Second Division Of Meiosis Research Articles

CYTOGENETIC EFFECTS OF SURFACTANTS

Introduction. The widespread use of surfactants in economic activity and life has led to global pollution. The negative impact of surfactants on various characteristics of living organisms has been revealed, which makes a research on the safety of surfactants extremely relevant. Aim. The aim of this work was to study the genotoxic potential of anionic and cationic surfactants. Methods. The influence of anionic (sodium stearate and alkylbenzenesulpho-acid) and cationic (Praepagen TQ) surfactants on the value of the mitotic index, as well as on the regularity of mitosis and meiosis of Triticum aestivum L. cv. Odesa fantasy by standard cytogenetic methods. Main results. Under the action of surfactants in the root meristem of sprouts, the mitotic index significantly decreased and the number of cells containing chromosomal aberrations increased. Among the abnormalities at the ana-telophase stage, cells with lagging chromosomes, fragments, the formation of chromosomal bridges, and complex disorders were observed. These changes were directly proportional to the concentration of the drugs. The action of the cationic drug was less harmful than the action of both anionic drugs. Treatment of plants with surfactants led to a highly reliable increase in the proportion of abnormal MCPs in both the first and second division of meiosis, directly proportional to the concentration of surfactants applied. No differences were found between the first and second meiotic divisions in terms of the frequency of formation of defective MCPs. Both anionic surfactants had a stronger effect than the cationic one; with the use of alkylbenzenesulfonic acid, the degree of violations in microsporocytes was the greatest. Conclusions. A significant decrease in the mitotic index and an increase in the proportion of cells containing chromosomal aberrations in the root meristem of sprouts, as well as a significant increase in the proportion of abnormal MCPs in both the first and second division of meiosis, were found to be directly proportional to the concentration of surfactant. According to all the parameters studied, the action of the cationic drug “Praepagen TQ” was milder than the action of both anionic surfactants.

Микроспорогенез и образование пыльцы у лиственницы Сукачева (Larix Sukaczewii Djil.) на постоянном лесосеменном участке Семилукского лесопитомника

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

Diploid Male Gametes Circumvent Hybrid Sterility Between Asian and African Rice Species.

In F1 hybrids of Oryza sativa (Asian rice) and Oryza glaberrima (African rice), heterozygosity leads to a complete gamete abortion because of allelic conflict at each of the 13 hybrid sterility (HS) loci. We systematically produced 19 plants from the F1 hybrids of both the rice species by the anther culture (AC) method. Five of the 19 interspecific hybrid plants were partially fertile and able to produce seeds. Unlike ordinal doubled haploid plants resulting from AC, these regenerated plants showed various ploidy levels (diploid to pentaploid) and different zygosities (completely homozygous, completely heterozygous, and a combination). These properties were attributable to meiotic anomalies in the interspecific hybrid F1 plants. Examination of the genetic structures of the regenerated plants suggested meiotic non-reduction took place in the interspecific hybrid F1 plants. The centromeric regions in the regenerated plants revealed that the abnormal first and/or second divisions of meiosis, namely the first division restitution (FDR) and/or second division restitution (SDR), had occurred in the interspecific hybrid. Immunohistochemical observations also verified these phenomena. FDR and SDR occurrences at meiosis might strongly lead to the formation of diploid microspores. The results demonstrated that meiotic anomalies functioned as a reproductive barrier occurred before the HS genes acted in gamete of the interspecific hybrid. Although such meiotic anomalies are detrimental to pollen development, the early rescue of microspores carrying the diploid gamete resulted in the fertile regenerated plants. The five partially fertile plants carrying tetraploid genomes with heterozygous alleles of the HS loci produced fertile diploid pollens, implying that the diploid gametes circumvented the allelic conflicts at the HS loci. We also proposed how diploid male gametes avoid HS with the killer–protector model.

