Chromosome Migration Research Articles

Analysis of CENP-B Boxes as Anchor of Kinetochores in Centromeres of Human Chromosomes.

The kinetochore is a multiprotein structure that attaches at one end to DNA in the centromere and at the other end to microtubules in the mitotic spindle. By connecting centromere and spindle, the kinetochore controls the migration of chromosomes during cell division. The exact position where the kinetochore assembles on each centromere was uncertain because large sections of centromeric DNA had not been sequenced due to highly repetitive alpha-satellite arrays. Embedded in the arrays is a 17 bp consensus sequence, the so-called CENP-B box, which binds the CENP-B protein, the only protein that binds directly to centromeric DNA. Recently, the Telomere-to-Telomere Consortium published the complete centromeric DNA sequences of all chromosomes including their epigenetic modifications in the T2T-CHM13 map. I used data from the T2T-CHM13 map to locate the CENP-B boxes in the centromeres as anchor of kinetochores. Most of the CENP-B boxes in centromeric DNA are methylated with the exception of the so-called centromere dip region (CDR), where CENP-B protein dimers bind to adjacent unmethylated CENP-B boxes and interact with CENP-A and CENP-C proteins to assemble the kinetochore. The centromeres of all chromosomes combined have a size of 407 Mb of which the kinetochores account for 5.0 Mb or 1.2%. There is no correlation between centromere and kinetochore size (P = .77). While the number of CENP-B boxes varies 4-fold between chromosomes, their density (number/Kb) varies less than 2-fold with a mean of 2.61 ± 0.33. The narrow range ensures a uniform pull of the spindle on the centromeres. I illustrate the findings in a model of the human kinetochore anchored at unmethylated CENP-B boxes in the CDR and present circos plots of chromosomes to show the location of kinetochores in their respective centromeres.

The effects of MEK and PKA inhibition on Spire proteins during oocyte maturation.

Asymmetric division of oocytes driven by chromosome migration is a crucial step of oocyte maturation. Actin filaments take key roles in chromosome migration in oocytesThe aim of this study was to determine the effects of MEK and PKA inhibition on the levels of Spire-1 and Spire-2 proteins that are known to be related to actin nucleation.MEK inhibitor PD98059 and PKA inhibitor H89 were applied during IVM to the oocytes retrieved from preovulatory ovarian follicles of PMSG induced 3-5 weeks old female BalbC mice. GVBD and PBE rates were determined. Spire-1 and Spire-2 proteins were detected by immunofluorescence and western blot in oocytes at different maturation stages.Though GVBD rates were similar in different groups, PBE rates were lower in the MEK inhibition group. Through immunofluorescence, cortical localizations of Spire-1 and Spire-2 were determined. MEK inhibition resulted in a decrease in cortical Spire-1 and Spire-2 levels in PBE oocytes. PKA inhibition led to an increase in cortical Spire-1 levels in spindle migration stage oocytes, and an increase in cortical and total Spire-2 levels in PBE oocytes. Application of both MEK and PKA inhibition resulted in compensation of the decrease in Spire-1, while Spire-2 levels remained low with no compensation of PKA inhibition.According to the results of this study, chemical inhibition of MEK and PKA during oocyte maturation alters Spire-1 and Spire-2 protein levels.

Morphological characterization and cytological studies of the green-stemmed and the red-stemmed Basella alba

Basella alba is an underutilized vegetable with ethnobotanical importance used for culinary as well as medicinal purposes in many parts of the world. Morphological characterization and chromosome studies of the mitotic and meiotic cells of the green stemmed and the red-stemmed B. alba was carried out with a view to filling the knowledge gaps that exist in their morphological characterization and also to provide insightful information on their chromosome numbers and meiotic behaviour. The B. alba accessions studied were characterized with respect to their habit, leaves, inflorescence, fruits and seeds. Mitotic and meiotic studies were carried out on the Basella accessions using standard techniques. The morphological studies revealed significant differences between the green-stemmed and red-stemmed Basella alba with respect to the green/red colour of their stems, colour of the flower bud apex, mean plant height at flower bud initiation, mean leaf length, mean leaf width, mean petiole length, mean flower per spike, mean fruit length and mean fruit diameter. The cytological study revealed a chromosome number of 2n=4x=44 for both the green-stemmed and the red-stemmed B. alba studied. It also revealed the occurrence of chromosomal aberrations such as stickiness and precocious migration of chromosomes to the poles during meiosis, which could lead to irregular chromosome segregation that could result in chromosome instability and aberrant meiotic products within the species.

