Nuclear Differentiation in Exconjugants of Paramecium caudatum: Role of Nuclear Division in Differetiation

It has been known that, immediately after the third division of fertilization nucleus (synkaryon), nuclei localized near the posterior region of exconjugant are to be macronuclear anlagen and those near the anterior region are to be presumptive micronuclei in Paramecium caudatum. One of such posterior nuclei was transplanted into amicronucleate cell at vegetative phase in this work. The implanted nuclei were able to divide at every fission. Their DNA content was nearly equal to or less than ordinary micronuclei during vegetative phase. When conjugation was induced between clones obtained and amicronucleates, macronuclear anlagen developed from the division products of implanted nuclei and thereafter derivative caryonides were true to the marker gene of implanted nuclei. The results indicate that there was no intrinsic difference between nuclei localized anteriorly and those situated posteriorly in exconjugant. Differentiation of nuclei into macronucleus may be irreversible at the stage of anteroposterior localization of the nuclei. The role of nuclear division in differentiation may be only to transport the daughter nuclei into the cytoplasm/cortex differentiated anteroposteriorly.     

Phragmoplasts in the Absence of Nuclear Division

All land plants (embryophytes) use a phragmoplast for cytokinesis. Phragmoplasts are distinctive cytoskeletal structures that are instrumental in the deposition of new walls in both vegetative and reproductive phases of the life cycle. In meristems, the phragmoplast is initiated among remaining non-kinetochore spindle fibers between sister nuclei and expands to join parental walls at the site previously marked by the preprophase band of microtubules (PPB). The microtubule cycle and cell cycle are closely coordinated: the hoop-like cortical microtubules of interphase are replaced by the PPB just prior to prophase, the PPB disappears as the spindle forms, and the phragmoplast mediates cell plate deposition after nuclear division. In the reproductive phase, however, cortical microtubules and PPBs are absent and cytokinesis may be uncoupled from the cell cycle resulting in multinucleate cells (syncytia). Minisyncytia of 4 nuclei occur in microsporocytes and several (typically 8) nuclei occur in the developing megagametophyte. Macrosyncytia with thousands of nuclei may occur in the nuclear type endosperm. Cellularization of syncytia involves formation of adventitious phragmoplasts at boundaries of nuclear-cytoplasmic domains (NCDs) defined by radial microtubule systems (RMSs) emanating from non-sister nuclei. Once initiated in the region of microtubule overlap at interfaces of opposing RMSs, the adventitious phragmoplasts appear structurally identical to interzonal phragmoplasts. Phragmoplasts are constructed of multiple opposing arrays similar to what have been termed microtubule converging centers. The individual phragmoplast units are distinctive fusiform bundles of anti-parallel microtubules bisected by a dark mid-zone where vesicles accumulate and fuse into a cell plate.     

Nuclear and Cell Division in Filamentous Bacteria

GROWTH in unicellular bacteria usually takes place as a sequence of events culminating in cell division^1–6. In some cases, however, bacteria grows in chains (referred to here as filaments). Two reasons have been put forward for this: either the individual segments of a filament are complete cells in which the timing of separation from adjacent segments is an imprecise event, not coordinated with overall growth, or the production of filaments may be a controlled process which is a prerequisite to cell division. There is some support for the first possibility⁷, but more recently it has been observed that the chain length of filamentous bacteria depends on the growth medium^8,9. Here we report further evidence that in the bacterium Bacillus subtilis the production of filaments of up to sixteen nuclei is part of a programme of events necessary for the maintenance of particular rates of cell division and that the structure and physiology of this bacterium can be explained along the same lines as those of the models describing growth in the unicellular intestinal bacteria Escherichia coli and Salmonella typhimurium.     

Nuclear Division in the Ameboflagellate Adelphamoeba galeacystis

Nuclear division in synchronized cultures of the ameboflagellate Adelphamoeba galeacystis has been described. Division in this organism is typically promitotic. It occurs within an intact nuclear membrane and is characterized by the persistence of the nucleolus and its transformation into 2 polar masses. The nucleolus is stained with pyronin-Y by the methyl green pyronin-Y technic, and with Heidenhain's hematoxylin, but is unstained by the Feulgen reaction. The reaction with these stains is removed after digestion of the nucleolus by ribonuclease. During mitosis the nucleolus undergoes an orderly series of vacuolizations before forming the polar masses. The chromatin is Feulgen positive, stains with methyl green by the methyl green pyronin-Y technic and undergoes a series of characteristic changes during the division process. Synchronization of amebae grown on coverglasses was accomplished by transfer of cells from 30 to 38.5 C for a period of 100 min. A temporal sequence of nucleolar and chromatin participation in the nuclear division of this organism is suggested.     

