pool of GSH is sequestered in mitochondria by the action of a carrier that transports GSH from cytosol to the mitochondrial matrix. Recent evidence position mitochondria as subcellular targets of cytokines leading to overproduction of ROS induced by ceramide, a lipid intermediate of cytokine action. Chronic ethanol-fed cells are selectively depleted of GSH in mitochondria due to a defective operation of the carrier responsible for the transport of GSH from cytosol into the mitochondrial matrix. Its limitation sensitizes alcohol hepatocytes to the prooxidant effects of cytokines and prooxidants generated by the oxidative metabolism of ethanol. One of the mechanisms leading to the onset of selective defect in the mitochondrial transport of GSH induced by chronic ethanol exposure is mediated by decreased fluidity of the mitochondrial inner membrane. Its fluidization by SAM treatment normalizes the steady state levels of GSH in mitochondria contributing to withstand the oxidative stress derived by the oxidative metabolism of ethanol.

[Neuroradiological findings in 2 cases of Wilson disease with neurological involvement]

Wilson disease is an inborn error of copper metabolism that has neurological and hepatic manifestations. We report a 13 years old girl and a 12 years old boy with Wilson disease. In both patient, brain computed tomography and magnetic resonance imaging showed marked involvement of basal ganglia and other deep gray nuclei. Considering that this is a treatable disease, it should be included in the differential diagnosis of the so called "striatal necrosis of childhood".

Tumor necrosis factor increases hepatocellular glutathione by transcriptional regulation of the heavy subunit chain of gamma-glutamylcysteine synthetase

Tumor necrosis factor (TNF) is an inflammatory cytokine that causes cell injury by generation of oxidative stress. Since glutathione (GSH) is a key cellular antioxidant that detoxifies reactive oxygen species, the purpose of our work was to examine the regulation of cellular GSH, the expression of heavy subunit chain of gamma-glutamylcysteine synthetase (gamma-GCS-HS), and control of intracellular generation of reactive oxygen species in cultured rat hepatocytes treated with TNF. Exposure of cells to TNF (10,000 units/ml) resulted in depletion of cellular GSH levels (50-70%) and overproduction of hydrogen peroxide (2-3-fold) and lipid peroxidation. However, cells treated with lower doses of TNF (250-500 units/ml) exhibited increased levels of GSH (60-80% over control). TNF treatment increased (70-100%) the levels of gamma-GCS-HS mRNA, the catalytic subunit of the regulating enzyme in GSH biosynthesis. Furthermore, intact nuclei isolated from hepatocytes treated with TNF transcribed the gamma-GCS-HS gene to a greater extent than control cells, indicating that TNF regulates gamma-GCS-HS at the transcriptional level. The capacity to synthesize GSH de novo determined in cell-free extracts incubated with GSH precursors was greater (50-70%) in hepatocytes that were treated with TNF; however, the activity of GSH synthetase remained unaltered by TNF treatment indicating that TNF selectively increased the activity of gamma-GCS. Despite activation of nuclear factor-kappaB (NF-kappaB) by TNF, this transcription factor was not required for TNF-induced transcription of gamma-GCS-HS as revealed by deletion constructs of the gamma-GCS-HS promoter subcloned in a chloramphenicol acetyltransferase reporter vector and transfected into HepG2 cells. In contrast, a construct containing AP-1 like/metal response regulatory elements increased chloramphenicol acetyltransferase activity upon exposure to TNF. Thus, TNF increases hepatocellular GSH levels by transcriptional regulation of gamma-GCS-HS gene, probably through AP-1/metal response element-like binding site(s) in its promoter, which may constitute a protective mechanism in the control of oxidative stress induced by inflammatory cytokines.

Chromosome markers and alterations in mitotic cells from interspecific Citrus somatic hybrids analysed by fluorochrome staining

Mitotic cells from Rough lemon (Citrus jambhiri Lush.), Ohta ponkan (C. reticulata Blanco) and two somatic hybrid plants obtained from protoplast fusion were analysed by double staining with chromomycin A₃ (CMA) and 4'-6-diamidino-2-phenylindole. Only CMA-positive bands were observed in metaphasic chromosomes. The two parental karyotypes (2n=2x=18) were heteromorphic, yielding some marker chromosomes that could be identified in the somatic hybrids. One of the somatic hybrids had 2n=37 chromosomes, and the possible extra chromosome was distinguishable. The second somatic hybrid was tetraploid (2n=4x=36), with one of the chromosomes bearing a putative structural alteration. Furthermore, aneusomaty and some mitotic abnormalities were also observed in this latter plant. Such irregularities are reported for the first time for citrus somatic hybrids, and their possible causes and implications are discussed.

