[The quantitative study of the areas of active rDNA location and of the other parameters of the interphase nucleolus detectable by silver staining during the cell differentiation of the rat trophoblast]. / Kolichestvennoe issledovanie zon lokalizatsii aktivnosti rDNK i drugikh parametrov interfaznogo iadryshka, vyiavliaemykh metodom serebreniia v khode differentsirovki kletok trofoblasta krysy.

Different quantitative parameters of nucleolar silver staining have been studied in the cambial rat trophoblast cells on the 12th, 13th and 14th days of gestation. It has been shown that the number of Ag-positive granules in the nucleoli varied from 10 to 120. The number and the total area of silver stained granules in the nuclei increased progressively in the course of polyploidization, but was not doubled passing to the next ploidy level. Nevertheless, nucleolar area increased proportionally to the ploidy degree. The mean number and the total area of Ag-stained granules as well as the nucleolar area estimated for each ploidy level did not change significantly in the course of placenta development, suggesting an unchanged level of NOR activity at the studied stages of trophoblast cell differentiation. The data obtained on the interphase nucleoli differ from the data of the analysis of the metaphase Ag-NOR at the same period of placenta development, suggesting a diversity in the interphase and metaphase NOR organization. A proportion of cells with different number of nucleoli in the cambial rat trophoblast cells was maintained unchanged in the studied period of the placenta development, the majority (80-90%) of cells contained from 1 to 3 nucleoli. Such a proportion was similar in the cells of different levels of ploidy up to 16c. In this connection the association of NORs is suggested to be in relation with switching from the polyploid mitotic cycle to the endoreduplication leading to polyteny.

[Cytological research on the argentophilic nucleolus-organizer regions of the metaphase chromosomes in parthenogenetic mouse embryos]. / Tsitologicheskoe issledovanie argentofil'nykh iadryshkoobrazuiushchikh raionov metafaznykh khromosom u partenogeneticheskikh zarodyshei myshei.

Silver staining technique visualizing argentophilic nucleolus organizer regions (Ag-NORs) was used for studying parthenogenetic mouse embryos produced by artificial activation of oocytes in Ca(2+)-Mg(2+)-free medium. Ag-NOR-containing chromosomes were detected in metaphases of parthenogenetic embryos during six successive cleavage divisions starting with the two-cell stage. The frequency of metaphases with varying AG-NOR number in diploid parthenogenones was similar to that in the control (fertilized) embryos. Average number of metaphase Ag-NOR chromosomes (calculated per diploid chromosome set) in haploid parthenogenones exceeded that in the control; in some cases all NORs were stained by silver. This is evidence that latent ribosomal cistrons in some chromosomes can be activated.

[The nucleolus organizer regions of the metaphase chromosomes in cambial cell populations of mouse and rat placenta]. / Iadryshkoobrazuiushchie raiony metafaznykh khromosom v kambial'nykh kletochnykh populiatsiiakh platsenty myshi i krysy.

The number of silver-stained nucleolus organizing regions (Ag-NORs) was counted in metaphase plates of the fetal part of placenta of mice and rats and in the tissues of their embryos. On day 9 of mouse gestation and on day 12 of rat gestation, up to 82% of metaphases in the fetal part of placenta have the highest possible number of chromosomes with Ag-NORs (9-10 for mice and 5-6 for rats). In the later embryogenesis (day 10 for mice and day 14 for rats), a great number of metaphases have either no Ag-NORs (34.9% for mice, 17.9% for rats), or only 1-2 Ag-NOR-chromosomes (17.4% for mice and 14.5% for rats). But in the tissues of embryos being on the same embryonic stages the changes in frequency of metaphases with different numbers of Ag-NOR-chromosomes have proved to be less obvious. In the differentiated polyploid placenta cells the number of chromosomes with Ag-NORs can be considerably lower than in diploid ones. It is proposed that the changes in frequency of metaphases with different numbers of Ag-NOR-chromosomes may reflect the regulation of ribosomal gene transcription in the embryogenesis, in particular, in differentiation of cambial cell populations of rodent placenta.

