The ultrastructure and argentophilic properties of the nucleolus organizer and centromeric regions of the chromosomes in early mouse embryogenesis

The Ag-staining of metaphase chromosomes in one-cell mouse embryos shows that the nucleolus organizer regions (NORs) are Ag-negative, whereas centromeric regions (CRs) are Ag-positive. Starting from 8-16-cell embryos, NORs stained by AgNO3 constantly, CRs remaining argentophobic. On the ultrathin sections of multicell embryos, Ag(+)-NORs differ from the chromosomal arms: they consist of loosely filaments about 6-8 nm in diameter, characterized by a low electron density. On the contrary, at one-cell stage Ag(-)-NORs are not morphologically identified: chromosomal bodies consist of uniform DNP-fibrils about 20 nm in diameter. These data permit to suppose that extended rDNA may form supranucleosomal and nucleosomal DNP-fibrils in the absence of Ag-proteins. The Ag(+)- and Ag(-)-CRs contain 10-20 nm DNP-fibrils mainly, although their density at multicell stages is higher than in one-cell mouse embryos.     

Changes in the chondriome during the cell cycle of a tissue culture of embryonic pig kidney

The regular cyclic changes of number, size, shape and ultrastructure of cells mitochondria during G1, S, G2-periods and mitosis have been shown by morphometric methods on nonsynchronized culture of PEK tissue. Number of mitochondria is equal in G1 and S cells. Middle size and unbranched mitochondria prevail in G1-period, middle size and large organellae of complicated shape are characteristic for S-period. In G2-period number of mitochondria increases in 1,5 times. Simultaneously the portion of middle and small unbranched mitochondria increases and number of large organellae of complicated shape decreases. Number of mitochondria in mitotic cells in comparison with cells of G2-period does not change distinctly. Most mitochondria are middle and small size, usually unbranched in this period. Considerable increase of mitochondria number in G2-period is probably due to division of the branched mitochondria characteristic for the previous S-period. The mitochondria ultrastructure does not undergo marked changes during the interphase of the cell-cycle and characterizes by prevailing of the orthodox forms of mitochondria: in late G2-period and in the process of mitosis the most mitochondria become condensed.     

Action of actinomycin D on Euglena gracilis ultrastructure

Effects of 1 and 10 mkg/ml concentrations of actinomycin D, an inhibitor of RNA synthesis, on the ultrastructure of a phytoflagellate Euglena gracilis were followed during 48 hours. Similar changes were observed with both the concentrations, but the effect of the higher dose appeared in a short time and was more expressed. The effect of actinomycin D becomes obvious as early as half an hour after its adding; the cell nucleus, chloroplasts and mitochondria show definite responses. Chromatin condensation is seen in the nucleus, the nucleolus is enlarged in size, compressed and fragmented. Chloroplasts react to the action of actinomycin D by swelling, accumulation of osmiophilic globuli, disorganization and reduction of lamellar systems, formation of the myelin figures and gran-like structures and by the decomposition of pyrenoid. The mitochondrial matrix is compressed, the structure and orientation of the cristae become abnormal, and some electron-dense bodies appear.     

Disruption of organization of mitotic microtubules in root meristem cells of Allium cepa induced by chloral hydrate

Data are presented on the effect of chlorahydrate on microtubule organization in the root meristem of Allium cepa. Our studies show that an incomplete preprophase band commonly appears during G2-prophase transition, yet the major effect is the lack of perinuclear microtubules, leading to inhibition of the prophase spindle formation and transition to C-mitosis. Upon chloralhydrate treatment of metaphase cells, we found cells with chromosomes regularly aligned within the metaphase plate and differently disorganized mitotic spindles. Concurrently, C-metaphase cells with remnants of kinetochore fibers were present. In addition, normal bipolar and abnormal irregular types of chromosome segregation were detected, this representing multipolar and diffuse anaphases. The major difference between them is the presence of polar microtubules during multipolar anaphase, and their lacking during diffuse anaphase. Alternatively, microtubule clusters between segregated groups of chromosomes are typical for cells with diffuse anaphase. During bipolar anaphase, excessive aster-like microtubules emanate from the spindle poles, and in telophase accessory phragmoplasts are observed at the cell periphery. The formation of incomplete phragmoplasts was observed after normal bipolar and abnormal chromosome segregation. We conclude that chloralhydrate may affect the nuclear surface capability to initiate the growth of perinuclear microtubules, thus blocking the prophase spindle formation. It also disturbs the spatial interaction between microtubules, which is crucial for the formation and functioning of various microtubular systems (preprophase band, spindle and phragmoplast).     