Aging and detoxifying enzymes responses to hypoxic or hyperoxic treatment

We studied the levels of antioxidant and detoxifying enzymes in the livers and lungs of young and old rats kept under hypoxic or hyperoxic conditions as models of oxidative stress. In particular, we investigated the levels of enzymes directly involved in active oxygen species scavenging (superoxide dismutase, catalase and glutathione peroxidase-selenium dependent) and enzymes challenged with detoxification processes (glutathione transferase, glyoxalase I and glutathione reductase) in order to obtain a wide comparative view of the defence strategies used with respect to the age of the animals. The results show that the responses of some protective enzymes in young rats are opposite to those of old ones. Some of the changes found appear mainly due to age, while others appear to be due only to the oxygen tensions and are independent of the aging process. The glutathione contents of the liver and lung from young and old rats under hypoxic and hyperoxic conditions were measured.

Biochemical basis for glucose-induced inhibition of malolactic fermentation in Leuconostoc oenos

The sugar-induced inhibition of malolactic fermentation in cell suspensions of Leuconostoc oenos, recently reclassified as Oenococcus oeni (L. M. T. Dicks, F. Dellaglio, and M. D. Collins, Int. J. Syst. Bacteriol. 45:395-397, 1995) was investigated by in vivo and in vitro nuclear magnetic resonance (NMR) spectroscopy and manometric techniques. At 2 mM, glucose inhibited malolactic fermentation by 50%, and at 5 mM or higher it caused a maximum inhibitory effect of ca. 70%. Galactose, trehalose, maltose, and mannose caused inhibitory effects similar to that observed with glucose, but ribose and 2-deoxyglucose did not affect the rate of malolactic activity. The addition of fructose or citrate completely relieved the glucose-induced inhibition. Glucose was not catabolized by permeabilized cells, and inhibition of malolactic fermentation was not observed under these conditions. 31P NMR analysis of perchloric acid extracts of cells obtained during glucose-malate cometabolism showed high intracellular concentrations of glucose-6-phosphate, 6-phosphogluconate, and glycerol-3-phosphate. Glucose-6-phosphate, 6-phosphogluconate, and NAD(P)H inhibited the malolactic activity in permeabilized cells or cell extracts, whereas NADP+ had no inhibitory effect. The purified malolactic enzyme was strongly inhibited by NADH, whereas all the other above-mentioned metabolites exerted no inhibitory effect, showing that NADH was responsible for the inhibition of malolactic activity in vivo. The concentration of NADH required to inhibit the activity of the malolactic enzyme by 50% was ca. 25 microM. The data provide a coherent biochemical basis to understand the glucose-induced inhibition of malolactic fermentation in L. oenos.

Sister chromatid exchange (SCE) rates in human melanoma cells as an index of mutagenesis

Melanomas are highly clonogenic. Genetic variability and polymorphism of tumour cell populations have been reported. However, no direct evidence of mutator activity as a source of genetic polymorphism for melanoma cells has been described. Some intermediates of melanin synthesis are cytotoxic and genotoxic and their mutagenic power has been described. We show here that the rate of sister chromatid exchange (SCE) of the line of human melanoma cells used varies with the concentration of the melanin precursor L-tyrosine, in the culture medium. An increase of melanin synthesis results in increased SCE rates. The highest values of SCEs are found in melanotic melanoma cells compared with the amelanotic ones. Indeed we present evidence that melanoma cells show higher levels of SCE when compared with normal human lymphocytes, and to the SCE frequencies derived from the literature on the lymphocytes of familial malignant melanoma, sporadic malignant melanoma patients and the lymphocytes of relatives of familial and sporadic melanoma patients.

