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S Dimitrov

Publications and source records attributed to S Dimitrov.

At least 55 records · Page 3Linked to original sources
PubMed1994

Specific regulation of Xenopus chromosomal 5S rRNA gene transcription in vivo by histone H1.

The incorporation of histone H1 into chromatin during embryogenesis directs the specific repression of the Xenopus oocyte 5S rRNA genes. An increase in histone H1 content specifically restricts TFIIIA-activated transcription, and a decrease in histone H1 within chromatin facilitates the activation of the oocyte 5S rRNA genes by TFIIIA. Variation in the amount of histone H1 in chromatin does not significantly influence somatic 5S rRNA gene transcription. Thus, the regulated expression of histone H1 during Xenopus development has a specific and dominant role in mediating the differential expression of the oocyte and somatic 5S rRNA genes. This example demonstrates that histones can exert dominant repressive effects on the transcription of a gene in vivo in spite of an abundance of transcription factors for that gene.

Animals↗
PubMed1994

Histone acetylation influences both gene expression and development of Xenopus laevis.

We examine the potential role of histone hyperacetylation in gene activation during Xenopus development using Trichostatin A, (TSA), a specific inhibitor of histone deacetylase. We find that TSA is very effective in inducing both core histone hyperacetylation and histone H1(0) gene expression in a Xenopus somatic cell line. In contrast, TSA does not induce histone hyperacetylation or histone H1(0) transcription in Xenopus oocytes. Histone hyperacetylation is developmentally regulated during Xenopus embryogenesis; hyperacetylated histones first accumulate early in gastrulation. The capacity of TSA to induce histone H1(0) gene expression correlates with the induction of histone hyperacetylation. Concentrations of TSA sufficient to induce histone hyperacetylation in Xenopus embryos delay gastrulation and cause diminished midtrunk and posterior formation, suggesting defects in mesoderm formation. Although the constitutive hyperacetylation of the histones does not prevent either the cell division or differentiation sufficient for early morphogenesis it has a role in establishing stable states of differential gene activity during gastrulation.

Acetylation↗
PubMed1994

Remodeling sperm chromatin in Xenopus laevis egg extracts: the role of core histone phosphorylation and linker histone B4 in chromatin assembly.

We find that the remodeling of the condensed Xenopus laevis sperm nucleus into the paternal pronucleus in egg extracts is associated with phosphorylation of the core histones H2A, H2A.X and H4, and uptake of a linker histone B4 and a HMG 2 protein. Histone B4 is required for the assembly of chromatosome structures in the pronucleus. However neither B4 nor core histone phosphorylation are required for the assembly of spaced nucleosomal arrays. We suggest that the spacing of nucleosomal arrays is determined by interaction between adjacent histone octamers under physiological assembly conditions.

Animals↗
PubMed1993

Chromatin transitions during early Xenopus embryogenesis: changes in histone H4 acetylation and in linker histone type.

We describe major transitions in the type and modification of chromatin-associated proteins during the early development of Xenopus laevis. Histone H4 is stored in the diacetylated form in the egg and is progressively deacetylated during normal development. If histone deacetylases are inhibited with sodium butyrate, hyperacetylated histone H4 only accumulates after the mid-blastula transition. The type of linker histone in chromatin also changes during embryogenesis, from predominantly the B4 protein at the mid-blastula transition to predominantly histone H1 at the end of gastrulation. These transitions in chromatin composition correlate with major changes in the replicative and transcriptional activity of embryonic nuclei.

Acetylation↗
PubMed1990

Histones H1 and H4 are present near the replication fork.

The presence of histones H1 and H4 at the sites of actual DNA synthesis has been studied with Ehrlich ascites tumour cells, pulse labeled for different times with 3H-thymidine and then treated with formaldehyde to crosslink histones to DNA. The fixed chromatin fragments were sonicated to reduce the size of DNA, purified in a CsCl gradient and immunoprecipitated with antibodies to histones H1 and H4. Determination of specific radioactivity in precipitated probes showed that both histones have been associated with nascent DNA even upon 1 min pulse with 3H-thymidine, thus indicating their presence near the replication fork.

Animals↗
PubMed1990

[The value of the electrocardiographic indices of left-ventricular hypertrophy for the approximation of the valvular systolic gradient in patients with aortic stenosis].

In 36 patients with mild, moderate and severe aortic stenosis, proved by cardiac catheterization, some electrocardiographic indices for left ventricular hypertrophy were compared with the value of the aortic valve peak systolic gradient. The correlative analysis showed a moderate correlation between the T wave amplitude in leads V5 and V6 of the ECG and the aortic valve gradient--r = 0.46 (p less than 0.005). On the basis of this linear correlation a regression equalization is proposed for the approximate electrocardiographic assessment of the degree of aortic stenosis.

Adult↗
PubMed1989

[CT tomography of normal parotid and mandibular salivary glands].

Computed tomography (CT) allows the differentiation of tissues by measurement of their roentgenologic densities. There are a few controversial literature data on the roentgenologic densities of the parotid and submandibular glands. These differences are, in our opinion, due to several factors: 1. The complex anatomic structure of the facial region of the skull, that demands an exact centering. In daily practice the respective imaging parameters are not always kept constant (including partial volume effects), thus introducing density errors. 2. Metallic prostheses and obturators as well as the high-density bones of the facial skull cause artefacts that impair image quality and density measurements. 3. The small density differences between the salivary glands and the adjacent soft tissues makes their differentiation difficult. 4. Different devices and parameters are used for scanning, resulting in different densities. Considering these facts, we have devised a complex method for the investigation of the parotid and mandibular salivary glands.