Microsporogenesis in the triploid hybrid ‘Beilinxiongzhu 1#’ and detection of primary trisomy in 2x × 3 × Populus hybrids

BackgroundPrimary trisomy is a powerful genetic tool in plants. However, trisomy has not been detected in Populus as a model system for tree and woody perennial plant biology.ResultsIn the present study, a backcross between Populus alba × Populus glandulosa ‘YXY 7#’ (2n = 2x = 38) and the triploid hybrid ‘Beilinxiongzhu 1#’ (2n = 3x = 57) based on the observation of microsporogenesis and an evaluation of the variations in pollen was conducted to create primary trisomy. Many abnormalities, such as premature migration of chromosomes, lagging of chromosomes, chromosome bridges, asymmetric separation, micronuclei, and premature cytokinesis, have been detected during meiosis of the triploid hybrid clone ‘Beilinxiongzhu 1#’. However, these abnormal behaviors did not result in completely aborted pollen. The pollen diameter of the triploid hybrid clone ‘Beilinxiongzhu 1#’ is bimodally distributed, which was similar to the chromosomal number of the backcross progeny. A total of 393 progeny were generated. We provide a protocol for determining the number of chromosomes in aneuploid progeny, and 19 distinct simple sequence repeat (SSR) primer pairs covering the entire Populus genome were developed. Primary trisomy 11 and trisomy 17 were detected in the 2x × 3 x hybrid using the SSR molecular markers and counting of somatic chromosomes.ConclusionsNineteen distinct SSR primer pairs for determining chromosomal number in aneuploid individuals were developed, and two Populus trisomies were detected from 2x × 3 x hybrids by SSR markers and somatic chromosome counting. Our findings provide a powerful genetic tool to reveal the function of genes in Populus.

Effects of sexual polyploidization on reproductive development in a full-sib poplar family

Populus is an important source of woody biomass in the Northern Hemisphere. Sexual polyploidization plays a valuable role in the genetic improvement of Populus, resulting in tremendous variation in phenotypic traits. Most studies have focused on the variations in the vegetative growth of allopolyploid Populus; however, variations in the reproductive development of different polyploid genotypes of the progeny remain unclear. In this study, catkin traits, pollen size and viability, meiotic development, and reproductive ability were analyzed based on a full-sib family including diploid and triploid hybrids of (Populus pseudo-simonii × P. nigra ‘Zheyin3#’) × (P. × beijingensis) to understand the effects of sexual polyploidization on reproductive development in Populus hybrids. Catkin traits varied among the genotypes in the full-sib family. A ploidy change resulted in significant variation in male catkin length and male flower number per catkin but not in female catkin traits, suggesting that Populus catkin development may be more sensitive to respond to a change in ploidy level in male plants than in female plants. The male diploid hybrids had significantly smaller pollen grains, but higher pollen germination rates than the triploid hybrids. Giant pollen grains with large diameters were recorded in all-male diploid and triploid hybrids, which were speculated to be unreduced gametes. Premature cytokinesis, misorientation of the spindles, and aberrant cytokinesis were observed in a cytological analysis, which explained the production of unreduced pollen. Premature cytokinesis was only detected in triploid hybrids, which might be attributed to a ploidy change. The frequencies of meiotic abnormalities, such as precocious chromosomal migration, chromosome bridges, and micronuclei in the triploid hybrids were higher than those in diploid hybrids, suggesting that the unbalanced chromosomes in the triploid hybrids caused more complex meiotic chromosome behaviors. Backcrosses with the triploid hybrids resulted in low seed sets and seed germination rates, suggesting that polyploidization reduced pollen viability. Our findings provide new insight into the effect of sexual polyploidization on reproductive development in Populus and could be used to guide a Populus polyploid breeding program.

