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At least 1,099 records · Page 61Linked to original sources
PubMed2006

Iridescent plumage in satin bowerbirds: structure, mechanisms and nanostructural predictors of individual variation in colour.

Iridescence is produced by coherent scattering of light waves from alternating layers of materials of different refractive indices. In birds, iridescent colours are produced by feather barbules when light is scattered from alternating layers of keratin, melanin and air. The structure and organization of these layers, and hence the appearance of bird species with different types of plumage iridescence, varies extensively. One principal distinction between different types of iridescent colours is whether they are produced by a single pair of layers or by multiple pairs of layers. Multi-layer iridescence, such as that displayed by hummingbirds, has been relatively well characterized, but single-layer iridescence has only recently been modeled successfully. Here we use electron microscopy, spectrometry and thin-film optical modeling to investigate the glossy, ultraviolet-blue iridescent plumage colouration of adult male satin bowerbirds Ptilonorhynchus violaceus minor. The flattened barbules of adult males are composed of a superficial keratin layer overlying a melanin layer that is several granules thick. A thin-film model based on the thickness of the keratin layer and its two associated interfaces (air/keratin and keratin/melanin) generates predicted reflectance spectra that closely match measured spectra. In addition, hues predicted from this model are positively correlated with measured hues. As predicted from our thin-film model, measured hues shifted to shorter wavelengths at increasing angles of incidence and reflectance. Moreover, we found that individual variation in barbule nanostructure can predict measured variation in both hue and UV-chroma. Thus, we have characterized the microstructure of satin bowerbird barbules, uncovered the mechanisms responsible for producing ultraviolet iridescence in these barbules, and provided the first evidence of a nanostructural basis for individual variation in iridescent plumage colour.

Animals↗
PubMed1984

[Action of UV radiation on the surface of mammalian immunocompetent cells. III. Ultrastructural changes in the glycocalyx of mouse lymphocytes].

The outer perimembrane layer of murine spleen lymphocytes were studied with electron microscopy. Mice were treated with short-wave (254 nm) and long-wave (365 nm) ultraviolet radiation in isoeffective lethal doses. The other perimembrane layers were stained with Alcian blue and Ruthenium red. The 254 nm UV treatment decreased the level of dye--sorption by these perimembrane layers, whereas no such effect was obvious after the 365 nm UV treatment.

Animals↗
PubMedDate not supplied

Dyke Award. Europium-DTPA: a gadolinium analogue traceable by fluorescence microscopy.

A lanthanide series chelate, europium(Eu)-DTPA, was synthesized to serve as a histochemical analogue for the widely used MR contrast agent gadolinium(Gd)-DTPA. Eu and Gd, being neighboring elements on the periodic table, share many fundamental properties, including ionic radius, valence, and chemical reactivity. Eu-DTPA, however, possesses one important physical property not shared by Gd-DTPA: luminescence under ultraviolet light. The feasibility of detecting Eu-DTPA in animal tissues under fluorescence microscopy was systematically evaluated and documented. Distinctive orange-red luminescence of Eu-DTPA could be observed in the kidneys, livers, dura, choroid, and pituitary glands of rats after intravascular injection. No luminescence was detected in areas of brain beyond an intact blood-brain barrier. When the brain was locally injured by an experimental laceration, however, leakage of Eu-DTPA was detected. Electron probe microanalysis confirmed the parallel presence or absence of simultaneously injected Eu-DTPA and Gd-DTPA in all tissues studied. Fluorescence microscopy with Eu-DTPA has thus been validated as a method for tracing the distribution of Gd-DTPA at the microscopic level.

Animals↗
PubMed1982

Localization of Legionella pneumophila in tissue using FITC-conjugated specific antibody and a background stain.

Lightly staining formalin-fixed or fresh tissue with Gram's crystal violet obviates interfering nonspecific fluorescence by acting as a metachromatic stain in ultraviolet light. Against the easily recognized background of tissues and cells fluorescein isothiocyanate-tagged Legionella pneumophila antibodies can then identify this bacterium in or on individual cells. This procedure can be run at room temperature in two hours and has the potential for further widespread applicability.

Animals↗
PubMed1992

Electron microscopic study of (A)BC excinuclease. DNA is sharply bent in the UvrB-DNA complex.

Nucleotide excision repair in Escherichia coli is initiated by the UvrA, UvrB and UvrC proteins. UvrA is the damage recognition subunit, makes an A2B1 complex with the targeting subunit UvrB, and the complex binds to the lesion site; UvrA dissociates leaving behind a very stable UvrB-DNA complex that is recognized by the trigger subunit, UvrC, and the ensuing UvrB-UvrC heterodimer makes two incisions, one on either side of the lesion. Using electron microscopy, we investigated the structures of these early A, A-B intermediates on DNA containing ultraviolet light photoproducts. UvrA, which is known to bind to DNA as a dimer and produce a DNase I footprint of 33 base-pairs does not change the trajectory of DNA appreciably. The A2B1 complex clearly shows a bipartite structure and its effect on the trajectory of the DNA was not consistently straight or kinked. In contrast, the DNA in the preincision UvrB-DNA complex appears to be severely kinked; 43% of the molecules are bent by 80 degrees or more, with an average bending angle of 127 degrees. It appears that protein-induced bending is an important step on the pathway leading to excision of the damaged nucleotide by (A)BC excinuclease.