Adolescent↗
PubMed1986

Structure of hyperacetylated chromatin: light scattering and flow linear dichroism study.

Cation-induced folding of 10 nm chromatin filament to 30 nm fiber was studied with hyperacetylated chromatin using light scattering at 90 degrees and flow linear dichroism. Acetylated chromatin folded in a way indistinguishable from that of the control chromatin: both the compactness of chromatin and the orientation of nucleosomes relative to the fiber axis were identical at a given salt concentration.

Acetylation↗
PubMed1986

Electron microscopic and enzyme investigations of the testicular tissue in infertile males.

The ultrastructural characteristics of the testicular tissue in male infertility and the isoenzyme spectrum of some enzymes in sperm cells have been studied. The testicular material was taken by Vilar's method from three healthy males with normospermia and eleven males with hypogonadism, azoospermia and infertility. The material was treated by the routine methods for electron investigation and the observations were done with an electron microscope Opton EM 109. Horizontal electrophoresis of the testicular homogenate was done according to Nance. Malate dehydrogenetic activity (MDX) was rendered according to the method of Shaw and Prasad, and diaphoresis (DP) was carried out according to Brewer. It was found that spermatogenesis was interrupted at the pachytene stage at an ultrastructural level. Biochemical investigations showed that in the infertile testis two other atypical fractions appeared on diaphoresis, while at the malate dehydrogenase, a second fraction had considerably lower intensity as compared to the controls. It is pointed out that some profound disorders developing in the infertile testis affect mainly the germinal cells, which was proved at the ultrastructural level and also by the analysis of the isoenzymes MDH and DF key enzymes of carbohydrate metabolism.

Humans↗
PubMed1985

A triple helix model for the structure of chromatin fiber.

A model of chromatin fiber structure is presented in which a repeating unit of a trinucleosome forms a 3-dimensional zigzag. Twisting and compression of the zigzag result in a triple helix structure. The model is built mainly on the flow linear dichroism data showing that nucleosomal disc faces are tilted relative to the fiber axis, the orientation of nucleosomes does not change upon folding and unfolding of chromatin, and the orientation of nucleosomes is maintained by the globular domain of histone H1.

Animals↗
PubMed1984

[Pharmacological and clinico-pharmacological studies of diazepam powder in suspensions].

Studied was the preparation diazepam-pulvis for suspension (DPS) with regard to its tranquillizing and myorelaxing doses, inhibiting the aggression, and preventing the stress conditions in domestic animals and birds. It was established that at oral application to pigs at rates of 1 to 2 mg/kg body mass DPS produced a pronounced tranquillizing effect, while at 3 mg/kg it led to myorelaxation as well. In sheep tranquillizing effect was seen when amounts of 3 to 5 mg/kg body mass were used, and myorelaxation was achieved with 6.6 to 13.2 mg/kg. In male calves tranquillization was manifested after doses of 3 mg/kg body mass were applied. In hens the tranquillizing dose was found to be 3 mg/kg body mass, and the myorelaxing one--4 mg/kg; in cocks the respective doses were 5 and 7 mg/kg body mass. At the rate of 3 mg/kg body mass DPS was found to enhance the thiopental-sodium narcosis. When offered to pigs at 2 mg/kg body mass in admixture with the feed DPS led to tranquillization and suppression of the active and passive defense response. No full prevention of cannibalism could be achieved. The daily administration in the course of 30 days with the ration of bull-calves at the rate of 3 mg/kg body mass was shown to calm the animals under loose housing in boxes and affect favourably their weight gain. Admixed with the feed of cocks at 5 mg/kg DPS suppressed aggressiveness.

Adaptation, Physiological↗
PubMed1981

[Toxicity of sodium monensin for pigs].

Studied were the acute and subchronic toxicity of monensin-Na in pigs. The investigations were carried out with elancoban-100, containing 10 per cent monensin-Na. A total of 46 pigs were used, weighing 15 to 60 kg. The preparation was applied individually via the nose or with the feed. It was found that nasally at 5 mg/kg the preparation did not lead to intoxication; rates of 10 and 20 mg/kg proved toxic, and a dose of 30 mg/kg was lethal. Feed containing 300 ppm of monensin-Na given but once led to intoxication and death with part of the animals. Pig tolerated well continuous (33 days) intake of feed that contained the sodium salt of monensin in concentrations of 120 and 240 ppm - no changes in the general status and behaviour were observed, nor were there any deviations in the morphologic and biochemical composition of the blood. It was demonstrated that the low amounts of monensin stimulated the weight gain of pigs. On the other hand, the clinical picture of the intoxication consisted in going off feed, higher pulse and respiration rates, involvement of the nervous system (depression of the nociceptive, eye closure, and ear reflexes, paresis of the hind limbs, and in severe cases - of the forelimbs too), hematuria in most of the animals, higher SGPT activity, and delayed ESR. Morphologically, there were vascular and slightly manifested degenerative changes in the parenchymal organs, red to brown urine in the bladder, strongly enlarged gallbladder, and catarrhal and hemorrhagic gastroenteritis. Histologically, there was granular and fatty degeneration of the kidneys, liver, and heart, hyperemia, perivascular and pericellular edema and degenerative changes in the glial cells of the berebrum, cerebellum, and medulla oblongata.

Animal Feed↗