SPATIAL ARRANGEMENT OF MACRO-, MIDI- AND MICROCHROMOSOMES
IN TRANSCRIPTIONALLY ACTIVE NUCLEI OF GROWING OOCYTES IN BIRDS
OF THE ORDER GALLIFORMES
A. V. Maslova, A. V. Krasikova 1
Laboratory of Chromosome Structure and Function, St. Petersburg State University;
1 e-mail: spbchromas@gmail.com
Three-dimensional genome organization in the cell nucleus reflects its functional state and is one of the regulatory levels of gene expression. Thus, a detailed exploration
of the interrelations between the genome spatial organization and functioning is essential. In this work, three-dimensional genome organization in growing oocytes of Galliform
birds, with giant transcriptionally active nucleus characterized by nearly absolute lack of structural constraints on chromosome decondensation, is analyzed in detail. Radial
distribution of three groups of chromosomes with different size and gene density in the nuclei of chicken and Japanese quail oocytes was analyzed using confocal laser
scanning microscopy followed by the 3D-reconstruction. The chromosome position relative to the nuclear center was estimated by analyzing its localization in the certain
radial zones of the nucleus and direct distance measurements from the centre of the nucleus to the terminal regions and the center of gravity of the chromosome. It has been
shown that, in the transcriptionally active nuclei of avian oocytes, chromosomes are located at a significant distance from the nuclear envelope and the gene-rich
microchromosomes have no preferential location close to the center of the nucleus and are localized mainly at the periphery of the region occupied by the whole chromosome
set. Therefore the radial distribution of lampbrush chromosomes in the oocyte nucleus does not obey the regularity of the spatial arrangement of chromosomes in the
interphase nucleus according to which the gene-rich chromosome territories are located at the nuclear center and the gene-poor ones are at the nuclear periphery. With the
help of visualization of 3D-preserved lampbrush chromosomes in the intact nucleus, we have confirmed the presence of the repulsion forces between the lateral loops of
lampbrush half-bivalents and the lack of interactions between the heterochromatic segments of different bivalents at the lampb-rush stage of oogenesis.
Key words: avian oogenesis, cell nucleus, domestic animals, genome architecture, lampbrush chromosomes, telomeres, transcription,
three-dimensional reconstruction
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