Papers by S. Monajembashi
Berichte der Bunsengesellschaft für physikalische Chemie
ABSTRACT
Optical Trapping and Optical Micromanipulation VI, 2009
One essential cause of human ageing is the accumulation of DNA damages during lifetime. Experimen... more One essential cause of human ageing is the accumulation of DNA damages during lifetime. Experimental studies require quantitative induction of damages and techniques to visualize the subsequent DNA repair. A new technique, the "immuno fluorescent comet assay", is used to directly visualize DNA damages in the microscope. Using DNA repair proteins fluorescently labeled with green fluorescent protein, it could be
Journal of cell science, 1987
An ultraviolet-laser microbeam was shown to be suitable for inducing fusion of individually selec... more An ultraviolet-laser microbeam was shown to be suitable for inducing fusion of individually selected plant protoplasts or of B-lymphocytes with myeloma cells. The fusion took place in normal culture medium and the fusogenic condition perturbed the cells only for a fraction of a millisecond. Without manipulating the cell culture except for exposing the cells to laser light, fusion products between preselected individual pairs may be produced.
Cytometry, 1991
Optical tweezers, based on a compact diode pumped Nd:YAG laser providing 350 mW at 1,064 nm coupl... more Optical tweezers, based on a compact diode pumped Nd:YAG laser providing 350 mW at 1,064 nm coupled into a Zeiss IM 35 microscope, were used to sort CD4+ T cells into a capillary for further mechanical handling and to establish contact between single human natural killer (NK) cells and human erythroleukemia cells (K562) as targets. After contact and a lag phase of a few tens of seconds, the target cell starts to change its morphology and membrane blebbing occurs. The kinetics of the attack of the NK cell on K562 cells is not straightforward but governed by temporal oscillations in the shape of the target cell (zeosis). In a second application, the optical tweezers are combined with a UV laser microbeam based on a pulsed UV laser and with flow cytometry and sorting. With the pulsed laser, segments of sorted chromosome 1 of the chinese hamster karyotype (CHV 79) can be easily micro-dissected and subsequently collected using the optical tweezers. This allows preparation of a few hundre...
Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues V, 2007
There has been considerable current interest in rotational behavior of red blood cells (RBC) in o... more There has been considerable current interest in rotational behavior of red blood cells (RBC) in optical tweezers. However, the mechanism of rotation in polarized tweezers is still not well understood and there exists conflicts in the understanding of this phenomenon. Therefore, we re-examined the underlying phenomenon by use of confocal fluorescence microscopy. Under different osmolarities of the buffer, the three dimensionally reconstructed images showed that the trapped RBC maintains its discotic shape and is oriented in vertical direction. Using dual optical tweezers, the RBC could also be oriented three-dimensionally in a controlled manner. Since, no folding of the RBC was observed under optical trapping beam, the rotational mechanism based on optical birefringence caused by folding of RBC can be ruled out. The alignment of RBC with polarization of the tweezers beam can be attributed to its formbirefringence. We also present the mechanism for possible rotational behavior of RBC in circularly polarized beam.
There has been considerable current interest in rotational behavior of red blood cells (RBC) in o... more There has been considerable current interest in rotational behavior of red blood cells (RBC) in optical tweezers. However, the mechanism of rotation in polarized tweezers is still not well understood and there exists conflicts in the understanding of this phenomenon. Therefore, we re-examined the underlying phenomenon by use of confocal fluorescence microscopy. Under different osmolarities of the buffer, the three dimensionally reconstructed images showed that the trapped RBC maintains its discotic shape and is oriented in vertical direction. Using dual optical tweezers, the RBC could also be oriented three-dimensionally in a controlled manner. Since, no folding of the RBC was observed under optical trapping beam, the rotational mechanism based on optical birefringence caused by folding of RBC can be ruled out. The alignment of RBC with polarization of the tweezers beam can be attributed to its formbirefringence. We also present the mechanism for possible rotational behavior of RBC in circularly polarized beam.
