Abnormal Chromosome Distribution Research Articles

Nuclear-cytoplasmic asynchrony in oocyte maturation caused by TUBB8 variants via impairing microtubule function: a novel pathogenic mechanism

BackgroundTUBB8, a crucial gene encoding microtubule protein, plays a pivotal role in cellular processes. Deleterious TUBB8 variants have been shown to significantly hinder oocyte maturation. In this study, we conducted an in vitro investigation using TUBB8 mutant mouse oocytes to elucidate the pathogenic mechanisms of TUBB8 variants in oocyte nuclear and cytoplasmic maturation.MethodsA mutant model was successfully established in mouse oocytes via microinjection to further investigate the effects of four novel discovered TUBB8 mutations on the nuclear and cytoplasmic maturation of mouse oocytes. Immunofluorescence and confocal microscopy were performed to observe the cortical polarity and spindle and of mutant oocytes. Active mitochondrial staining was performed to analyze mitochondrial distribution patterns. Endoplasmic reticulum and Ca2+ staining were conducted to assess ER distribution and cytoplasmic calcium ion concentration in oocytes.ResultsIn mouse oocytes, TUBB8 variants (p.A313V, p.C239W, p.R251Q, and p.G96R) resulted in a reduction of the first polar body extrusion rate, disruption of spindle assembly, and abnormal chromosome distribution. Additionally, these variants induced oocyte organelle abnormalities, including anomalies in mitochondrial redistribution and endoplasmic reticulum stress compared to the wild-type.ConclusionDeleterious TUBB8 variants could disrupt microtubule function, affecting critical processes such as spindle assembly, chromosome distribution, and organelle rearrangement during oocyte meiosis. These disruptions culminate in compromised nuclear-cytoplasmic maturation, consequently giving rise to oocyte maturation defects.

Aquatic beetles Cercyon unipunctatus as bioindicators of pollution in Lake Edku and Mariut, Egypt.

The lakes of the North Delta give a rich and imperative territory for marine fish and its regeneration, and have dependably been major areas of fish creation in Egypt, 75% of the production was collected from them. As of late, many difficulties are confronting these lakes and prompt the exhaustion of fish production from them. The aim of the present study is to evaluate different inorganic pollutants in Coleopterons aquatic insect (Cercyon unipunctatus) taken from both Lake Edku and Mariut and also, to estimate their effect on oxidative stress markers and chromosomal aberrations. The average concentrations of heavy metals differ in the two locations. The concentration of (Pb, Cd, Fe, Co, Cu, Zn, and Mn) was significantly higher in water samples of Lake Mariut than those of Lake Edku. Also, the present work, showed the physical and chemical characters of the two lakes water. In the current study, the obtained results showed that there was a significant increase in (Pb, Cd, Fe, Co, Cu, Zn, and Mn) concentrations in C. unipunctatus tissues which were collected from Lake Mariut. The biochemical parameters of oxidative stress have been affected by the pollution in Lake Mariut water. Significant increases in the activity level of aspartate aminotransferase, alanine aminotransferase, and malondialdehyde concentration were recorded, while there were significant decreases in (total protein content, GSH content, and GPx activity). The result of chromosomal aberration test showed that there were different types of aberrations as binucleate cell, lagging chromosome, and abnormal distribution of chromosomes. The obtained data showed that C. unipunctatus highly affected by environmental stressors in water. So we suggest that these beetles could be a suitable monitor for ecotoxicological studies.

The distribution of profilin in root-tip cells of wheat seedlings exposed to enhanced UV-B radiation

ABSTRACTActin filaments play a significant role in regulating the cell cycle. The dynamic rearrangement of actin filaments are regulated by actin-binding proteins profilin (PFN). However, the distribution of PFN in root-tip cells and the role of PFN in the UV response have been unknown. Here, we observed the distribution of PFN during every stage of wheat cell mitosis in the control and UV-B treatment group, and found that PFN showed a punctuate pattern of localization around the periphery of nuclear envelopes in interphase and gathered toward the cell bipolar in prophase in the control treatment group. During metaphase, PFN presented a cage shape that is formed around the chromosomes, then appeared in the equator during anaphase, and re-distributed around the periphery of nuclear envelopes during cytokinesis. But PFN localization had changed under enhanced UV-B radiation (10.08 kJm–2 h–1), PFN displayed an annular distribution in interphase and, during metaphase, relatively large number of PFN distributed in one of the four corners or gathered in the four corners in the cell. However, two corners of PFN moved to the other two corners along the direction perpendicular to the cell-elongating axis during telophase. And these aberrant distributions of PFN were often associated with abnormal chromosome distribution.