CYTOMIXIS AND MEIOTIC ABNORMAL BEHAVIOR RELATED IN SOME SELECTED SPECIES OF THE GENUS Salvia L. (Lamiaceae) FROM IRAN

In this research, the cytogenetic characteristics, phases of meiosis, abnormality during meiosis, variety of pollen grains, and cytomixis phenomenon have been studied. Populations of 10 species belonging to Salvia L. have been collected from different geographical regions of Iran. Cytomixis was recorded during meiosis I in three species of Salvia (S. nemorosa, S. staminea, S. verticellata) of the Lamiaceae family. Cytomixis and other associated meiotic abnormalities such as chromatin stickiness, clumping of metaphase -1, laggards, bridges, aberrations anaphase I, II, and micronuclei in the species reported into pollen sterility and some variable sizes. It can be said all of these are dependent on each other to create some abnormalities. Cytomixis and chromosome migration occurre in diploid and polyploid meiocytes.

Effects of cell morphology and electrical properties on electric field and dielectrophoretic force generated in cell exposed to tumor-treating field

Tumor-treating field (TTF) therapy has been receiving attention as a new minimally invasive treatment for cancer. In this treatment, an alternating electric field applied to target cells inhibits cell division by a dielectrophoretic force acting on chromosomes and microtubules. Previous studies have shown that an extremely weak electric field of only a few volts per centimeter interferes with chromosome migration and spindle formation. However, the therapeutic range of TTF treatment is still limited. To increase the efficacy of the treatment, the electric field to the target cells must be optimized. Therefore, the aim of this study was to investigate the effect of the electric field frequency, cell morphology, and electrical properties on the outcome of TTF treatment. Three-dimensional finite element models of a sphere and dividing cell were developed, and the distributions of the electric field and dielectrophoretic force were calculated.

Cytogenetic analysis of interspecific hybridization in oil-tea (Camellia oleifera)

Oil-tea (Camellia oleifera) is an important woody plant species producing edible oil in southern China, which shows complicated cytogenetics and intraspecific polyploidy. In order to explore the ploidy variation in interspecific hybridization of oil-tea Camellia, the ploidy of ‘Huashuo’, ‘Youza 2’ and 18 superior hybrids of ‘Youza 2’ × ‘Huashuo’ were identified by flow cytometry and chromosome counting. C.oleifera variety ‘Huashuo’ was hexaploid (2n = 90), and Camellia yuhsienensis superior plant ‘Youza 2’ was aneuploid based on hexaploid (2n = 91). There are not only hexaploid but also aneuploid in the ‘Huashuo’ × ‘Youza 2’ hybrids. Among the offspring plants, there are 11 plants each with chromosome number of 90, 6 plants each with 91, and 1 plants each with 92. To elucidate the causes of ploidy variation in above findings, the pollen characteristics and chromosomal behavior in meiosis of ‘Huashuo’ were examined by microscopy. The chromosome pairing configuration of meiosis terminal stage of microsporocytes of ‘Huashuo’ was 43 II + 2 IV. In all stages of meiosis, numerous abnormal behaviors were found, such as precocious chromosome migration, free chromosomes, lagging chromosomes and micronucleus. The abnormal rates of metaphase I, anaphase I, metaphase II and anaphase II were 67.5%, 88.1%, 58.4% and 78.9%, respectively. In the tetrad stage, abnormal phenomena such as dyads, triads, hexads and micronucleus were observed, with the frequency of 1.4%, 1.0%, 1.0% and 4.2%, respectively. The pollen diameter of ‘Huashuo’ varied widely (16.92–79.13 μm), suggesting a wide range of ploidy level of pollen grains. From pollen diameter distribution, we concluded that ‘Huashuo’ produced a small number of unreduced pollen grains. These findings are valuable for cytogenetics research and selection strategy of ploidy breeding in C. oleifera.

Microtubule organization defects in Arabidopsis thaliana.