Daughters at Risk of Female Genital Mutilation: Examining the Determinants of Mothers’ Intentions to Allow Their Daughters to Undergo Female Genital Mutilation

Female genital mutilation (FGM) is still a common practice in many countries in Africa and the Middle East. Understanding the determinants of FGM can lead to more active interventions to prevent this harmful practice. The goal of this study is to explore factors associated with FGM behavior among Iranian mothers and their daughters. Based on Ajzen’s theory of planned behavior, we examined the predictive value of attitudes, subjective norms, perceived behavioral control and several socio-demographic variables in relation to mothers’ intentions to mutilate their daughters. A paper-and-pencil survey was conducted among 300 mothers (mean age = 33.20, SD = 9.09) who had at least one daughter and who lived in Ravansar, a county in Kermanshah Province in Iran. Structural equation modeling was used to investigate the relationships among the study variables. Our results indicate that attitude is the strongest predictor of mothers’ intentions to allow their daughters to undergo FGM, followed by subjective norms. Compared to younger mothers, older mothers have more positive attitudes toward FGM, perceive themselves as having more control over their behavior and demonstrate a greater intention to allow their daughter to undergo FGM. Furthermore, we found that less educated mothers and mothers living in rural areas had more positive attitudes toward FGM and feel more social pressure to allow FGM. The model accounts for 93 percent of the variance in the mothers’ intentions to allow their daughters to undergo FGM. Intervention programs that want to decrease FGM might focus primarily on converting mothers’ neutral or positive feelings toward FGM into negative attitudes and on alleviating the perceived social pressure to mutilate one’s daughter. Based on our findings, we provide recommendations about how to curtail mothers’ intentions to allow their daughters to undergo FGM.     

Getting a Fair Share: Attitudes and Perceptions of Biobank Stakeholders Concerning the Fairness of Sample Sharing

Biobanks are essential tools for furthering a broad range of medical research areas. However, despite the plethora of national and international laws and guidelines which apply to them, the access and sharing policies of biobanks are only sparsely addressed by regulatory bodies. The ‘give and take’ process of biosample sharing is largely left up to biobank stakeholders themselves to oversee; it is therefore both in stakeholders' power, and in their interest, to ensure that sample accessibility is fair. This is an important step in motivating researchers to collaborate and pool samples, and is crucial to fostering trust in the absence of universally accepted standard practices. To date, little attention has been paid to how fairness considerations affect scientific material sharing, and no empirical research has been carried out to determine the role that fairness plays in collaborative studies. In order to begin to gain understanding in this area, we interviewed 36 biobank stakeholders currently working in Switzerland, focusing on their perceptions of current and optimal fair sharing practices. Our findings reveal that fairness is an important feature of exchange situations for these stakeholders, and that they have well‐formed notions about the practical elements of fair sample access, although ideas about the concept of fairness itself are vague. In order to support efforts to network biobanks, attention should be paid to this issue to reassure all involved that they are getting a fair share in their cooperative efforts.     

Coordination of Initiation of Nuclear Division and Initiation of Cell Division in Schizosaccharomyces pombe: Genetic Interactions of Mutations

sep1⁺ encodes a Schizosaccharomyces pombe homolog of the HNF-3/forkhead family of the tissue-specific and developmental gene regulators identified in higher eukaryotes. Its mutant allele sep1-1 causes a defect in cytokinesis and confers a mycelial morphology. Here we report on genetic interactions of sep1-1 with the M-phase initiation mutations wee1⁻, cdc2-1w, and cdc25-22. The double mutants sep1-1 wee1⁻ and sep1-1 cdc2-1w form dikaryon cells at high frequency, which is due to nuclear division in the absence of cell division. The dikaryosis is reversible and suppressible by cdc25-22. We propose that the genes wee1⁺, cdc2⁺, cdc25⁺, and sep1⁺ form a regulatory link between the initiation of mitosis and the initiation of cell division.     

红毛菜丝状体核分裂研究

选择具异型世代交替的福建人工栽培的红毛菜为研究材料,对红毛菜丝状体世代的丝状藻丝及孢子囊枝等阶段进行了较系统的核分裂观察研究,探讨红毛菜核分裂特征.结果显示:红毛菜营养藻丝和孢子囊枝细胞均为二倍体细胞,2n=8,其核分裂显示为有丝分裂的过程;同时,丝状体阶段细胞核分裂至前期末均会出现同源染色体配对现象,显示有丝分裂同源染色体配对行为是红毛菜丝状体核分裂的一个重要特征.     

Nuclear Repulsion Enables Division Autonomy in a Single Cytoplasm

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Observations On Nuclear Division in vegetative hyphae of aquatic fungi

Summary Achlya aquatica, A. prolifera andA. racemosa are additional examples of fungi in whose vegetative mycelium, the nuclei do not divide in a manner directly comparable to ordinary mitosis. During division the entire nucleus, which consists of variously shaped chromatin and the nucleolus, becomes angular and elongates. The chromatin separates into two portions, which are situated at opposite ends of the elongating nucleus. As division proceeds the nuclei separate. Each sister nucleus sonsists of chromatin and a portion of the divided nucleolus. Spindless, chromosomal filaments or metaphase plates could not be observed during division.     

促绒毛生长基因及其在转基因动物中的应用

通过转基因克隆技术使得外源基因在皮肤细胞内超表达,进而促进毛囊发育和绒毛生长是培育高产量绒毛动物品系的有效途径.在转基因动物中构建真核表达栽体常用的皮肤特异性启动子主要是皮肤角蛋白基因启动子,具有促绒毛生长功能的基因则包括编码生长因子、转录因子及小分子蛋白的基因.目前已获得利用这些特异性启动子调控外源基因在皮肤细胞内超表达的转基因动物.