Pollen viability and meiotic behaviour in intraspecific hybrids of Hydrangea aspera subsp. aspera Kawakami group x subsp. sargentiana

AbstractPollen viability and male meiosis in intraspecific hybrids of Hydrangea aspera subsp. aspera Kawakami group (2n = 2x = 36) and subsp. sargentiana (2n = 2x = 34) were investigated. Although it had been assumed that they were sterile, pollen viability was observed; it varied from 2.5% to 12.1%. The production of gametes with different chromosome numbers was implied by the analysis of the dispersion of the diameter distribution of pollen grains. Analysis of male meiosis made it possible to identify the origins with two major categories of meiotic aberrations: abnormal chromosome distribution (early chromosome migration at metaphase, lagging chromosomes at anaphase, micronuclei at telophase), leading to the formation of unbalanced tetrads and/or ones with supernumerary microspores; and abnormal spindle orientation in metaphase II (tripolar, fused and parallel spindles), leading to the formation of dyads or triads. The mode of 2n pollen formation is of the First Division Restitution type. The high level of parental heterozygosity that is normally associated with them should facilitate the transfer of a polygenic trait in breeding programme.

Abnormal Distribution of Chromosomes in the First Division of Nuclear Transferred Mouse Embryos

The majority of somatic cell nuclear transferred (SCNT) embryos die before or after implantation. Many studies have focused on morphological remodeling of the donor nucleus and its associated cytoskeletal structures in the early events of nuclear transfer. However, little is known about the 2-cell stage of SCNT embryos after the first division. In this study, we compared the morphological status of chromosomal division during the 1-cell stage to the 2-cell stage in SCNT embryos with that in intracytoplasmic sperm injection (ICSI) embryos. The microtubules and cytoplasmic asters, which are related to chromatin segregation, disappeared at the pronuclear stage, although formation of the first mitotic spindle was normal in both the SCNT and ICSI embryos. However, nuclear fragmentation was observed in 30% of the 2-cell SCNT embryos and 12% of the 2-cell ICSI embryos. Nuclear fragmentation was present in both blastomeres of these embryos. No apoptotic DNA fragmentation was observed in TdT-mediated dUTP-biotin Nick End Labeling (TUNEL) assays for either the SCNT or ICSI embryos. In both the SCNT and ICSI embryos, the distribution of chromosomes in the first mitotic spindle was disturbed during the process of division from the 1-cell stage to the 2-cell stage. These results suggest that loss of SCNT embryos just before or after implantation may be due to an abnormal chromosome distribution at the 2-cell stage.

A new theory of the origin of cancer: quantum coherent entanglement, centrioles, mitosis, and differentiation

Malignant cells are characterized by abnormal segregation of chromosomes during mitosis (“aneuploidy”), generally considered a result of malignancy originating in genetic mutations. However, recent evidence supports a century-old concept that maldistribution of chromosomes (and resultant genomic instability) due to abnormalities in mitosis itself is the primary cause of malignancy rather than a mere byproduct. In normal mitosis chromosomes replicate into sister chromatids which are then precisely separated and transported into mirror-like sets by structural protein assemblies called mitotic spindles and centrioles, both composed of microtubules. The elegant yet poorly understood ballet-like movements and geometric organization occurring in mitosis have suggested guidance by some type of organizing field, however neither electromagnetic nor chemical gradient fields have been demonstrated or shown to be sufficient. It is proposed here that normal mirror-like mitosis is organized by quantum coherence and quantum entanglement among microtubule-based centrioles and mitotic spindles which ensure precise, complementary duplication of daughter cell genomes and recognition of daughter cell boundaries. Evidence and theory supporting organized quantum states in cytoplasm/nucleoplasm (and quantum optical properties of centrioles in particular) at physiological temperature are presented. Impairment of quantum coherence and/or entanglement among microtubule-based mitotic spindles and centrioles can result in abnormal distribution of chromosomes, abnormal differentiation and uncontrolled growth, and account for all aspects of malignancy. New approaches to cancer therapy and stem cell production are suggested via non-thermal laser-mediated effects aimed at quantum optical states of centrioles.

