On mechanisms of antitumor action of tropolon series compounds

The review provides information on the mechanisms of the antitumor action of natural and synthetic compounds of the tropolone series, obtained over the past 30 years in studies on cell cultures and, to a lesser extent, in in vivo experiments. Interest in this group of substances is due to the urgent need of clinical oncology for drugs that effectively damage malignant cells and, at the same time, are safe for healthy tissues. The processes that realize the effects of colchicine, hinokithiol (ß-tuyaplicin) and some of their derivatives (derivatives of bistropolone, α-substituted tropolones, etc.) have been studied most fully. Herewith, more numerous mechanisms of realization of the antitumor effect of hinokithiol and its derivatives were revealed in comparison with colchicine. In addition to the disruption in the formation of the cell division spindle, shown for colchicine and colchamine, such phenomena as caspase-dependent apoptosis and some other types of apoptosis, autophagy, limitation of mitochondrial metabolism, DNA damage and demethylation, and accelerated aging of malignant cells etc. have been described. The promising properties of 2‑quinolyl 1,3‑tropolone derivatives have been shown, and the relationship of their antitumor effect with the induction of apoptosis and changes in the activity of the ERK signaling pathway in some types of malignant cells have been revealed. The results indicate a multiplicity of possible ways of the influence of tropolones on the state of malignant cells, the conditions for the implementation of ones need to be clarified, especially with a lack of information about in vivo processes.The review includes information from the literature presented in the Scopus, WoS, Pubmed databases. 35 % of articles have been published in the last 5 years.

THE CYTOLOGICAL AND CYTOGENETIC STUDY OF THE ALTERNATED FORMS OF ALFALFA

Colchicine in experimental mutagenesis is used to induce polyploidy, since it, by destroying the division spindle, prevents chromosomes from separating. The importance of studying the mutagenic effect of colchicine on a plant cell is also determined by the practical application of colchicine in the enrichment of plant genetic resources of plants, the creation of cytogenetic collections and their use in breeding programs. In our experiments, we studied the effect of colchicine on alfalfa and the effect of its influence. Seeds of varieties ASKHI-1 and AzNIKHI-262 obtained as a result of treatment with different concentrations of colchicine (0.02% and 0.04%) were used as plant material. In some anaphases, chromosome delays were observed when diverging to the poles. No cells with a doubled set of chromosomes were found. According to the results of studying the stages of mitosis, it should be noted that ASKHI-1 variety is more sensitive to colchicine treatment than AzNIKhI-252, since the first variety showed significantly greater deviations from the control and another variety at the stage of mitotic activity.

Microsporogenesis and pollen formation in Larch Sukachev (Larix Sukaczewii Djil.) on permanent forest seed plot in Semiluksky forestry

The formation of male and female generative buds in the Sukachev larch in the conditions of Voronezh in the second decade of August is considered. The behavior of chromosomes in the meta-, ana -, and telophase of the first and second divisions of meiosis is analyzed. In each phase, 150–200 microsporocytes were taken into account. According to the results of the conducted studies, it was revealed that the microsporogenesis of larch proceeded asynchronously. A significant proportion of the disorders are caused by chromosome lag and the formation of bridges, the formation of a hexad, and the release of chromosomes outside the division spindle. The viability of Sukachev larch pollen is estimated to be high. A small number of disturbances in the process of meiotic divisions and the formation of gametophytes did not lead to the formation of a significant amount of sterile pollen. The average pollen size varies between 82.18–86.4 microns. Pollen has a spherical shape

Augmin regulates kinetochore tension and spatial arrangement of spindle microtubules by nucleating bridging fibers