The silver-stained NOR and argentophilic nuclear proteins in early mouse embryogenesis: a cytological study.

Silver staining (Howell and Black, 1980) was used in light and electron microscopic studies for detecting the localization of argentophilic nuclear proteins in fertilized ova and cleaving mouse embryos. No silver-stained nucleolus organizing regions (NORs) (Ag-NORs) were visualized in the metaphase chromosomes of the first cleavage mitosis. From the 2-cell stage on, metaphase chromosomes contained Ag-NORs. Argentophilic proteins were detected in the pronuclei of the 1-cell embryos, i.e. before transcription of the ribosomal genes started. After fertilization these proteins accumulated on the decondensing sperm chromatin and telophase maternal chromosomes, then migrated into the pronuclei to be stored in pronucleoli, and, during mitosis, were transferred into the cytoplasm. In the metaphase chromosomes of the cleaving embryos Ag-NORs adequately reflected the transcriptional activity of the ribosomal genes, whereas in pronuclei of the 1-cell stage embryos argentophilic proteins were not involved in this process, but are likely to play a part in the formation and maturation of pronucleoli, and in the cell cycle regulation.

[The first cycle of DNA replication in parthenogenetic mouse embryos]. / Izuchenie pervogo tsikla replikatsii DNK u partenogeneticheskikh zarodyshei myshei.

Dynamics of the first cell cycle in parthenogenetic mouse embryos derived from ethanol-activated eggs was studied using 3H-thymidine. DNA synthesis starts within 5 h and is terminated within 10 h after activation: it lasts ca. 6 h. Changes in the intensity of 3H-thymidine incorporation and in the distribution of radioactive label between haploid and diploid parthenogens were observed. 3H-thymidine was shown to incorporate into pronucleoli of diploid parthenogens and late-labeled heterochromatin blocks were bound in both diploid and haploid pronuclei. The structure of the first cell cycle in parthenogenetic and normal embryos is discussed.

[The ultrastructure and argentophilic properties of the nucleolus organizer and centromeric regions of the chromosomes in early mouse embryogenesis]. / Ul'trastruktura i argentofil'nye svoistva iadryshkoobrazuiushchikh i tsentromernykh raionov khromosom v rannem émbriogeneze myshi.

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.

[Cytological research on localizing argentophilic proteins in one-cell mouse embryos]. / Tsilogicheskoe issledovanie lokalizatsii argentofil'nykh belkov u odnokletochnykh zarodyshei myshei.

Localization of argentophilic proteins on mouse one-cell embryos has been studied under light and electron microscope using the silver staining that reveals transcriptionally active nucleolus-organizing chromosome regions (NORs). Although argentophilic proteins are observed in NORs of metaphase chromosomes only after the second cleavage division, they can be detected in nuclear apparatus of one-cell embryos, that is at the stage when ribosomal genes are not yet transcribed. Argentophilic proteins are visualized on the surface of decondensing chromatin of the spermatozoon head and on maternal telophase chromosomes immediately after the fertilization. They migrate into pronuclei and are accumulated in pronucleoli. During mitosis argentophilic proteins bind to chromosomes and move to cytoplasm. The importance of argentophilic proteins at the initial stages of mammalian embryogenesis is discussed.

[Intravital selection of early mouse embryos by sex and karyotypic characteristics]. / Prizhiznennyi otbor rannikh zarodyshei myshei po polu i osobennostiam kariotipa.

The possibility of live karyotyping by a single blastomere isolated at the 2-, 4-, and 8-cell stage has been investigated. It is expedient to use to this end a single blastomere isolated from a 4-cell embryo. Three rest blastomeres formed normal morulae or blastocysts upon cultivation during 44 or 68 hrs. When the isolated blastomeres were cultivated for 14-16 hrs in a medium 0.5 micrograms/ml colcemide, 97% of blastomeres were at the metaphase stage and 72% of chromosome plates were suitable for karyotyping. The prospects of the method proposed in experimental embryology and for selection of the early embryos of farm animals by sex are discussed.