Microtubules (MT) are critical cytoskeletal filaments that have several functions in cell morphogenesis, cell division, vesicle transport and cytoplasmic separation in the spatiotemporal regulation of eukaryotic cells. Formation of MT requires the co-interaction of MT nucleation and α-β-tubulins, as well as MT-associated proteins (MAP). Many key MAP contributing to MT nucleation and elongation are essential for MT nucleation and regulation of MT dynamics, and are conserved in the plant kingdom. Therefore, the deletion or decrease of γ-tubulin ring complex (γTuRC) components and related MAP, such as the augmin complex, NEDD1, MZT1, EB1, MAP65, etc., in Arabidopsis thaliana results in MT organizational defects in the spindle and phragmoplast MT, as well as in chromosome defects. In addition, similar defects in MT organization and chromosome structure have been observed in plants under abiotic stress conditions, such as under high UV-B radiation. The MT can sense the signal from UV-B radiation, resulting in abnormal MT arrangement. Further studies are required to determine whether the abnormal chromosomes induced by UV-B radiation can be attributed to the involvement of abnormal MT arrays in chromosome migration after DNA damage.

A cytogenetic analysis of male meiosis in Asparagus officinalis.

Asparagus (Asparagus officinalis) has several traits that make it a useful model for cytogenetic studies, however, few studies of the meiosis process have been made in asparagus. Here, we present in detail an atlas of male meiosis in asparagus, from preleptotene to telophase II. The meiosis process in asparagus is largely similar to those of the well-characterized model plants Arabidopsis thaliana, Zea mays, and Oryza sativa. However, most asparagus prophase I meiotic chromosomes show a strongly aggregated morphology, and this phenotype persists through the pachytene stage, highlighting a property in the control of chromosome migration and distribution in asparagus. Further, we observed no obvious banding of autofluorescent dots between divided nuclei of asparagus meiocytes, as one would expect in Arabidopsis. This description of wild-type asparagus meiosis will serve as a reference for the analyses of meiotic mutants, as well as for comparative studies among difference species. Abbreviations: DAPI: 4',6-diamidino-2-phenylindole; FISH: fluorescence in situ hybridization; PBS: phosphate-buffered saline; PMC: pollen mother cell; SEM: Scanning Electron Microscope.

Sld5 Ensures Centrosomal Resistance to Congression Forces by Preserving Centriolar Satellites.

The migration of chromosomes during mitosis is mediated primarily by kinesins that bind to the chromosomes and move along the microtubules, exerting pulling and pushing forces on the centrosomes. We report that a DNA replication protein, Sld5, localizes to the centrosomes, resisting the microtubular pulling forces experienced during chromosome congression. In the absence of Sld5, centriolar satellites, which normally cluster around the centrosomes, are dissipated throughout the cytoplasm, resulting in the loss of their known function of recruiting the centrosomal protein, pericentrin. We observed that Sld5-deficient centrosomes lacking pericentrin were unable to endure the CENP-E- and Kid-mediated microtubular forces that converge on the centrosomes during chromosome congression, resulting in monocentriolar and acentriolar spindle poles. The minus-end-directed kinesin-14 motor protein, HSET, sustains the traction forces that mediate centrosomal fragmentation in Sld5-depleted cells. Thus, we report that a DNA replication protein has an as yet unknown function of ensuring spindle pole resistance to traction forces exerted during chromosome congression.

Biometric Analysis of Melanoma Cells Due to Various Metastasis Origin

Objective: biometric analysis of melanoma cells derived from different types of primary or secondary tumors could be necessary for better understanding tumor heterogeneity as that phenomenon would affect significantly the anti-cancer therapy efficacy. Materials and Methods. A comparative analysis of melanoma cells that reflect different stages of tumor progression was accomplished with following parameters tested: intensity of apoptosis, proliferation/metabolic activity, the ratio of the cell cycle phases distribution, chromosomal constitution analysis, invasion, and migration capacity. Results. It was found that melanoma cells derived from visceral metastases characterized by a high proliferative/metabolic potential, migratory ability, and mitotic potential. Melanoma cells which represent earlier stages of carcinogenesis have higher invasive activity and percentage of polyploidy cells, indicating high mutational potential. Both cell lines have no differences in the expression of apoptosis. Conclusion. Melanoma cells derived from metastasis demonstrate various abilities for growth, migration, and invasion depending on metastasis origin. In that context, isolation of pathological cells and tissues, both native and fixed, followed by their individual testing for each patient will have a high demand for both fundamental and clinical medicine for more adequate therapy choice.