ABSTRACTThe mitotic spindle functions as a molecular micromachine that evenly distributes chromosomes into two daughter cells during cell division. Spindle microtubules in human cells are mainly nucleated at the centrosome and on the lateral surface of existing microtubules by the augmin complex. However, it is unknown how the augmin-mediated nucleation affects functionally distinct microtubule bundles and consequently the forces within the spindle. Here we show, by using siRNA depletion and CRISPR knock-out of the augmin complex subunits HAUS6 or HAUS8, that augmin is crucial for the nucleation of bridging microtubules, which laterally link sister kinetochore fibers. Augmin depletion resulted in a reduction in the number of microtubules within bridging fibers by around 80% and in kinetochore fibers by 40%, suggesting that the bridging microtubules are mainly nucleated at the surface of present microtubules. In augmin-depleted cells, the interkinetochore distance decreased preferentially for kinetochores that lack a bridging fiber, independently of the thickness of their k-fibers, implying that augmin affects forces on kinetochores largely via bridging fibers. Without augmin the number of bridging fibers decreased, with the remaining ones mostly confined to the spindle periphery with an increased overlap length. A slower poleward flux of microtubules after augmin depletion is indicative of slower sliding within the bridging fiber. Our results demonstrate a critical role of augmin in the formation of bridging microtubules and proper architecture of the metaphase spindle, suggesting a model where sliding of augmin-nucleated bridging microtubules promotes poleward flux of k-fibers and thus tension on kinetochores.

Functional analysis of the microtubule-interacting transcriptome

RNA localization is an important mechanism for achieving precise control of posttranscriptional gene expression. Previously, we demonstrated that a subset of cellular mRNAs copurify with mitotic microtubules in egg extracts of Xenopus laevis. Due to limited genomic sequence information available for X. laevis, we used RNA-seq to comprehensively identify the microtubule-interacting transcriptome of the related frog Xenopus tropicalis. We identified ∼450 mRNAs that showed significant enrichment on microtubules (MT-RNAs). In addition, we demonstrated that the MT-RNAs incenp, xrhamm, and tpx2 associate with spindle microtubules in vivo. MT-RNAs are enriched with transcripts associated with cell division, spindle formation, and chromosome function, demonstrating an overrepresentation of genes involved in mitotic regulation. To test whether uncharacterized MT-RNAs have a functional role in mitosis, we performed RNA interference and discovered that several MT-RNAs are required for normal spindle pole organization and γ-tubulin distribution. Together, these data demonstrate that microtubule association is one mechanism for compartmentalizing functionally related mRNAs within the nucleocytoplasmic space of mitotic cells and suggest that MT-RNAs are likely to contribute to spindle-localized mitotic translation.

The spindle position checkpoint: how to deal with spindle misalignment during asymmetric cell division in budding yeast

During asymmetric cell division, spindle positioning is critical to ensure the unequal segregation of polarity factors and generate daughter cells with different sizes or fates. In budding yeast the boundary between mother and daughter cell resides at the bud neck, where cytokinesis takes place at the end of the cell cycle. Since budding and bud neck formation occur much earlier than bipolar spindle formation, spindle positioning is a finely regulated process. A surveillance device called the SPOC (spindle position checkpoint) oversees this process and delays mitotic exit and cytokinesis until the spindle is properly oriented along the division axis, thus ensuring genome stability.

Establishment of Plastid-Based Quadripolarity in Spore Mother Cells of the moss Funaria Hygrometrica

Development of a tetrad of meiospores is one of the most widespread examples of geometrically precise cell morphogenesis in plants. We have studied the process in the moss Funaria hygrometrica. Changes leading to a quadripolar organization of the prophase spore mother cell (SMC) start in the archesporial cells several cell generations before meiosis. The number of plastids per cell is reduced to two and these play an increasing part in subsequent mitoses and meiosis. During meiotic prophase, the plastids elongate until they enclose the peripheral nucleus. The nucleus is then drawn back into the centre of the cell as the plastids rotate and ultimately assume a mutually perpendicular configuration. The tips of the plastids thus lie at the vertices of a tetrahedron arranged around the nucleus, which itself becomes deformed into a tetrahedral shape. Quadripolarity has now been set up in anticipation of the two meiotic divisions. The first division spindle is also somewhat tetrahedral, with broad poles oriented perpendicular to one another along two opposite edges of the tetrahedron. As a consequence, the daughter nuclei are, from their inception, mutually perpendicular and elongated along the first spindle poles, ready for the second division, which places one haploid nucleus opposite each of the four plastid tips. Simultaneous cytokinesis then bisects the plastids and generates a tetrad of spores. The morphological evidence thus indicates that the plastids are involved in the development of internal quadripolarity in the outwardly apolar SMCs.