1,720,973 research outputs found
Flow cytometry, sorting and immunocharacterization with proliferating cell nuclear antigen of cycling and non-cycling cells in synchronized pea root tips
No full textIn the 3-d-old 2-mm root tip of Pisum sativum L. cv. Lincoln the percentage of actively proliferating cells is estimated to be 70%. The remaining cells are non-cycling and arrested with 2C and 4C DNA content in G0 and in G2Q, respectively. In this work we studied the kinetic significance of these quiescent cells, using the sorting capabilities of flow cytometry and immunofluorescence techniques to detect the proliferation marker PCNA (proliferating cell nuclear antigen) inside cells within the different cell-cycle compartments. While in animal cells, PCNA is present at a high level only in actively proliferating cells, in 3-d-old pea root tips 95% of the cells are PCNA-positive. After flow cytometry and sorting of pea non-cycling nuclear populations, all G2Q nuclei appeared strongly PCNA-positive, indicating that these cells had recently left the cell cycle. By contrast, most G0 nuclei showed a low level of PCNA immunofluorescence intensity, as measured by image analysis, with about 25% of the nuclei being PCNA-negative. This small percentage was found to correspond to root cap cells, as could be observed in the root tip section. These are the only cells in the root apical region which are fully differentiated and which, therefore, lack the competence to enter the cell cycle. In contrast, the more or less PCNA-positive G0 nuclei could represent a kinetically heterogeneous population of cells competent to proliferate, but which have either recently left the cell cycle or are progressing to the G0-G1 transition
Cyclin-dependent kinase-like proteins in pea nuclei: their presence and role in cell proliferation
No full textAlthough many putative cdk (cyclin-dependent kinase) homologue genes have been identified in higher plants, their function and involvement in cell proliferation are still unclear. In this work we investigated the presence and distribution of cdk-like proteins in root tip meristem nuclei at different germination times (before, during, and after the onset of cell proliferation) and in nuclei of differentiated leaves. Nuclear cdk-like proteins were found in the root meristem throughout seed germination with a higher amount in actively proliferating cells, but were not detected in differentiated leaf. Characterization of the detected pea cdk-like proteins by immunoblotting led to the identification of two specific principal proteins of 33.2 and 34 kDa with the cdk conserved motif PSTAIRE. The p33.2 protein was also recognized by the anti-human p33(cdk2) antibody, suggesting that the p33.2 and p34 proteins could be pea homologues of human p33(cdk2) and p34(cdk1), involved in the G(1)-S and G(2)-M transitions, respectively. Additional analysis of pea cdk protein localization has shown partial localization of these proteins at DNA replication sites during the G(1) to S transition. These microscopical and biochemical data support the hypothesis that, in pea nuclei as in mammals, many PSTAIRE-cdks are present with different functions related to cell proliferation, one of which is probably involved in the control of the G(1)-S transition
The presence of a p53-like protein during pea seed maturation and germination
No full textThe mechanisms that allow monitoring of DNA damage and the activation of repair systems in plants are poorly known. In mammalian cells the tumor suppressor protein p53 plays an important role in the checkpoint pathway induced by DNA damage. In this work, me investigated the presence and distribution of the p53-like protein in pea root tip nuclei and its role during early germination in relation to DNA damage. In pea seed, PFGE and TdT assays show that DNA fragmentation occurs during maturation and dry seed storage, and that this DNA fragmentation is repaired at the beginning of germination before the onset of proliferation. In the same seeds, the p53-like protein was found during maturation and germination. Immunoblotting characterization of this protein led to the identification of a single specific protein of about 94 kDa, more abundant at the beginning of the hydration process than in actively cycling cells. Furthermore, the p53-like protein revealed different nuclear distribution patterns, probably in relation to the formation of DNA fragments in dry seeds, and to the reactivation of repair mechanisms during early germination. These data suggest that the presence of a p53-like protein in quiescent or proliferating, pea embryo is related to DNA damage, and serves for the maintenance of genetic information and the development of normal seedlings
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Analisi della variabilità genetica di S. Tombeanensis attraverso marcatori molecolari del DNA
No full textIsolation and characterization of two cyclin cDNAs from Pisum sativum L.
No full textIn order to investigate the role of cell division in plant development, we isolated two plant genes which encode homologues of animal and yeast cell cycle regulators known as cyclins. Through the use of degenerate primers and the polymerase chain reaction (PCR) we isolated a Pisum sativum sequence which showed homology to the ‘cyclin box°s functional domain found within cyclin proteins. Using this sequence as probe we isolated two different cyclin cDNAs, Pissa;CycA3;1 and Pissa;CycB1;3 from a Pisum sativum L. root tip cDNA library. The deduced amino acid sequences of both cDNAs showed the highest sequence similarity with mitotic cyclins. Analyses of Pissa;CycA3;1 and Pissa;CycB1;3 expression in different tissues, by reverse transcription-polymerase chain reaction (RT-PCR) using primers corresponding to unique regions of their cDNAs, showed their differential expression in relation to cell cycle activity. Furthermore, RT-PCR was used to analyze synchronized root tip cells; results revealed that Pissa;CycA3;1 is preferentially expressed in mid-S (SM) and during late S-G2 (Sl- G2) transition, whereas Pissa;CycB1;3 mRNA is only detectable in Sl and G2 phases
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