H3Ser10 histone phosphorylation in plant cell division

Histones, the main protein components of the chromatin, are exposed to posttranslational modifications that influence on peculiarities of structural and functional organization of the chromosomes. Phosphorylation, methylation, acetylation, and ubiquitination are the most spread posttranslational modifications. Phosphorylation of histones mainly happens on N-terminal domains of serines (Ser) and threonines (Thr) and is involved in regulation of different processes in mitotic and meiotic divisions. To date, it was demonstrated that this type of modification is required for the activation of transcription, repair of DNA breaks, and recombination, as well as for the condensation and divergence of chromosomes. Among the four main histones, the presence of a larger number of modification sites is typical for the H3 histone. In plants, H3 histone phosphorylation at serine in positions 10 and 28 and at threonine in positions 3, 11, 32, and 133 are the most well studied. The data known to date on the spatiotemporal distribution of H3 phosphorylation at serine in position 10 (phH3Ser10) in the mitosis and meiosis of different plant species are collected in the review. For most species, phosphorylation of only pericentromeric regions in mitosis and the second division of meiosis and along the entire length of the chromosomes in the first meiotic division is typical. However, there are exceptions in the phH3Ser10 distribution in mosses and in the Cestrum genus, as well as in species with holocentric chromosomes. Controversial data on the phH3Ser10 distribution in mitosis and meiosis in the same species are found. The functional significance of phH3Ser10 in the cellular division in plants is associated with the activity of the centromere, the cohesion of the centromeres and sister chromatids, and chromosome segregation. The involvement of candidates of kinases and phosphatases known to date in the dynamics of H3Ser10 phosphorylation is discussed. The review provides an overview of the role of phH3Ser10 modifications in the chromosome division and segregation in mitosis and meiosis.

Interpolar microtubules are dispensable in fission yeast meiosis II

The mitotic spindle consists of two types of microtubules. Dynamic kinetochore microtubules capture kinetochores, whereas stable interpolar microtubules serve as the structural backbone that connects the two spindle poles. Both have been believed to be indispensable for cell division in eukaryotes. Here we demonstrate that interpolar microtubules are dispensable for the second division of meiosis in fission yeast. Even when interpolar microtubules are disrupted by a microtubule-depolymerizing drug, spindle poles separate and chromosomes segregate poleward in second division of meiosis in most zygotes, producing viable spores. The forespore membrane, which encapsulates the nucleus in second division of meiosis and is guided by septins and the leading-edge proteins, is responsible for carrying out meiotic events in the absence of interpolar microtubules. Furthermore, during physiological second division of meiosis without microtubule perturbation, the forespore membrane assembly contributes structurally to spindle pole separation and nuclear division, generating sufficient force for spindle pole separation and subsequent events independently of interpolar microtubules.

Development of juman male meiosis in vitro.

Testes material from 16 men was used to study the development of human meiosis in vitro. The present report deals with the results from the analysis of the cells from the organ cultures of five of these men. H3-thymidine was added to the culture medium for 75 to 90 minutes. The isotope was removed and the cells were thoroughly washed in 3 changes of fresh medium without tritium. Subsequently they were incubated at 36°C for 14 days. Feulgen squashes and sections were prepared and labelled cells were photographed. After this procedure the silver grains were removed from the autoradiographs in order to identify the meiotic stages. The most advanced stages found labelled, after the cells had been in culture for 14 days, were the following: prometaphase I, metaphase I, prophase II and telophase II. Under the culture conditions used human spermatocytes are able to develop in vitro from DNA synthesis to the end of the second division of meiosis.

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3-5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3–5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

A probability model for the meiosis I non-disjunction fraction in numerical chromosomal anomalies.