Adenosine Triphosphatases↗
PubMed1980

The microscopical structure and quantitative changes of pituitary cell populations in frogs (Rana esculenta L.) irradiated by ultraviolet light.

The percentage of cell populations of hypophysis pars distalis, their ultrastructure, degranulation phenomena and volume of cell nuclei easured by karyometry was examined in frogs, Rana esculenta L. irradiated by UV light. The observed changes, reflecting alterations of the secretory activity were most prominent in B2 cells producing gonadotropic hormones and in B3 cells probably responsible for the secretion of ACTH. A concomitant increase of the number of chromophobic cells was observed. The obtained results are discussed in relation to data from the existing literature.

Adrenocorticotropic Hormone↗
PubMed1983

Damage of the cornea epithelium caused by ultraviolet radiation. A scanning electron microscopic study in rabbit.

Rabbit cornea epithelium was exposed to UV-radiation for 15 min from a distance of 50 cm, and specimens were studied after 1/2, 1, and 3 h, respectively. The following changes occurred: 1) Reduced number of the large impressions or the full-thickness holes of the superficial cells. 2) Partly rejected cells. 3) Numerous small plasma membrane defects. This investigation shows plasma membrane defects at an early stage after the exposure, and this may be the locus for the initial damage.

Animals↗
PubMed2004

Effects of UV-A irradiation on lens morphology and optics.

Epidemiological studies have indicated that ultraviolet radiation (UVR) is one of the main factors leading to senile cataract formation. We investigated morphological changes in the eye lens caused by UVR-A. Twenty three pairs of lenses obtained from 23 one-year-old calves were used for this study. For each pair, one lens was exposed to 44 J/m(2) UVR in the 365 nm wavelength region while the contralateral lens was not exposed and served as a control. The lenses were placed in specially designed organ culture containers for pre-incubation. Lenses were exposed to UVR after one day in culture. After irradiation, lens optical quality was monitored throughout additional 15 days of the culture period and lenses were taken for morphological analysis by scanning electron microscopy. Damage to lens optical quality was evident as early as day 8 after the irradiation and increased with time in culture. We found irregularity of fiber morphology in lenses exposed to UV-A irradiation (but not in control lenses), similar to that reported previously for aged lenses. At the end of the culture period (day 16), lens fiber membranes also showed holes in fiber membranes. We conclude that UVR-A caused damage to cell membranes of the lens and alterations in lens optics, which may subsequently lead to senile cataract formation.

Animals↗
PubMed1972

Isolation and characterization of subacute sclerosing panencephalitis virus nucleocapsids.

Nucleocapsids from subacute sclerosing panencephalitis (SSPE) virus-infected CV-1 cells were concentrated by differential centrifugation employing sucrose cushion techniques and further purified by centrifugation through a linear CsCl density gradient. The bouyant density of (3)H-uridine-labeled nucleocapsids in CsCl was found to be 1.31 g/cm(3). Ultraviolet absorption spectra of the purified SSPE nucleocapsid showed an absorption maximum at 260 to 265 nm and a 280/260 ratio that corresponded to a nucleic acid content of approximately 4.3%. Negatively stained preparations of SSPE nucleocapsids were found to have a width of 18 +/- 1 nm, a periodicity of 5 to 6 nm, and a length between 1-1.4 mum, with the greatest number at 1.3 mum.

Animals↗
PubMed2005

Effect of packing on orientation and cis-trans isomerization of azobenzene chromophore in Langmuir-Blodgett film.

Photoactive film material of long-chain azobenzene derivative, p-(omega-trimethylammoniodecyloxy)-p'-octyloxyazobenzene bromide (TAOAB), was fabricated into a Langmuir-Blodgett (LB) film by a polyion-complex technique using poly(sodium 4-styrenesulfonate) as a polyanion. To investigate the effect of the packing state of the azobenzene chromophore on its orientation and cis-trans isomerization, TAOAB was mixed with methyl stearate in the LB film matrix at various mole fractions (X(TAOAB)), and structural characterizations were subsequently carried out by means of Fourier transform infrared and ultraviolet-visible spectroscopies, X-ray diffraction analysis, and atomic force microscopy. The results obtained show that as the degree of packing increases, both the azobenzene chromophores and the hydrocarbon chains orient more perpendicularly to the surface of the LB film. In addition, reversible cis-trans photoisomerization of TAOAB took place upon alternate irradiation with UV and visible light even in a mixed LB film with the chromophores in a dense lateral packing state. In the process of thermal cis-to-trans isomerization, we found that the reaction rate is strongly affected by the packing state of TAOAB at 20 degrees C, reflecting the differences in steric hindrance among LB films of various X(TAOAB). In addition, higher activation energy was obtained for thermal cis-to-trans isomerization when the free volume around the chromophores became smaller.

