The interposition of attachment points of XL and 3R chromosomes on the nuclear envelope in the cells of somatic and generative systems of malarial mosquito Anopheles messeae Fall

The study was supported by the Grant of the President of the Russian Federation МК-4158.2012.4, the Ministry of education and science of Russia, the project 14.B37.21.1116 and the Grant of the Russian Foundation for Basic Research 12-04-31201. The nonrandom position of chromosomes in the nucleus is provided by the attachment of chromosomes to the frame structure, the role of which can be performed by the nuclear lamina. There are two classes of lamina-associated domains in the genome: conservative for all tissues and tissue-specific. Contact formation in various chromosome regions can induce activation or repression of defined gene patterns, specific for each cell line. In this work, we proposed that this process may not only determine the presence or absence of contact of chromosomes with the envelope in certain areas, but also the position of the contacts of chromosomes, relative to each other, on the nuclear envelope. We defined remoteness of points of XL and 3R contacts to the nuclear envelope from each other in the internuclear space of the cells of Anopheles messeae Fall. The localization of regions was performed by 3D FISH of microdissected DNA-probes of 32d and 2b-c regions with intact nuclei of nurse cells, salivary glands cells, follicular epithelium cells and imaginal discs cells. These cells differed from each other by the level of ploidy (polyploidy and diploid cells), by the type of polyteny (classic politene chromosomes cells and cells with cryptic politeny), by the way of differentiation (germ line cells and somatic cells) and by the potential for further development (terminally differentiated and stem cells). The estimation of the distance between points of chromosomes contacts to the nuclear envelope was performed by determining the angle between two imaginary vectors, drawn from the center of the nucleus to the corresponding points of contact. We showed that the interposition of points of contacts for XL and 3R chromosomes is tissue-specific. The main conclusion, made on the basis of the results of this work, lies in the fact that the most significant differences in the spatial interpositions of XL and 3R chromosomes attachment areas are observed in germ-line cells - nurse cells. Thus, we confirmed the special importance of interposition of attachment points of the chromosomes in the cells of the generative system of malarial mosquitoes. Of great interest is the difference of spatial organization of chromosomes of imaginal disc cells from other cells of the somatic system, which indicates the presence of an unusual system of chromosome attachment to the nuclear envelope, perhaps similar to the nurse cells, in the nuclei of these cells. It remains unclear, whether the observed features of these cells are connected with their active division or the ability to further differentiation. Further research will be aimed at clarifying the causes of interstitial differences in the nuclear architecture of chromosomes.

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