Numerical chromosome abnormalities (aneuploidies) are among the most common known causes of mental retardation and the leading cause of pregnancy loss in humans. They primarily arise by the process of meiotic non-disjunction. We still know very little about the contribution of genetic and environmental causes for non-disjunction in humans. In order to increase our understanding of the epidemiology of human trisomies, it is necessary to establish the proportion of cases occurring in the first or second division of meiosis. Trisomic patients will display, in study of microsatellite typed by the polymerase chain reaction (PCR), three fragment peaks of equal intensity, two fragments at an average 2:1 dosage or one individual fragment. In this work we describe a statistical approach for estimation of the fraction of meiosis I non-disjunctions (F) in the absence of the parental information. First we determine a probability model for the number of peaks in a polymorphic microsatellite locus, which is a function of F. Based on this model, we obtain a maximum likelihood estimator for F, using the observed proportion of one, two and three allele patterns in trisomic individuals. Relying on the properties of maximum likelihood theory, we also calculate the asymptotic variance and confidence intervals for F. Owing to the fact that the samples of trisomic patients are limited in number, the use of asymptotic theory may be compromised. Thus, we employ the bootstrap technique to build confidence intervals for F and compare the results with those obtained from the normal theory. This estimator that dispenses the need to study parents opens the possibility of using archival material for comparative epidemiological studies of Down's syndrome and other aneuploidies. In this paper we propose a probability model to estimate the fraction of meiosis I non-disjunction, F, by only using the proportion of allele patterns of trisomy individuals, while traditional methods require typing pericentromeric markers from those affected and their parents.

Megasporogenesis in Arabidopsis thaliana L.: an ultrastructural study

In this study, megasporogenesis of the plant model Arabidopsis thaliana was investigated by electron microscopy for the first time. The data described here could constitute a reference for future investigations of Arabidopsis mutants. During the beginning of meiosis the megaspore mother cell shows a polarity created by unequal distribution of organelles in the cytoplasm. Plastids accumulate in the chalazal region and long parallel saccules of endoplasmic reticulum, small vacuoles and some dictyosomes are found in the micropylar region. Plasmodesmata are abundant in the chalazal cell wall. The nucleus is almost centrally localized and contains a prominent excentric nucleolus and numerous typical synaptonemal complexes. After the second division of meiosis the four megaspores are separated by thin cell walls crossed by numerous plasmodesmata and do not show significant cellular organization. The young functional megaspore is characterized by a large nucleus and a large granular nucleolus. The cytoplasm is very electron dense due to the abundance of free ribosomes and contains the following randomly distributed organelles: mitochondria, a few short saccules of endoplasmic reticulum, dictyosomes and undifferentiated plastids. However, there is no apparent polarity, except for the distribution of some small vacuoles which are more abundant in the micropylar region of the cell. The degenerating megaspores are extremely electron dense and do not show any substructure.

Meiotic chromosomes: it takes two to tango.

Meiosis is a special type of cell division that produces haploid gametes from diploid parental cells. Chromosome number is reduced during meiosis because a single round of DNA replication is followed by two rounds of chromosome segregation (Fig. 1). Fusion of two gametes during sexual reproduction restores the diploid chromosome complement. The second division of meiosis (the equational division) resembles mitosis: Sister chromatids separate and segregate. The first division, however, is unique. Reductional chromosome segregation at meiosis I differs from mitosis and meiosis II in a number of respects. First, sister chromatids remain associated with each other. Second, the two copies of the same chromosome (called homologous chromosomes or homologs) behave in a coordinate fashion, such that one chromosome moves to one pole of the spindle apparatus and its homolog moves to the opposite pole. This coordination in chromosome behavior depends on complex processes and elaborate structures that bring homologs together during meiotic prophase and hold them together until the transition between metaphase I and anaphase I. In most organisms, the relevant processes include alignment of homologs, assembly of the synaptonemal complex (SC, described below), genetic recombination, and the formation of chiasmata (stable connections between homologs formed at the sites of crossovers). These events occur during a very lengthy prophase that is divided into a series of substages based on changes in chromosome morphology (Table 1). This article reviews our current knowledge of the processes and structures that promote and maintain interactions between homologs and thereby ensure proper reductional chromosome segregation. Emphasis is placed on observations made in recent years, particularly those that have enhanced our understanding of the molecular mechanisms underlying meiotic chromosome behavior.

Homotypic: a wrong definition for the second division of meiosis (hemiosis)

SUMMARYThe classic cytological term «homöotypisch» («Theilungsform») by FLEMMING (1887), is rightly translated into the English «homoeotypic», which is preferable to the alternative and acceptable form «homeotypic». Both prefixes «homoeo-» and «homeo-» derive from the Greek öμoιoς = «similar», «like». By contrast, the common tendency to accept the expression «homotypic division», should be avoided as a misnomer, because the prefix «homo» derives from the Greek ὁμóς= «the same».