Applied Physics B, 2000
. In confocal laser scanning microscopes (CLSMs), lasers can be used for image formation as wel... more . In confocal laser scanning microscopes (CLSMs), lasers can be used for image formation as well as tools for the manipulation of microscopic objects. In the latter case, in addition to the imaging lasers, the light of an extra laser has to be focused into the object plane of the CLSM, for example as optical tweezers. Imaging as well as
Cytometry, 1999
Single-molecule studies in the life sciences often deal with observation or spectroscopy. Studies... more Single-molecule studies in the life sciences often deal with observation or spectroscopy. Studies of reactions are rare, and the light microscope has been used for such experiments only occasionally. In an experimental environment, for example, as is required for most nearfield scanning or electron microscopies, it is difficult to study single-molecule reactions of biological relevance. Therefore, we have developed techniques to study single-molecule reactions with classic (nonscanning) farfield light microscopy. The conversion of nicotinamide adenine dinucleotide (NAD+) and lactate to NADH (a reduced form of NAD+), pyruvate, and H+ catalyzed by a few LDH-1 enzyme molecules has been studied in substrate solutions with different viscosity using the NADH autofluorescence. It is even possible to monitor the progress of the reaction by phase-contrast microscopy via scattering or absorption by product molecules. As an example for a single-molecule reaction with a macromolecule as substrate, the handling and enzymatic cutting of fluorescently stained lambda-DNA is studied. In solutions containing 10 mM magnesium and 66 mM potassium ions at pH 7.9, an individual DNA molecule tends to collapse into a globular structure. When moved through an aqueous solution, it becomes stretched by viscosity drag. After stopping the motion, the molecule collapses and the dynamics of this process can be quantified. When a restriction enzyme is present, sequence-specific cutting can be directly observed in the light microscope. The theoretical restriction pattern, as predicted from the sequence of the molecule, can be generated directly under visual inspection.
Surface and Interface Analysis, 1997
ABSTRACT
Scandinavian Journal of Gastroenterology, 1988
Total RNA and mRNA were prepared from cystic fibrosis (CF) and control nasal polyps and nasal epi... more Total RNA and mRNA were prepared from cystic fibrosis (CF) and control nasal polyps and nasal epithelial cells. Genomic clones from the chromosomal region of the CF locus were screened by northern blots. A representative cDNA library from nasal polyps was cloned in the vector lambda gt10. For the construction of a physical genomic map around the CF locus single gene markers were isolated from metaphase 1:7q2qter chromosomes by laser micro-dissection and subsequent microcloning. A linkage study with the polymorphic markers met-H, met-D, and pJ3.11 was performed in 53 German CF families with at least 2 children. No significant correlation of any haplotype on the CF chromosomes with the clinical severity of the course of the disease could be observed, which provides evidence that cystic fibrosis is genetically homogeneous.
Radiation Research, 2002
DNA damage induced in NC37 lymphoblasts by optical tweezers with a continuous-wave Ti:sapphire la... more DNA damage induced in NC37 lymphoblasts by optical tweezers with a continuous-wave Ti:sapphire laser and a continuous-wave Nd:YAG laser (60-240 mW; 10-50 TJ/m2; 30-120 s irradiation) was studied with the comet assay, a single-cell technique used to detect DNA fragmentation in genomes. Over the wavelength range of 750-1064 nm, the amount of damage in DNA peaks at around 760 nm, with the fraction of DNA damage within the range of 750-780 nm being a factor of two larger than the fraction of DNA damage within the range of 800-1064 nm. The variation in DNA damage was not significant over the range of 800-1064 nm. When the logarithm of damage thresholds measured in the present work, as well as values reported previously in the UV range, was plotted as a function of wavelength, a dramatic wavelength dependence became apparent. The damage threshold values can be fitted on two straight lines, one for continuous-wave sources and the other for pulsed sources, irrespective of the type of source used (e.g. classical lamp or laser). The damage threshold around 760 nm falls on the line extrapolated from values for UV-radiation-induced damage, while the data for 800-1064 nm fall on a line that has a different slope. The change in the slope between 320 and 340 nm observed earlier is consistent with a well-known change in DNA-damaging mechanisms. The change observed around 780 nm is therefore suggestive of a further change in the mechanism(s). The data from this work together with our previous measurements provide, to the best of our knowledge, the most comprehensive view available of the DNA damage produced by microfocused light.
PLoS ONE, 2007
Albeit silks are fairly well understood on a molecular level, their hierarchical organisation and... more Albeit silks are fairly well understood on a molecular level, their hierarchical organisation and the full complexity of constituents in the spun fibre remain poorly defined. Here we link morphological defined structural elements in dragline silk of Nephila clavipes to their biochemical composition and physicochemical properties. Five layers of different make-ups could be distinguished. Of these only the two core layers contained the known silk proteins, but all can vitally contribute to the mechanical performance or properties of the silk fibre. Understanding the composite nature of silk and its supra-molecular organisation will open avenues in the production of high performance fibres based on artificially spun silk material.