XCS-1, a maternally expressed gene product involved in regulating mitosis in Xenopus.

The regulation of the cell cycle during early development is an important and complex biological process. We have cloned a cDNA, XCS-1, that may play an important role in regulating mitosis during early embryogenesis in Xenopus laevis. XCS-1 is a maternally expressed gene product that is the Xenopus homologue of the human cleavage signal protein (CS-1). XCS-1 transcripts were detected in oocytes with the titer decreasing just prior to the MBT. During development the XCS-1 protein was detected on the membrane and in the nucleus of blastomeres. It was also detected on the mitotic spindle in mitotic cells and on the centrosomes in interphase cells. Overexpression of myc-XCS-1 in Xenopus embryos resulted in abnormal mitoses with increased numbers of centrosomes, multipolar spindles, and abnormal distribution of chromosomes. Also, we observed incomplete cytokinesis resulting in multiple nuclei residing in the same cytoplasm with the daughter nuclei in different phases of the cell cycle. The phenotype depended on the presence of the N terminus of XCS-1 (aa 1-73) and a consensus NIMA kinase phosphorylation site (aa159-167). Mutations in this site affected the ability of the overexpressed XCS-1 protein to produce the phenotype. These results suggest that XCS-1 is a maternal factor playing an important role in the regulation of the cell cycle during early embryogenesis and that its function depends on its state of phosphorylation.

Chromosome spatial order in human cells: evidence for early origin and faithful propagation.

We have investigated the origin and nature of chromosome spatial order in human cells by analyzing and comparing chromosome distribution patterns of normal cells with cells showing specific chromosome numerical anomalies known to arise early in development. Results show that all chromosomes in normal diploid cells, triploid cells and in cells exhibiting nondisjunction trisomy 21 are incorporated into a single, radial array (rosette) throughout mitosis. Analysis of cells using fluorescence in situ hybridization, digital imaging and computer-assisted image analysis suggests that chromosomes within rosettes are segregated into tandemly linked "haploid sets" containing 23 chromosomes each. In cells exhibiting nondisjunction trisomy 21, the distribution of chromosome 21 homologs in rosettes was such that two of the three homologs were closely juxtaposed, a pattern consistent with our current understanding of the mechanism of chromosomal nondisjunction. Rosettes of cells derived from triploid individuals contained chromosomes segregated into three, tandemly linked haploid sets in which chromosome spatial order was preserved, but with chromosome positional order in one haploid set inverted with respect to the other two sets. The spatial separation of homologs in triploid cells was chromosome specific, providing evidence that chromosomes occupy preferred positions within the haploid sets. Since both triploidy and nondisjunction trisomy 21 are chromosome numerical anomalies that arise extremely early in development (e.g., during meiosis or during the first few mitoses), our results support the idea that normal and abnormal chromosome distribution patterns in mitotic human cells are established early in development, and are propagated faithfully by mitosis throughout development and into adult life. Furthermore, our observations suggest that segregation of chromosome homologs into two haploid sets in normal diploid cells is a remnant of fertilization and, in normal diploid cells, reflects segregation of maternal and paternal chromosomes.

Discovery of a synaptic mutant in potato haploids and its usefulness for potato breeding

A synaptic mutant was found in haploids (2n=2x=24) extracted from the Mexican potato variety 'Atzimba' (2n=4x=48). The mutant is inherited as a simple Mendelian recessive, designated sy4. Meiotic abnormalities of the mutant during microsporogenesis include: poor synapsis at pachytene; high frequency of univalents at diakinesis; elongated and curved spindles and univalents being scattered over the spindles at metaphase I and anaphase I; abnormal chromosome distribution at anaphase I; and production of sterile pollen, presumably due to unbalanced chromosome complement. The expression of sy4 in megasporogenesis was also detected. The sy4 mutant is very useful for potato breeding when combined with another meiotic mutant, parallel spindles (ps), because haploids homozygous for sy4 and ps produce fertile 2n pollen which transmit almost intact genotypes of the parents to the progenies. Thus, the meiotic mutants provide a powerful breeding method for maximizing heterozygosity and epistasis. They can also provide a very efficient method of transferring diploid germplasm, which has desired characteristics efficiently combined at the 2x level, to tetraploids. Many haploids have been identified with 2n pollen production by ps alone or by sy4 and ps, vigorous growth and good flowering, and a high level of resistance to late blight. The importance of a further search for meiotic mutants and their use for breeding is discussed.

