Optimization of Fast-FISH for alpha-satellite DNA probes

Single Molecule Localization Microscopy for Studying Small Extracellular Vesicles

Small extracellular vesicles (sEVs) are 30-200 nm nanovesicles enriched with unique cargoes of nucleic acids, lipids, and proteins. sEVs are released by all cell types and have emerged as a critical mediator of cell-to-cell communication. Although many studies have dealt with the role of sEVs in health and disease, the exact mechanism of sEVs biogenesis and uptake remain unexplored due to the lack of suitable imaging technologies. For sEVs functional studies, imaging has long relied on conventional fluorescence microscopy that has only 200-300 nm resolution, thereby generating blurred images. To break this resolution limit, recent developments in super-resolution microscopy techniques, specifically single-molecule localization microscopy (SMLM), expanded the understanding of subcellular details at the few nanometer level. SMLM success relies on the use of appropriate fluorophores with excellent blinking properties. In this review, the basic principle of SMLM is highlighted and the state of the art of SMLM use in sEV biology is summarized. Next, how SMLM techniques implemented for cell imaging can be translated to sEV imaging is discussed by applying different labeling strategies to study sEV biogenesis and their biomolecular interaction with the distant recipient cells.

Automated microaxial tomography of cell nuclei after specific labelling by fluorescence in situ hybridisation

Microaxial tomography provides a good means for microscopic image acquisition of cells or sub-cellular components like cell nuclei with an improved resolution, because shortcomings of spatial resolution anisotropy in optical microscopy can be overcome. Thus, spatial information of the object can be obtained without the necessity of confocal imaging. Since the very early developments of microaxial tomography, a considerable drawback of this method was a complicated image acquisition and processing procedure that requires much operator time. In order to solve this problem the Heidelberg 2pi-tilting device has been mounted on the Brno high-resolution cytometer as an attempt to bring together advanced microscopy and fast automated computer image acquisition and analysis. A special software module that drives all hardware components required for automated microaxial tomography and performs image acquisition and processing has been developed. First, a general image acquisition strategy is presented. Then the procedure for automation of axial tomography and the developed software module are described. The rotation precision has been experimentally proved followed by experiments with a specific biological example. For this application, also a method for the preparation of cell nuclei attached to glass fibres has been developed that allows for the first time imaging of three-dimensionally conserved, fluorescence in situ hybridisation-stained cell nuclei fixed to a glass fibre.

Quantitative microscopy after fluorescence in situ hybridization - a comparison between repeat-depleted and non-depleted DNA probes

Complex probes used in fluorescence in situ hybridization (FISH) usually contain repetitive DNA sequences. For chromosome painting, in situ suppression of these repetitive DNA sequences has been well established. Standard painting protocols require large amounts of an unlabeled 'blocking agent', for instance Cot-1 DNA. Recently, it has become possible to remove repetitive DNA sequences from library probes by means of magnetic purification and affinity PCR. Such a 'repeat depleted library probe' was hybridized to the q-arm of chromosome 15 of human metaphase spreads and interphase cell nuclei without any preannealing by Cot-1 DNA. Apart from this, 'standard' FISH conditions were used. After in situ hybridization, microscope images were obtained comparable to those achieved with the #15q library probe prior to depletion. The images were recorded by a true color CCD camera. By digital image analysis using 'line scan' and 'area scan' procedures, the painting efficiency expressed in terms of relative fluorescence signal intensity was quantitatively evaluated. The painting efficiency using the repeat depleted probe of chromosome 15q was compared to the painting efficiency after standard FISH. The results indicate that both types of probes are compatible to a high FISH efficiency. Using equivalent probe concentrations, no significant differences were found for FISH with standard painting probes and repeat depleted painting probes.

Comparison of the thermal denaturation behaviour of DNA-solutions and metaphase chromosome preparations in suspension

Hyperchromicity measurements are well established to analyse the thermal denaturation behaviour of pure DNA sequences in solution. Here, we show that under appropriate experimental conditions this technique can also be applied to study thermally controlled conformation changes of higher order DNA-protein complexes as for instance metaphase chromosome preparations in suspension. A computer controlled sensitive, upright double beam photometer with a heatable cuvette was constructed. Measurements of the temperature dependent extinction of both, solutions and particle suspensions are possible, since sedimentation effects of particles can be neglected due to the vertical optical axis in the probe cuvette. Thermal denaturation of metaphase chromosome preparations of human and Chinese hamster cells was investigated and compared to melting profiles of DNA solutions for two excitation wavelengths, 256 and 313 nm. The influence of neutral and low pH was considered. The results indicate that metaphase chromosome preparations show a thermal denaturation behaviour different from pure DNA. Whereas DNA solutions showed one pH dependent melting peak at 256 nm only, the peak pattern of metaphase chromosome preparations showed a large variability both at 256 and 313 nm. At neutral pH, in two temperature regions (40-55 degrees C and 75-82 degrees C) peaks were found indicating chromosome typical conformation changes independently from the mammalian cell species (Chinese hamster, human). In contrast to pure DNA, no typical reduction in the temperatures of peak maxima with decreasing pH was found for metaphase chromosome preparations of both cell types. These results may be relevant for further systematic studies of efficient thermal probe/target denaturation procedures in non enzymatic DNA-chromosome in situ hybridisation.

Fast-in situ hybridization and immunoenzymatic color pigment detection of mouse bone marrow micronucleus

The development of a whole mouse genomic DNA probe coupled to color pigment painting detection methodology can accurately verify mouse micronuclei induced by chemicals or drugs leading to a lower probability of potential artifacts. Using color pigment painting detection of probes in conjunction with Wright's Giemsa counterstain instead of the current fluorescence detection technology ensures low cost, high resolution permanent documentation of slides for a particular test compound. The permanent color pigment-detected micronuclei and adjoining counterstain allows slides to be stored for future analysis without enhancing the signal or adding antifading agents that are associated with fluorescence detection. Combining innovative technology such as fast-in situ hybridization of DNA probes with immunoenzymatic color pigment detection provides rapid verification of true micronuclei (DNA containing) within 2-3 hr.