Plant Cell, Tissue and Organ Culture, 1988
Physiologia Plantarum, 1990
... microbeam Gerd Weber, Shamci Monajembashi, Jiirgen Wolfrum and Kari-Otto Greulich ... With a ... more ... microbeam Gerd Weber, Shamci Monajembashi, Jiirgen Wolfrum and Kari-Otto Greulich ... With a focussed beam, cell wall components were removed (Hahne and Hoffman 1984) and pollen grains were per-forated (Sanford 1983). ...
Naturwissenschaften, 1988
Journal of Microscopy, 2000
Complete manipulation by laser light allows precise and gentle treatment of plant cells, subcellu... more Complete manipulation by laser light allows precise and gentle treatment of plant cells, subcellular structures, and even individual DNA molecules. Recently, affordable lasers have become available for the construction of microbeams as well as for optical tweezers. This may generate new interest in these tools for plant biologists. Early experiments, reviewed in this journal, showed that laser supported microinjection of material into plant cells or tissues circumvents mechanical problems encountered in microinjection by fragile glass capillaries. Plant protoplasts could be fused with each other when under microscopical observation, and it was no major problem to generate a triple or quadruple fusion product. In the present paper we review experiments where membrane material was prepared from root hair tips and microgravity was simulated in algae. As many plant cells are transparent, it is possible to work inside living, intact cells. New experiments show that it is possible to release by optical micromanipulation, with high spatial resolutions, intracellular calcium from caged compounds and to study calcium oscillations. An example for avian cardiac tissue is given, but the technique is also suitable for plant cell research. As a more technical tool, optical tweezers can be used to spatially fix subcellular structures otherwise moving inside a cell and thus make them available for investigation with a confocal microscope even when the time for image formation is extended (for example at low fluorescence emission). A molecular biological example is the handling of chromosomes and isolated individual DNA molecules by laser microtools. For example, chromosomes can be cut along complex trajectories, not only perpendicular to their long axis. Single DNA molecules are cut by the laser microbeam and, after coupling such a molecule to a polystrene microbead, are handled in complex geometries. Here, the individual DNA molecules are made visible with a conventional fluorescence microscope by fluorescent dyes such as SYBRGreen. The cutting of a single DNA molecule by molecules of the restriction endonuclease EcoRI can be observed directly, i.e. a type of single molecule restriction analysis is possible. Finally, mechanical properties of individual DNA molecules can be observed directly.
Journal of Microscopy, 2002
A Nd-YAG laser at 1064 nm is used as optical tweezers to move intracellular objects and a laser m... more A Nd-YAG laser at 1064 nm is used as optical tweezers to move intracellular objects and a laser microbeam to cause impairment of cytoskeleton tracks and influence intracellular motions in desmidiaceaen green algae. Naturally occurring migrations of large nuclei are inhibited in Micrasterias denticulata and Pleurenterium tumidum when the responsible microtubules are targeted with a laser microbeam generating 180 mW power in the focal plane. Impairment of the microtubule tracks appears to be irreversible, as the nucleus cannot pass the former irradiated area in Pleurenterium or remains abnormally dislocated in Micrasterias. The actin filament-dependent movement of secretory vesicles and smaller particles can be manipulated by the same IR-laser at 90 mW when functioning as optical tweezers. In Closterium lunula particles are displaced from their cytoplasmic tracks for up to 10 micro m but return to their tracks immediately after removing the light pressure gained by the optical tweezers. The cytoplasmic tracks consist of actin filament cables running parallel to the longitudinal axis of Closterium cells as depicted by Alexa phalloidin staining and confocal laser scanning microscopy. Dynamics and extensibility of the cytoplasmic strands connecting particles to the tracks are also demonstrated in the area of large vacuoles which are surrounded by actin filament bundles. In Micrasterias trapping of secretory vesicles by the optical tweezers causes irreversible malformations of the cell shape. The vesicle accumulation itself dissipates within 30 s after removing the optical tweezers, also indicating reversibility of the effects induced, in the case of actin filament-mediated processes.
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Papers by S. Monajembashi