W C Sloos

Leiden University Medical Centre, Leiden, South Holland, Netherlands

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Publications (23)56.99 Total impact

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    ABSTRACT: Segregation of mitochondrial DNA (mtDNA) is an important underlying pathogenic factor in mtDNA mutation accumulation in mitochondrial diseases and aging, but the molecular mechanisms of mtDNA segregation are elusive. Lack of high-throughput single-cell mutation load assays lies at the root of the paucity of studies in which, at the single-cell level, mitotic mtDNA segregation patterns have been analyzed. Here we describe development of a novel fluorescence-based, non-gel PCR restriction fragment length polymorphism method for single-cell A3243G mtDNA mutation load measurement. Results correlated very well with a quantitative in situ Padlock/rolling circle amplification-based genotyping method. In view of the throughput and accuracy of both methods for single-cell A3243G mtDNA mutation load determination, we conclude that they are well suited for segregation analysis.
    Journal of Histochemistry and Cytochemistry 12/2007; 55(11):1159-66. · 2.26 Impact Factor
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    ABSTRACT: Apoptosis is fundamental to the regulation of homeostasis of stem cells in vivo. Whereas the pathways underlying the molecular and biochemical details of nuclear breakdown that accompanies apoptosis have been elucidated, the precise nature of nuclear reorganization that precedes the demolition phase is not fully understood. Here, we expressed an inducible caspase-8 in human mesenchymal stem cells, and quantitatively followed the early changes in nuclear organization during apoptosis. We found that caspase-8 induces alteration of the nuclear lamina and a subsequent spatial reorganization of both centromeres, which are shifted towards a peripheral localization, and telomeres, which form aggregates. This nuclear reorganization correlates with caspase-3 sensitivity of lamina proteins, because the expression of lamin mutant constructs with caspase-3 hypersensitivity resulted in a caspase-8-independent appearance of lamina intranuclear structures and telomere aggregates, whereas application of a caspase inhibitor restrains these changes in nuclear reorganization. Notably, upon activation of apoptosis, we observed no initial changes in the spatial organization of the promyelocytic leukemia nuclear bodies (PML-NBs). We suggest that during activation of the caspase-8 pathway changes in the lamina structure precede changes in heterochromatin spatial organization, and the subsequent breakdown of lamina and PML-NB.
    Journal of Cell Science 11/2006; 119(Pt 20):4247-56. · 5.88 Impact Factor
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    ABSTRACT: The underlying causes of mental retardation remain unknown in about half the cases. Recent array-CGH studies demonstrated cryptic imbalances in about 25% of patients previously thought to be chromosomally normal. Array-CGH with approximately 3500 large insert clones spaced at approximately 1 Mb intervals was used to investigate DNA copy number changes in 81 mentally impaired individuals. Imbalances never observed in control chromosomes were detected in 20 patients (25%): seven were de novo, nine were inherited, and four could not have their origin determined. Six other alterations detected by array were disregarded because they were shown by FISH either to hybridise to both homologues similarly in a presumptive deletion (one case) or to involve clones that hybridised to multiple sites (five cases). All de novo imbalances were assumed to be causally related to the abnormal phenotypes. Among the others, a causal relation between the rearrangements and an aberrant phenotype could be inferred in six cases, including two imbalances of the X chromosome, where the associated clinical features segregated as X linked recessive traits. In all, 13 of 81 patients (16%) were found to have chromosomal imbalances probably related to their clinical features. The clinical significance of the seven remaining imbalances remains unclear. The limited ability to differentiate between inherited copy number variations which cause abnormal phenotypes and rare variants unrelated to clinical alterations currently constitutes a limitation in the use of CGH-microarray for guiding genetic counselling.
    Journal of Medical Genetics 03/2006; 43(2):180-6. · 5.70 Impact Factor