The F-actin distribution during microsporogenesis in Magnolia soulangeana Soul. (Magnoliaceae)

F-actin distribution during male meiosis in Magnolia soulangeana was studied by means of fluorescence microscopy following staining with rhodaminephalloidin. Actin filaments were observed to persist during all of the developmental stages of meiosis. Four main types of configurations were recognized: (1) peripheral filaments underlying the plasma membrane (cortical network); (2) filaments dispersed throughout the inner cytoplasm (central cytoplasmic network); (3) filaments associated with the meiotic spindles; (4) filaments associated with the phragmoplasts. The cortical and central cytoplasmic filaments exhibited different behaviours. Whereas the cortical network remained present in an apparently unchanged form during all of the meiotic stages, the central cytoplasmic filaments, although they never completely disappeared, were reduced and concentrated around the nucleus at the end of prophase. At metaphase, fluorescent spindles consisting of filament bundles running from pole to pole or being interrupted at the equatorial zone could be seen. At the end of both the first and second division of meiosis, fluorescent bands of filaments (disks) appeared at the level of the cell division planes (equatorial regions) where cleavage furrows were constituted. These cleavage furrows did not form when floral buds were “cultivated” in a cytochalasin-containing medium. Our results show that during microsporogenesis in M. soulangeana the actin filaments constitute a highly complex and dynamic system that is involved in particular in cytoplasm cleavage of the meiocytes.

Introgression of Solarium acaule germ plasm from the endosperm balance number 2 gene pool into the cultivated endosperm balance number 4 potato gene pool via triplandroids

Triploid plants from interspecific crosses between selected clones of Solanum acaule and a 2n pollen producing, cultivated diploid expressed an average of 7.7% to 2n pollen, called triplandroids. Percent stainable pollen of these triploids ranged from 1.8 to 22.1%. The cytological mechanism of 2n pollen formation was parallel orientation of spindles in the second division of meiosis. Three triplandroid-producing triploids were crossed to several tetraploid potato cultivars and breeding clones. Of these 4x−3x pollinations, 49% produced berries, containing an average of 15.2 seeds. Progeny from 4x−3x crosses were 67% pentaploid, 2n = 60, and 33% aneuploids 2n = 56–59, mostly 2n = 59. Thus, functional microspores from triploids were predominantly triplandroids, 2n = 3x = 36, with low frequencies of aneuploidy. This use of a triplandroid bridge is a rapid means of introducing S. acaule germ plasm to the cultivated tetraploid gene pool.Key words: interspecific hybrids, parallel spindles, pollen restitution, triploidy, 2n pollen.

A semiselective test for the detection of first- and second-division nondisjunction in Drosophila melanogaster.

Little is known about the relative frequency of induction of nondisjunction in the first and second divisions of meiosis. The killer of prune system is a semiselective Drosophila aneuploidy assay designed to detect chromosome gain resulting from first- or second-division nondisjunction in males. The system can also detect X-Y interchange. Extensive data from nonmutagenized controls indicate that all the expected phenotypes can be recovered. Spontaneous nondisjunction in the first division is three times more frequent than in the second division. Spontaneous interchange between the X chromosome and YS is six times more frequent than between the X chromosome and YL. Exposures of larval males to X-rays, 35 degrees C heat shock, and colchicine were performed. X-ray exposure induced an increase in X-Y interchange events only. A 24-hr heat shock induced an increase in first-division nondisjunction and one type of interchange event. Colchicine failed to induce both nondisjunction and interchange, although it did decrease fertility. The Killer of prune test is of potential value because it allows for the assessment of the relative sensitivities of the two meiotic divisions to perturbations in chromosome number.