GSH transport in mitochondria: defense against TNF-induced oxidative stress and alcohol-induced defect

Mitochondria generate reactive oxygen species (ROS) as byproducts of molecular oxygen consumption in the electron transport chain. Most cellular oxygen is consumed in the cytochrome-c oxidase complex of the respiratory chain, which does not generate reactive species. The ubiquinone pool of complex III of respiration is the major site within the respiratory chain that generates superoxide anion as a result of a single electron transfer to molecular oxygen. Superoxide anion and hydrogen peroxide, derived from the former by superoxide dismutase, are precursor of hydroxyl radical through the participation of transition metals. Glutathione (GSH) in mitochondria is the only defense available to metabolize hydrogen peroxide. A small fraction of the total cellular GSH pool is sequestered in mitochondria by the action of a carrier that transports GSH from the cytosol to the mitochondrial matrix. Mitochondria are not only one of the main cellular sources of ROS, they also are a key target of ROS. Mitochondria are subcellular targets of cytokines, especially tumor necrosis factor (TNF); depletion of GSH in this organelle renders the cell more susceptible to oxidative stress originating in mitochondria. Ceramide generated during TNF signaling leads to increased production of ROS in mitochondria. Chronic ethanol-fed hepatocytes are selectively depleted of GSH in mitochondria due to a defective operation of the carrier responsible for transport of GSH from the cytosol into the mitochondrial matrix. Under these conditions, limitation of the mitochondrial GSH pool represents a critical contributory factor that sensitizes alcoholic hepatocytes to the prooxidant effects of cytokines and prooxidants generated by oxidative metabolism of ethanol. S-adenosyl-L-methionine prevents development of the ethanol-induced defect. The mitochondrial GSH carrier has been functionally expressed in Xenopus laevis oocytes microinjected with mRNA from rat liver. This critical carrier displays functional characteristics distinct from other plasma membrane GSH carriers, such as its ATP dependency, inhibitor specificity, and the size class of mRNA that encode the corresponding carrier, suggesting that the mitochondrial carrier of GSH is a gene product distinct from the plasma membrane transporters.

Changes in histone synthesis and modification at the beginning of mouse development correlate with the establishment of chromatin mediated repression of transcription

The transition from a late 1-cell mouse embryo to a 4-cell embryo, the period when zygotic gene expression begins, is accompanied by an increasing ability to repress the activities of promoters and replication origins. Since this repression can be relieved by either butyrate or enhancers, it appears to be mediated through chromatin structure. Here we identify changes in the synthesis and modification of chromatin bound histones that are consistent with this hypothesis. Oocytes, which can repress promoter activity, synthesized a full complement of histones, and histone synthesis up to the early 2-cell stage originated from mRNA inherited from the oocyte. However, while histones H3 and H4 continued to be synthesized in early 1-cell embryos, synthesis of histones H2A, H2B and H1 (proteins required for chromatin condensation) was delayed until the late 1-cell stage, reaching their maximum rate in early 2-cell embryos. Moreover, histone H4 in both 1-cell and 2-cell embryos was predominantly diacetylated (a modification that facilitates transcription). Deacetylation towards the unacetylated and monoacetylated H4 population in fibroblasts began at the late 2-cell to 4-cell stage. Arresting development at the beginning of S-phase in 1-cell embryos prevented both the appearance of chromatin-mediated repression of transcription in paternal pronuclei and synthesis of new histones. These changes correlated with the establishment of chromatin-mediated repression during formation of a 2-cell embryo, and the increase in repression from the 2-cell to 4-cell stage as linker histone H1 accumulates and core histones are deacetylated.

Comparative analysis on the distribution of heterochromatin in Citrus, Poncirus and Fortunella chromosomes

Double fluorochrome staining with chromomycin A3 (CMA) and 4'-6-diamidino-2-phenylindole (DAPI) was used to characterize and compare the distribution of constitutive heterochromatin along chromosomes of Citrus, Poncirus and Fortunella species. Only CMA-positive bands were distinguishable in metaphase chromosomes. Preferential distribution of heterochromatin in terminal regions, mainly of the long arm, and centromeric regions of a few long chromosomes was a common feature of these genera. Heteromorphism between possible homologous chromosomes was present in the majority of species. Citrus and Poncirus revealed some remarkably uniform chromosomes without any intensively fluorescing region, whereas Fortunella cultivars were differentiated by the presence of CMA bands in all chromosomes. Through measurements assisted by a computer, amounts of CMA-positive regions were shown to be highest in Fortunella. Similarities between Citrus and Poncirus suggest little heterochromatin diversification among karyotypes of these genera, whereas Fortunella, with higher amounts and more homogenous distribution of heterochromatin, is more divergent.