Abnormal meiosis in an intersectional allotriploid of Populus L. and segregation of ploidy levels in 2x × 3x progeny.

Triploid plants are usually highly aborted owing to unbalanced meiotic chromosome segregation, but limited viable gametes can participate in the transition to different ploidy levels. In this study, numerous meiotic abnormalities were found with high frequency in an intersectional allotriploid poplar (Populus alba × P. berolinensis ‘Yinzhong’), including univalents, precocious chromosome migration, lagging chromosomes, chromosome bridges, micronuclei, and precocious cytokinesis, indicating high genetic imbalance in this allotriploid. Some micronuclei trigger mini-spindle formation in metaphase II and participate in cytokinesis to form polyads with microcytes. Unbalanced chromosome segregation and chromosome elimination resulted in the formation of microspores with aneuploid chromosome sets. Fusion of sister nuclei occurs in microsporocytes with precocious cytokinesis, which could form second meiotic division restitution (SDR)-type gametes. However, SDR-type gametes likely contain incomplete chromosome sets due to unbalanced segregation of homologous chromosomes during the first meiotic division in triploids. Misorientation of spindles during the second meiotic division, such as fused and tripolar spindles with low frequency, could result in the formation of first meiotic division restitution (FDR)-type unreduced gametes, which most likely contain three complete chromosome sets. Although ‘Yinzhong’ yields 88.7% stainable pollen grains with wide diameter variation from 23.9 to 61.3 μm, the pollen viability is poor (2.78% ± 0.38). A cross of ‘Yinzhong’ pollen with a diploid female clone produced progeny with extensive segregation of ploidy levels, including 29 diploids, 18 triploids, 4 tetraploids, and 48 aneuploids, suggesting the formation of viable aneuploidy and unreduced pollen in ‘Yinzhong’. Individuals with different chromosome compositions are potential to analyze chromosomal function and to integrate the chromosomal dosage variation into breeding programs of Populus.

Efficiency of the induction of cytomixis in the microsporogenesis of dicotyledonous (N. tabacum L.) and monocotyledonous (H. distichum L.) plants by thermal stress

The efficiencies of the induction of cytomixis in microsporogenesis by thermal stress are compared in tobacco (N. tabacum L.) and barley (H. distichum L.) It has been shown that different thermal treatment schedules (budding tobacco plants at 50°C and air-dried barley grains at 48°C) produce similar results in the species: the frequency of cytomixis increases, and its maximum shifts to later stages of meiosis. However, the species show differences in response. The cytomixis frequency increase in tobacco is more pronounced, and its maximum shifts from the zygotene–pachytene stages of meiotic prophase I to prometaphase–metaphase I. Later in the meiosis, aberrations in chromosome structure and meiotic apparatus formation typical of cytomixis are noted, as well as cytomixis activation in tapetum cells. Thermal stress disturbs the integration of callose- bearing vesicles into the callose wall. Cold treatment at 7°C does not affect cytomixis frequency in tobacco microsporogenesis. Incubation of barley seeds at 48°C activates cytomixis in comparison to the control, shifts its maximum from the premeiotic interphase to zygotene, and changes the habit of cytomictic interactions from pairwise contacts to the formation of multicellular clusters. Thermal treatment induces cytomictic interactions within the tapetum and between microsporocytes and the tapetum. However, later meiotic phases show no adverse consequences of active cytomixis in barley. It is conjectured that heat stress affects callose metabolism and integration into the forming callose wall, thereby causing incomplete closure of cytomictic channels and favoring intercellular chromosome migration at advanced meiotic stages.

Evidence of Allopolyploidy in Urochloa humidicola Based on Cytological Analysis and Genetic Linkage Mapping.