Ultrastructure and morphology of the mitochondriome of cardiomyocytes from invertebrates. I. The mitochondriome of cardiomyocytes from insects

The cardiomyocyte mitochondrial ultrastructure of two insect species (the American cockroach Periplaneta americana, and a dragonfly Aeschna sp.) has been studied. Mitochondria in cardiomyocytes of these insects are connected by intermitochondrial contacts, similar in morphology to vertebrate intermitochondrial contacts. The number of intermitochondrial contacts differs in cardiomyocytes of the studied insects, numbering 12 and 18 per 100 mitochondria in cardiomyocytes of the cockroach and dragonfly, respectively, which is due presumably to differences in activity of these insects. Cardiomyocytes of both species have several features in common. It was shown that cross-striated myofibrils oriented in different directions occupy 50-58% of the cytoplasmic volume, while mitochondria cover only 16-18%. The pattern of mitochondrial localization differs in cardiomyocytes of the two studied insects. In the cockroach, cardiomyocyte mitochondria are seen both in the center of the cell and on its periphery, in protrusions; whereas in the dragonfly, mitochondria of cardiomyocytes are confined to the protrusions of the abluminal cell side. Mitochondrial profiles are small, their packing is not dense. Mitochondria in cardiomyocytes of these insects have few plastic cristae and dense matrix.     

Experimental Visualization of Chromoneme as a Higher Level of Chromatin Compactization in the Mitotic Chromosome

We succeeded to visualize the chromoneme or a filamentous chromatin structure, with the mean thickness 0.1–0.2 μm, as a higher level of chromatin compactization in animal and plant cells at different stages of chromosome condensation at mitotic prophase and during chromatid decondensation at telophase. Under the natural conditions, chromoneme elements are not detected in the most condensed chromatin of metaphase chromosomes on ultrathin sections. We studied the ultrastructure and behavior of the chromatin of mitotic chromosomes in situ in cultured mouse L-197 cells under the conditions selectively demonstrating the chromoneme structure of the mitotic chromosomes in the presence of Ca²⁺. Loosely packaged dense chromatin bands, ca. 100 nm in diameter, chromonemes, were detected in chromosome arms in a solution containing 3 mM CaCl₂. When transferred in a hypotonic solution containing 10 mM tris-HCl, these chromosomes swelled, lost the chromoneme level of structure, and rapidly transformed in loose aggregates of elementary DNP fibrils, 30 nm in diameter. After this decondensation in the low ionic strength solution, the chromoneme structure of mitotic chromosomes was restored when they were transferred in a Ca₂₊ containing solution. The morphological characteristics of the chromoneme and pattern of its packaging in the chromosome were preserved. However, when the mitotic cells with chromosomes, in which the chromoneme structure was visualized with the help of 3 mM CaCl₂, were treated with a photosensitizer, ethidium bromide, and illuminate with a light with the wavelength 460 nm, chromatic decondensation under the hypotonic solution was not observed. The chromoneme elements in a stabilized chromatin of the mitotic chromosome preserved specific interconnection and the general pattern of their packaging in the chromatid was also preserved. The chromoneme elements in the chromosomes stabilized by light preserved their density and diameter even in a 0.6 M NaCl solution, which normally leads to chromoneme destruction. An even more rigid treatment of the stabilized chromosomes with a 2 M NaCl solution, which normally fully decondenses the chromosomes, made it possible to detect a 3D reticular skeleton devoid of any axial structures. __________ Translated from Ontogenez, Vol. 36, No. 5, 2005, pp. 323–332. Original Russian Text Copyright ? 2005 by Burakov, Tvorogova, Chentsov.     

Protective effect of peptide semax the rat heart in acute myocardial infarction

Semax, a member of ACTH-derived peptides family, has been employed in the treatment of acute ischemic stroke in patients. It decreased neurological deficit and reduced NO hyperproduction in the rat brain, caused by acute cerebral hypoperfusion. We suggested that semax is also able to protect rat heart from ischemic damage in acute myocardial infaction (AMI). AMI was induced by left coronary artery occlusion, myocardial ischemic area averaged 30 % of left ventricle. In 2 hours after coronary occlusion, the AMI group developed 11 % reduced mean arterial blood pressure and 48 % increased diastolic blood pressure in left ventricle in comparison with sham-operated control group. However, infusion of either dobutamine, which directly stimulates myocardial contractility, or sodium nitroprusside and phenylephrine, that change vascular resistance and thus cardiac afterload, did not reveal distinctions in hemodynamic parameters between groups. These data indicate absense or only moderate cardiac dysfunction in rats with AMI and are consistent wih morphometrical and histochemical studies that did not detect any necrotic or apoptotic (TUNEL-test) changes in left ventricular cardiomyocytes in spite of development of distinct ischemic disturbances of mitochondria and nuclear in about 50 % of cardiomyocytes in 2 hours after AMI. Semax (150 microg/kg), given i. p. 15 min and 2 hours after coronary occlusion, caused no effect on cardiac function, but completely prevented ischemia-induced ultrastructural changes of cardiomyocytes. This protective effect was accompanied by the ability of peptide to blunt the increase in plasma concentrations of nitrates, observed in AMI group.