Journal Article↗
PubMed2006

Close-packed hemispherical microlens array from two-dimensional ordered polymeric microspheres.

This paper describes a facile, reproducible soft-lithography-based method for fabricating hexagonally close-packed microlens arrays by templating the surface of a colloidal monolayer, which is formed by spin-casting monodisperse polystyrene microspheres. The relief structure of colloidal monolayers has successfully generated PDMS elastomers with hexagonal arrays of hemispherical air voids. Closely packed hemispherical microlens arrays were imprinted on ultraviolet-curable photopolymers which are bound on glass substrates. Atomic force microscopy measurements showed that each spherical hole of the PDMS molds is 103 nm deep and the replicated microlens is 95 nm in height with narrow size distribution and good reproducibility. Without a multistep engineering process, this method might provide a reliable route to fabricate embossed thin layers ranging from nanometer to micrometers by controlling the size of polymer microspheres over a centimeter scale area.

Journal Article↗
PubMed1989

Fine-structural aspects of bromodeoxyuridine incorporation in sister chromatid differentiation and replication banding.

The structure of harlequin-stained chromosomes following substitution with low levels of 5-bromodeoxyuridine (BrdUrd) over two cell cycles and high levels over the last part of one cycle (replication banding) was studied in Chinese hamster ovary (CHO) cells. By using correlative light (LM) and scanning electron microscopy (SEM), it was shown that the effects of both the ultraviolet light (u.v.) and hot SSC treatment steps of the harlequin staining procedure were necessary to obtain sister-chromatid differentiation (SCD) or replication banding. u.v. treatment alone resulted in dark Giemsa staining of both chromatids with SEM morphology of short compact protuberances and an overall flattened smooth appearance in both the unsubstituted and BrdUrd-substituted chromatids, a morphology essentially similar to that of untreated chromosomes. SSC alone on the other hand resulted in dark-staining chromatids with an SEM morphology of raised, loosely packed loops of fibres in both types of chromatids. u.v. and SSC treatment together resulted in differentiation, with dark-staining unifilarly (TB) chromatids in the LM corresponding to raised loosely packed loops in the SEM and pale bifilarly (BB) chromatids corresponding to the smooth compact flattened SEM appearance. Where the BrdUrd-substituted strand became the template (BT), or when the nascent strand TB contained high levels of BrdUrd substitution in replication banding, the chromatid stained pale and showed the compact smooth appearance in the SEM. The Giemsa staining ability and ultrastructural morphology of harlequin staining is discussed with respect to putative DNA loss and also in terms of preferential protein-protein, protein-DNA cross-linkage in BrdUrd-containing DNA. These changes are also compared with the ultrastructural morphology observed after other banding methods, where deterioration of protein and DNA-protein interaction resulting in aggregation of chromatin fibres appears to be the major mechanism.

Animals↗
PubMed2004

Highly coherent light at 13 nm generated by use of quasi-phase-matched high-harmonic generation.

By measuring the fringe visibility in a Young's double pinhole experiment, we demonstrate that quasi-phase-matched high-harmonic generation produces beams with very high spatial coherence at wavelengths around 13 nm. To our knowledge these are the highest spatial coherence values ever measured at such short wavelengths from any source without spatial filtering. This results in a practical, small-scale, coherent, extreme-ultraviolet source that is useful for applications in metrology, imaging, and microscopy.

Journal Article↗
PubMed1997

1,25-dihydroxyvitamin D3, transforming growth factor beta1, calcium, and ultraviolet B radiation induce apoptosis in cultured human keratinocytes.

Apoptosis is a cellular process of self-directed suicide that plays a key role during morphogenesis and in the maintenance of homeostasis in continuously renewing tissues. Currently, apoptosis is detected mainly by gel electrophoresis of fragmented DNA and by typical ultrastructural features such as cell shrinkage and chromatin condensation. Recently, an in situ technique was developed that allows the detection of the apoptotic process in cells and the quantitation of apoptosis in cell populations. We applied this technique to evaluate the apoptotic process in cultured normal human keratinocytes under basic conditions and after stimulation with factors and agents that are presumed but have never been proved to induce apoptosis in these cells. Apoptosis was analyzed after stimulation with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], transforming growth factor beta1 (TGFbeta1), calcium, UVB, or tumor necrosis factor alpha (TNFalpha). All these factors except TNFalpha induced apoptosis in human keratinocytes. Whereas UVB and calcium were good apoptogenic stimuli at 6 and 24 h, respectively, the vitamin D derivative and TGFbeta1 induced apoptosis after 5 and 6 d in culture. Apoptosis was also established by DNA fragmentation and electron microscopy. Finally, TUNEL technique showed that the number of apoptotic cells increases slightly (5-10%) from 24 to 144 h even in untreated keratinocytes. Our studies indicate that factors normally involved in the regulation of cell growth and differentiation can also control apoptosis.

Apoptosis↗