Binucleation and abnormal chromosome distribution inEuglena gracilis cells treated with dimethyl sulfoxide

The addition of 5% of dimethyl sulfoxide (DMSO) to cultures ofEuglena gracilis in the logarithmic phase of growth caused an immediate inhibition of cell multiplication and motility without completely blocking nuclear division. Importantly, some 50% of the cells were 2–3 times larger than normal and were also binucleate after 24–48 hours of treatment. Evidently binucleation resulted from the lack of cytokinesis after mitosis was induced. Transmission electron microscopy, using serial sections, showed the occurrence of nuclei either with a normal or a reduced number of chromatin masses. Solvent withdrawal led to a rapid recovery of all the normal cell activities.

A cell line from an anaplastic transitional cell carcinoma of human urinary bladder.

A cell line, TCCSUP, derived from an undifferentiated, Grade IV transitional cell carcinoma is described. The karyotype showed an abnormal distribution of chromosomes, with no obvious modal number. Distinct marker chromosomes were observed in both early and late in vitro passages. These cells have been subcultured over 50 times during a 20-month period. TCCSUP differs in certain morphological and immunological features from other cell lines from transitional cell carcinomas.

Chromosome Behaviour of a Spontaneous Autotetraploid Guava (<i>Psidium guajava</i>, L.)

The autotetraploid form of Psidium guajava, L. reveals highly irregular meiotic division. It shows multivalents, abnormal distribution of chromosomes at anaphase, equatorial disjunction of a laggard, spindle fusion during second meiotic division, formation of stray chromosome and micronuclei. Mode of origin of this polyloid and its sterility have been discussed.

Desynapsis and chromosome breaks in a mutant of Pisum sativum

An X-ray induced mutant of Pisum sativum shows considerable meiotic irregularities caused by a reduction of chiasma frequency and the occurrence of chromosome breakage during the first meiotic prophase. In the subsequent stages univalents, fragments and bridges arise, resulting in abnormal chromosome distribution and complete sterility of the mutant. The simultaneous occurence of reduced chiasma frequency and chromosome breakage seems suitable to test the hypothesis of LEWIS AND JOHN 5 that chromosome breakage might be produced by errors in the cross-over process. The following results of our investigations are regarded as a confirmation of this assumption. 1. 1. Both chromosome breakage and reduced chiasma frequency take place in meiotic prophase during the four-strand stage. In both cases 2 of the 4 chromatids are involved in the exchange process, and in both cases the exchange is complete and reciprocal. 2. 2. The investigation of anthers being fixed at two different developmental stages of ontogenesis—immediately after entering flowering period and 4 weeks later—reveals remarkable differences as far as the amount of reduced chiasma frequency and aberration frequency is concerned. Both these factors change in the same way: the greater the number of chiasmata, the higher the number of aberrations, and vice versa. 3. 3. A comparison between fragment size at metaphase I and chiasma distribution in the bivalents shows that chromosome breakage and chiasma formation are located in the same chromosome regions. Because of the predominance of sister-chromatid reunions, the possibility is discussed that ineffective chromosome pairing might be responsible for both the reduced chiasma frequency and the occurence of fragments and bridges.

Cytogenetics of x-ray induced aneuploids in Arachis hypogaea L.

Four mutant groundnuts, Arachis hypogaea L., carrying aneuploid chromosomes were isolated. Meiotic anomalies such as univalent formation, lagging and abnormal distribution of chromosomes were common to all. Cytomixis was observed in two of the mutants and these were sterile. The meiotic anomalies, however, did not affect the pollen fertility appreciably.The mutants were conspicuous by their large inflorescences. Their reduced vigor suggests that the addition of chromosome (s) exerts a deleterious effect.The extra chromosome in a fertile trisomic mutant carried the mutant characteristic and hence was easily identified in the segregating progenies.

The effect of radiostrontium on mouse testes.

Male mice were injected intraperitoneally or intravenously with Sr/sup 90/ at 75 days of age. A quantitative effect on the testicular epithelium was obvious from 5 to between 30 and 35 days after injection, The type-B spermatogonium did not seem to have ceased but to some extent only retarded while the type-A spermatogonium was severely affected. Qualitative changes in the first meiotic division were noticed during the damage period, and signs of abnormal distribution of chromosomes in the anaphase appeared during the recovery period. (auth)