The African species Urochloa humidicola (Rendle) Morrone & Zuloaga (syn. Brachiaria humidicola (Rendle) Schweick.) is an important perennial forage grass found throughout the tropics. This species is polyploid, ranging from tetra to nonaploid, and apomictic, which makes genetic studies challenging; therefore, the number of currently available genetic resources is limited. The genomic architecture and evolution of U. humidicola and the molecular markers linked to apomixis were investigated in a full-sib F1 population obtained by crossing the sexual accession H031 and the apomictic cultivar U. humidicola cv. BRS Tupi, both of which are hexaploid. A simple sequence repeat (SSR)-based linkage map was constructed for the species from 102 polymorphic and specific SSR markers based on simplex and double-simplex markers. The map consisted of 49 linkage groups (LGs) and had a total length of 1702.82 cM, with 89 microsatellite loci and an average map density of 10.6 cM. Eight homology groups (HGs) were formed, comprising 22 LGs, and the other LGs remained ungrouped. The locus that controls apospory (apo-locus) was mapped in LG02 and was located 19.4 cM from the locus Bh027.c.D2. In the cytological analyses of some hybrids, bi- to hexavalents at diakinesis were observed, as well as two nucleoli in some meiocytes, smaller chromosomes with preferential allocation within the first metaphase plate and asynchronous chromosome migration to the poles during anaphase. The linkage map and the meiocyte analyses confirm previous reports of hybridization and suggest an allopolyploid origin of the hexaploid U. humidicola. This is the first linkage map of an Urochloa species, and it will be useful for future quantitative trait locus (QTL) analysis after saturation of the map and for genome assembly and evolutionary studies in Urochloa spp. Moreover, the results of the apomixis mapping are consistent with previous reports and confirm the need for additional studies to search for a co-segregating marker.

Unreduced gamete formation in wheat×Aegilops spp. hybrids is genotype specific and prevented by shared homologous subgenomes.

The presence of homologous subgenomes inhibited unreduced gamete formation in wheat×Aegilops interspecific hybrids. Unreduced gamete rates were under the control of the wheat nuclear genome. Production of unreduced gametes is common among interspecific hybrids, and may be affected by parental genotypes and genomic similarity. In the present study, five cultivars of Triticum aestivum and two tetraploid Aegilops species (i.e. Ae. triuncialis and Ae. cylindrica) were reciprocally crossed to produce 20 interspecific hybrid combinations. These hybrids comprised two different types: T. aestivum×Aegilops triuncialis; 2n=ABDU(t)C(t) (which lack a common subgenome) and T. aestivum×Ae. cylindrica; 2n=ABDD(c)C(c) (which share a common subgenome). The frequency of unreduced gametes in F1 hybrids was estimated in sporads from the frequency of dyads, and the frequency of viable pollen, germinated pollen and seed set were recorded. Different meiotic abnormalities recorded in the hybrids included precocious chromosome migration to the poles at metaphase I and II, laggards in anaphase I and II, micronuclei and chromosome stickiness, failure in cell wall formation, premature cytokinesis and microspore fusion. The mean frequency of restitution meiosis was 10.1%, and the mean frequency of unreduced viable pollen was 4.84% in T. aestivum×Ae. triuncialis hybrids. By contrast, in T. aestivum×Ae. cylindrica hybrids no meiotic restitution was observed, and a low rate of viable gametes (0.3%) was recorded. This study present evidence that high levels of homologous pairing between the D and D(c) subgenomes may interfere with meiotic restitution and the formation of unreduced gametes. Variation in unreduced gamete production was also observed between T. aestivum×Ae. triuncialis hybrid plants, suggesting genetic control of this trait.

