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The timing of the formation and usage of replicase clusters in S-phase nuclei of human diploid fibroblasts
The sites of nascent DNA synthesis were compared
with the distribution of the proliferating cell nuclear antigen (PCNA) in S-phase nuclei of human diploid fibroblasts (HDF) by two in vitro techniques. Firstly, proliferating fibroblasts growing in culture that had been synchronised at S-phase were microinjected with the thymidine analogue biotin-11-dUTP. The sites of incorporation of biotin into injected cells
were compared with the distribution of PCNA by
indirect immunofluorescence microscopy and laser
scanning confocal microscopy (LSCM). In common
with other studies, a progression of patterns for both biotin incorporation and PCNA localisation was observed. However, we did not always observe
coincidence in these patterns, the pattern of biotin incorporation often resembling the expected, preceding distribution of PCNA. In nuclei in which the pattern of biotin incorporation appeared to be identical to the distribution of PCNA, LSCM revealed that not all of the sites of PCNA immunofluorescence were incorporating biotin at the same time. Secondly,
nuclei which had been isolated from quiescent
cultures of HDF were innoculated into cell-free
extracts of Xenopus eggs which support DNA replication in vitro. Following innoculation into these extracts DNA replication was initiated in each nucleus. The sites of DNA synthesis were detected by biotin-11-dUTP incorporation and compared with the distribution of PCNA by indirect immunofluorescence. Only a single pattern of biotin incorporation and PCNA distribution was observed. PCNA accumulated
at multiple discrete spots some 15min before any biotin incorporation was observed. When biotin incorporation did occur, LSCM revealed almost complete coincidence between the sites of DNA synthesis and the sites at which PCNA was localised.Brunel Open Access Publishing Fun
The Effect of Fractal Contact Lenses on Peripheral Refraction in Myopic Model Eyes
Purpose: To test multizone contact lenses in model eyes: Fractal Contact Lenses (FCLs), designed to induce
myopic peripheral refractive error (PRE).
Methods: Zemax ray-tracing software was employed to simulate myopic and accommodation-dependent model
eyes fitted with FCLs. PRE, defined in terms of mean sphere M and 90–180 astigmatism J180, was computed at
different peripheral positions, ranging from 0 to 35 in steps of 5, and for different pupil diameters (PDs).
Simulated visual performance and changes in the PRE were also analyzed for contact lens decentration and
model eye accommodation. For comparison purposes, the same simulations were performed with another
commercially available contact lens designed for the same intended use: the Dual Focus (DF).
Results: PRE was greater with FCL than with DF when both designs were tested for a 3.5 mm PD, and with and
without decentration of the lenses. However, PRE depended on PD with both multizone lenses, with a
remarkable reduction of the myopic relative effect for a PD of 5.5 mm. The myopic PRE with contact lenses
decreased as the myopic refractive error increased, but this could be compensated by increasing the power
of treatment zones. A peripheral myopic shift was also induced by the FCLs in the accommodated model eye.
In regard to visual performance, a myopia under-correction with reference to the circle of least confusion
was obtained in all cases for a 5.5 mm PD. The ghost images, generated by treatment zones of FCL, were
dimmer than the ones produced with DF lens of the same power.
Conclusions: FCLs produce a peripheral myopic defocus without compromising central vision in photopic
conditions. FCLs have several design parameters that can be varied to obtain optimum results: lens diameter,
number of zones, addition and asphericity; resulting in a very promising customized lens for the treatment
of myopia progression.This research was supported by the Ministerio de Economia y Competitividad (grant FIS2011-23175), the Generalitat Valenciana (grant PROMETEO2009-077) and the Universitat Politecnica de Valencia (grant INNOVA SP20120569), Spain.Rodríguez Vallejo, M.; Benlloch Fornés, JI.; Pons Martí, A.; Monsoriu Serra, JA.; Furlan, WD. (2014). The Effect of Fractal Contact Lenses on Peripheral Refraction in Myopic Model Eyes. Current Eye Research. 39(12):1-10. https://doi.org/10.3109/02713683.2014.903498S110391
Estimating the Production Function for Human Capital: Results from a Randomized Controlled Trial in Colombia
Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU
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The A- and B-type cyclins of Drosophila are accumulated and destroyed in temporally distinct events that define separable phases of the G2-M transition.
We show that the sequence of Drosophila cyclin B has greater identity with B-type cyclins from other animal phyla than with Drosophila cyclin A, suggesting that the two cyclins have distinct roles that have been maintained in evolution. Cyclin A is not detectable in unfertilized eggs and is present at low levels prior to cellularization of the syncytial embryo. In contrast, the levels of cyclin B remain uniformly high throughout these developmental stages. In cells within cellularized embryos and the larval brain, cyclin A accumulates to peak levels in prophase and is degraded throughout the period in which chromosomes are becoming aligned on the metaphase plate. The degradation of cyclin B, on the other hand, does not occur until the metaphase-anaphase transition. In cells arrested at c-metaphase by treating with microtubule destabilizing drugs to prevent spindle formation, cyclin A has been degraded in the arrested cells, whereas cyclin B is maintained at high levels. These observations suggest that cyclin A has a role in the G2-M transition that is independent of spindle formation, and that entry into anaphase is a key requirement for the degradation of cyclin B
A conserved mitotic kinase active at late anaphase—telophase in syncytial Drosophila embryos
Xpd/Ercc2 regulates CAK activity and mitotic progression
General transcription factor IIH (TFIIH) consists of nine sub- units: cyclin-dependent kinase 7 (Cdk7), cyclin H and MAT1 (forming the Cdk-activating-kinase or CAK complex), the two helicases Xpb/Hay and Xpd, and p34, p44, p52 and p62 (refs 1–3). As the kinase subunit of TFIIH, Cdk7 participates in basal transcription by phosphorylating the carboxy-terminal domain of the largest subunit of RNA polymerase II1,4,5. As part of CAK, Cdk7 also phosphorylates other Cdks, an essential step for their activation6–9. Here we show that the Drosophila TFIIH com- ponent Xpd negatively regulates the cell cycle function of Cdk7, the CAK activity. Excess Xpd titrates CAK activity, resulting in decreased Cdk T-loop phosphorylation, mitotic defects and lethality, whereas a decrease in Xpd results in increased CAK activity and cell proliferation. Moreover, Xpd is downregulated at the beginning of mitosis when Cdk1, a cell cycle target of Cdk7, is most active. Downregulation of Xpd thus seems to contribute to the upregulation of mitotic CAK activity and to regulate mitotic progression positively. Simultaneously, the downregulation of Xpd might be a major mechanism of mitotic silencing of basal transcription
Dynamic wettability of pHEMA-based hydrogel contact lenses
Standard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film