Membranes in the spindle of Iris pollen mother cells during the second division of meiosis

Spindle membrane in the second division of meiosis inIris comprises endoplasmic reticulum (ER) and small spherical vesicles (40–80 nm diameter). The vesicles are in all respects similar to those of dictyosomes and it is proposed that they originate in the Golgi system. ER on the other hand is generated from the nuclear envelope (NE). Invaginations and evaginations of the inner and outer membranes of the NE are present at interphase and they enlarge during prophase II and break to form spindle ER elements at the beginning of prometaphase II. The area enclosed by this ER continues to increase until the entire spindle is filled with irregular profiles at mid-prometaphase II. During late-prometaphase II the quantity of ER decreases and, concurrent with an increase in the number of microtubules (MTs), the cisternae align alongside MT bundles and accumulate at the poles. It is suggested that ER increases in quantity by growth of NE membranes. Furthermore, the alignment of ER along the interpolar axis and its transport polewardsprior to anaphase suggest the action of a force on each ER element.

Elevated recombination and pairing structures during meiotic arrest in yeast of the nuclear division mutant cdc5

A diploid strain of yeast, homozygous for the mutation cdc5-1, undergoes a normal meiosis at 25 degrees C. At the nonpermissive temperature of 34 degrees C, meiosis is arrested at the first meiotic division, after premeiotic DNA replication and recombination commitment have taken place. Haploidisation commitment does not occur at 34 degrees C. Electron microscopy reveals that synaptons (synaptonemal complexes) are formed and the stage of arrest is characterised by a prevalence of "modified synaptons", which consist of paired lateral elements lacking the central elements. Prolonged incubation at this stage of arrest results in unusually high recombination levels, perhaps related to the synaptonal structures observed. Temperature shift-up experiments (transfers of cell from 25 degrees C to 34 degrees C at various times during meiosis) reveal that the CDC5 function is required for both the first and the second divisions of meiosis.

The nuclear cycle of the myxomycete Echinostelium minutum: II. Cytophotometric analysis of the nuclear DNA content of the sporangial phase

Nuclei of uncleaved sporangia of Echinostelium minutum isolate D-3 1971 have a mean Feulgen-DNA content of 1.84. This value does not differ significantly from that recorded for the nuclei of the amoebal and plasmodial phases. No nuclei were found with a DNA content twice that of the nuclei in the amoebae, plasmodia, or uncleaved sporangia. This observation appears to rule out the possibility of zygotic meiosis. A single endosporic nuclear division occurs during the maturation which follows spore cleavage. The mean DNA content of the metaphases measured was 1.99. No metaphases were observed with a DNA content that would be indicative of a second division of meiosis. Also, no 4:2:1 reduction in DNA content was observed. These data confirm our previous hypothesis that this isolate of E. minutum normally lacks a sexual phase. The single nuclear division in the maturing spore is followed by one of the division products becoming euchromatic and undergoing a single round of DNA replication, while the other division product becomes very pycnotic, eventually degenerating. The mean nuclear DNA values for the euchromatic and pycnotic nuclei are 1.84 and 0.88, respectively. Mature spores normally become uninucleate and have a nuclear DNA content which is equivalent to that of the amoebal and plasmodial phases.

The Behavior of the Nucleolus During Nuclear Divisions in the Asci ofPyronema Domesticum

During the first division of meiosis in the asci of Pyronema domesticum the nucleolus is retained within the nuclear envelope and migrates to one pole. The nucleolus is expelled from the nucleus into the cytoplasm as a single unit during early metaphase of the second division of meiosis and the post-meiotic mitotic division. In all three nuclear divisions in the ascus, the nucleolus persists until anaphase, or possibly until telophase.

A system for the study of meiotic non-disjunction using Sordaria bervicolis

Abstract A system is described for the study of abnormal chromosome segregation in Sordaria brevicolis . The system utilizes two complementing alleles of the b 1 locus on linkage group II. Abnormal asci containing black disomic ascospores were detected which fall into two main categories. (a) Non disjunctional asci in which the disomic spores were present together with an equal number of abortive (nullosomic) spores and (b) asci in which an extra replication of the chromosomes had occurred resulting in pseudo-wild types being formed without accompanying spore abortion. Calculations indicate that the non-disjunction frequencies at the first and second divisions of meiosis are 4.25×10 −4 and 4.35×10 −4 respectively. It is suggested that the system is potentially a valuable one both for the study of meiotic non-disjunction and other causes of aneuploidy.