Pollen variation as a response to hybridisation in Populus L. section Aigeiros Duby

Interspecific hybrids often produce extensive gametic variation due to poor chromosome pairing and unbalanced chromosome segregation. To elucidate the influence of interspecific hybridisation on pollen variation in Populus L., we compared pollen size among three P. deltoides Marsh. clones, two P. nigra L. clones, and three P. deltoides × P. nigra hybrids and investigated the cytological mechanism of pollen variation by observing meiotic chromosome behaviour and microtubules. The frequency of shrunken and unstainable pollen grains was higher in the hybrids (15.54–57.28 %) than in the non-hybrid clones (0.98–4.82 %). The distribution of stained pollen size ranged more broadly in the hybrids than in the non-hybrids, suggesting that hybridisation increases pollen size variation. Precocious chromosome migration and lagging chromosomes were common in the hybrids, indicating poor chromosome pairing. Some micronuclei formed minispindles in metaphase II and emanated secondary nuclear-based radial microtubule systems in telophase II, undergoing cytokinesis to develop into microcytes in the meiotic products. Eliminated micronuclei might result in the formation of aneuploid pollen. The frequency of sporads with microcytes was higher in the hybrids (3.19–11.08 %) than in the non-hybrids (0–0.94 %). Disoriented spindles, including fused and tripolar spindles, led to the formation of dyads and triads, contributing to unreduced pollen production. These results provide new insights into the gametic variation of Populus interspecific hybrids and reveal several 2n pollen producers, which will be valuable in polyploid breeding of the section Aigeiros Duby.

Abnormal meiotic chromosome behavior and gametic variation induced by intersectional hybridization in Populus L.

Abnormal meiotic chromosome behavior and pollen variation in two intersectional hybrids between Populus simonii Carr. (section Tacamahaca Spach) and Populus euphratica Oliv. (section Turanga Bge.) were investigated by the squashed technique and indirect immunofluorescence. Both hybrids produced abnormal flower buds characterized by a primary bud with an accessary bud at frequencies of 39.0 and 17.8 %, respectively. Chromosome pairing analysis at late diakinesis showed average configurations 20.31 I + 7.04 II + 1.42 III + 0.04 IV in hybrid “Xhu-DK” and 19.18 I + 7.16 II + 1.45 III + 0.04 IV in hybrid “Xhu-TL”, indicating high divergence between their parent species. Meiotic abnormalities, including precocious chromosome migration, lagging chromosomes, chromosome bridges, and micronuclei, were observed at high frequency, resulting in imbalanced chromosome segregation and chromosome elimination and caused high gamete sterility. Some micronuclei triggered formation of minispindles in Metaphase II, which were responsible for the formation of microcytes. Fused and tripolar spindles in the second meiotic division developed into dyads and triads, respectively, leading to viable first meiotic division restitution (FDR) type unreduced pollen formation. However, Xhu-TL was completely sterile because the high frequency of precocious cytokinesis during the second division prevented unreduced pollen formation though spindle fusion. Xhu-DK produced 29.6 % viable pollen grains. The diameter of viable pollen ranged from 19.6 to 64.9 μm, suggesting that Xhu-DK might be capable of producing unreduced pollen or pollen with a higher ploidy level. The strategy of using the distant hybrids for chromosome introgression and polyploidy breeding in Populus L. was considered.

An overview on cytogenetics of the genusAstragalussubgenusHypoglottis(Fabaceae)

This study reports the chromosome number and meiotic behavior of 24 populations belonging to 16 species of Astragalus sect. Malacothrix from Iran. Thirteen populations showed the diploid chromosome number 2n = 2x = 16; consistent with the proposed base number of x = 8 from ICPN. However, tri-, tetra- and hexaploids were also observed in the rest of the taxa. Although the species displayed regular bivalent pairing and chromosome segregation at meiosis, non-oriented bivalents, laggard chromosomes, precocious migration of chromosomes to the poles, micronuclei, multipolar meiocytes, desynapsis, chromosome stickiness, bridges, asynchronism and cytomixis were also determined as meiotic abnormalities. Evolution in chromosome numbers in taxa belonging to A. sect. Malacothrix along with six other sections which have been classified under A. subgen. Hypoglottis is also discussed.

Identification of potential driver genes involved in chromosomal instability and tumor cell migration in hepatocarcinogenesis

Identification of potential driver genes involved in chromosomal instability and tumor cell migration in hepatocarcinogenesis