Papers by Helvia Rosa Pelayo Benavides
Planta, 2001
Under long hydroxyurea treatments, evidence was obtained for the sequential activation of four ch... more Under long hydroxyurea treatments, evidence was obtained for the sequential activation of four checkpoints located between the onset of S phase and mitosis in Allium cepa L. root meristems. Biparametric flow cytometry (Br-DNA/total DNA) showed that cells initially accumulated at early S phase but, after a delay, they resumed replication and paused again at mid S phase. Cells not only overrode this second replication block but also any G2 checkpoint they encountered. Thus, a late mitotic wave was produced in the presence of hydroxyurea. The wave was formed by cells that had apparently completed their replication (normal mitoses), while others displayed anaphases/telophases with less than the expected DNA content and with chromosomal breaks (aberrant mitoses). The presence of aberrant mitoses is direct evidence for the undue override of the two G2 checkpoints responsible for surveillance of completion of DNA synthesis and repair, respectively. Caffeine selectively abrogated the G2 block produced by the checkpoint that controls post-replication DNA repair, as it advanced the entry of cells into an aberrant mitosis. However, caffeine proved not to be the universal checkpoint-evading agent as postulated. Caffeine did not modify the spontaneous override of the replication checkpoints. Moreover, it seems to enforce the checkpoint that controls the completion of DNA synthesis, as the appearance of the late wave of normal mitoses produced in the presence of hydroxyurea was prevented by the use of caffeine.
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Plant Physiology and Biochemistry, 2005
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Journal of Cell Science, 2002
Mitotic progression is timely regulated by the accumulation and degradation of A- and B-type cycl... more Mitotic progression is timely regulated by the accumulation and degradation of A- and B-type cyclins. In plants, there are three classes of A-, and two classes of B-type cyclins, but their specific roles are not known. We have generated transgenic tobacco plants in which the ectopic expression of a plant cyclin B2 gene is under the control of a tetracycline-inducible promoter. We show that the induction of cyclin B2 expression in cultured cells during G2 phase accelerates the entry into mitosis and allows cells to override the replication checkpoint induced by hydroxyurea in the simultaneous presence of caffeine or okadaic acid, drugs that are known to alleviate checkpoint control. These results indicate that in plants, a B2-type cyclin is a rate-limiting regulator for the entry into mitosis and a cyclin B2-CDK complex might be a target for checkpoint control pathways. The cyclin B2 localization and the timing of its degradation during mitosis corroborate these conclusions: cyclin B...
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Environmental and Experimental Botany, 2009
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Biological Research, 2003
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La cancelacion de las rutas de chequeo por analogos de purinas y, en particular, la induccion de ... more La cancelacion de las rutas de chequeo por analogos de purinas y, en particular, la induccion de la entrada indebida en mitosis de celulas detenidas en la fase S son fenomenos basicamente descritos en celulas animales transformadas. Las celulas vegetales comparten con otros organismos eucarioticos tanto la maquinaria del ciclo como varias rutas de chequeo susceptibles de cancelacion por analogos de purinas. Con esto en mente, se evaluo la respuesta a hidroxiurea y/o cafeina en dos modelos vegetales con complemento diploide integro: los meristemos radicales de AIlium cepa L. y celulas en cultivo de Nicotiana fabacum L. que eran transgenicas para el gen de la cicliia mitotica de alfalfa. Se determino el efecto de estas drogas sobre indices mitoticos y crecimiento celular en celulas sincronicas marcadas como binucleadas. Al mismo tiempo, se evaluo su efecto sobre las diferentes subperiodos de la interfase en las celulas nativas, asincronicas, mediante citometria de flujo. Mediante este...
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European Journal of Cell Biology
The present work shows that replication of the 5 S ribosomal genes differs in time and 3'deox... more The present work shows that replication of the 5 S ribosomal genes differs in time and 3'deoxyadenosine sensitivity from replication of other nuclear genes, in Allium cepa L. root meristems. Fluorescence in situ hybridization with the pTa794 DNA probe which contains a complete 410 bp 5 S gene from Triticum aestivum allowed to detect four clusters of 5 S genes in these diploid cells (2n = 16), two of them in the short arm of the smallest metacentric chromosomal pair 7. Replication of the 5 S ribosomal genes occurred very early in interphase, as discerned by their resolution as doubled spots only two hours after interphase was initiated in synchronous binucleate cells. Codetection of nuclear replication (by immunodetection of 5-bromo-2'-deoxyuridine incorporation) showed that the replication of the 5 S ribosomal genes occurred before any incorporation of 5-bromo-2'deoxyuridine could be detected in the nuclei. The earliest Br-DNA detected in these cells followed a radial pa...
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Papers by Helvia Rosa Pelayo Benavides