Analysis of three-dimensional organization of polytene chromosomes in the nucleus nurse cells Drosophila virilis (Diptera: Drosophilidae)

The problem of the spatial organization of the genome is a key to modern genetics. Currently, a significant role in determining the heterochromatin of the spatial organization of chromosomes in the interphase nucleus is demonstrated. The location of the genetic material in the nucleus space largely determines its transcriptional status. Consequently, the study of the spatial organization of chromosomes and pericentromeric heterochromatin regions in the cell nucleus is an important task. Drosophila species are convenient objects for the study of issues related to the spatial organization of chromosomes in the interphase nucleus because they have large and well-structured polytene chromosomes. It was shown that the study of architecture nucleus in generative cell system is of particular importance. Polytene chromosomes of ovarian nurse cells of D. virilis have a common chromocenter, consisting of α-and β-heterochromatin, as well as in the nuclei of the salivary glands. We identified four morphological types of architectonic nuclei nurse cells in 12 species of virilis group: a local chromocenter, diffuse chromocenter, chromosomes dispersed in the nucleus space and the chromosomes contacting the pericentromeric regions of the chromosomes to the nuclear envelope. These results were obtained on squashed preparations, and therefore they can be measured only by the presence or absence of chromocenter and associations of chromosomes in relation to each other. Therefore, the aim of the present research was to investigate the three-dimensional organization of pericentromeric heterochromatin regions of chromosomes in the nurse cells of D. virilis throughout all stages of polytenization: from primary polytene nuclei with reticular structure to the design of the polytene chromosomes to secondary polytene nuclei with reticular structure. In this connection, there was held microdissection chromocenter of salivary gland polytene chromosomes and established region-specific DNA library (DvirIII). Then, 3D FISH DvirIII with chromatin nurse cells of D. virilis was performed at different stages of polytenization. At the stage of primary reticular nuclei there was revealed brightly colored DAPI block α-heterochromatin, while the β-heterochromatin chromocenter totally marked DvirIII. In the space of the nucleus ft-heterochromatin there is a local area and in close contacts with the block a-heterochromatin. At the stage formed polytene chromosomes DvirIII detected in pericentromeric regions of each chromosome and the telomeric region of chromosome 5. At the stage of secondary reticular nuclei, ft-heterochromatin is located remotely with respect to the block a-heterochromatin and more disperse in nucleus space. Thus, throughout all stages of polytenization a-heterochromatin remains compact and does not detect DNA probe. в-heterochromatin is labeled extensively and shows some of the dynamics in the position in space of the nucleus relative to the a-heterochromatin. 3D FISH DvirIII with chromatin nurse cells of D. virilis allowed to establish that throughout all stages of polytenization chromocenter maintained in the nucleus of nurse cells.

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