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    ABSTRACT: The presence of tumor cells in bone marrow, peripheral blood and lymph nodes has proven its clinical and prognostic value. Since the frequency of these cells in bone marrow and blood is sometimes as low as 1 per million and due to the fact that for the analysis of lymph nodes many sectioning levels have to be analyzed, automated imaging devices have been suggested as an useful alternative to conventional manual screening of specimens. The aim of this paper is to review the performance of current equipment that is commercially available, based on literature published so far. Requirements for introducing this equipment for routine clinical practice are discussed.
    Cellular oncology: the official journal of the International Society for Cellular Oncology 02/2006; 28(4):141-50. · 4.17 Impact Factor
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    ABSTRACT: We report array-CGH screening of 95 syndromic patients with normal G-banded karyotypes and at least one of the following features: mental retardation, heart defects, deafness, obesity, craniofacial dysmorphisms or urogenital tract malformations. Chromosome imbalances not previously detected in normal controls were found in 30 patients (31%) and at least 16 of them (17%) seem to be causally related to the abnormal phenotypes. Eight of the causative imbalances had not been described previously and pointed to new chromosome regions and candidate genes for specific phenotypes, including a connective tissue disease locus on 2p16.3, another for obesity on 7q22.1-->q22.3, and a candidate gene for the 3q29 deletion syndrome manifestations. The other causative alterations had already been associated with well-defined phenotypes including Sotos syndrome, and the 1p36 and 22q11.21 microdeletion syndromes. However, the clinical features of these latter patients were either not typical or specific enough to allow diagnosis before detection of chromosome imbalances. For instance, three patients with overlapping deletions in 22q11.21 were ascertained through entirely different clinical features, i.e., heart defect, utero-vaginal aplasia, and mental retardation associated with psychotic disease. Our results demonstrate that ascertainment through whole-genome screening of syndromic patients by array-CGH leads not only to the description of new syndromes, but also to the recognition of a broader spectrum of features for already described syndromes. Furthermore, on the technical side, we have significantly reduced the amount of reagents used and costs involved in the array-CGH protocol, without evident reduction in efficiency, bringing the method more within reach of centers with limited budgets.
    Cytogenetic and Genome Research 02/2006; 115(3-4):254-61. · 1.84 Impact Factor
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    ABSTRACT: Balanced complex chromosome rearrangements (CCR) are extremely rare in humans. They are usually ascertained either by abnormal phenotype or reproductive failure in carriers. These abnormalities are attributed to disruption of genes at the breakpoints, position effect or cryptic imbalances in the genome. However, little is known about possible imbalances at the junction points. We report here a patient with a CCR involving three chromosomes (2;10;11) and eight breakpoints. The patient presented with behavioural problems as the sole phenotypic abnormality. The rearrangement, which is apparently balanced in G-banding and multicolour FISH, was shown by genomic array analysis to include a deletion of 0.15-1.5 Mb associated with one of the breakpoints. To explain the formation of this rearrangement through the smallest possible number of breakage-and-reunion events, one has to assume that the breaks have not occurred simultaneously, but in a temporal order within the span of a single cell division. We demonstrate that array comparative genomic hybridisation (CGH) is a useful complementary tool to cytogenetic analysis for detecting and mapping cryptic imbalances associated with chromosome rearrangement.
    Human Genetics 05/2005; 116(5):390-4. · 4.63 Impact Factor
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    ABSTRACT: Array-based comparative genomic hybridization allows high-resolution screening of copy number abnormalities in the genome, and becomes an increasingly important tool to detect deletions and duplications in tumor and post-natal cytogenetics. Here we illustrate that genomic arrays can also provide novel clues regarding the structural basis of chromosome rearrangement, including instability and mechanisms of formation of ring chromosomes. We also showed that array results might impact the recurrence risks for relatives of affected individuals. Our data indicate that chromosome rearrangements frequently involve more breaks than current cytogenetic models assume.
    American Journal of Medical Genetics Part A 02/2005; 132A(1):36-40. · 2.30 Impact Factor
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    ABSTRACT: To investigate the practicality and sensitivity of supervised automated microscopy (AM) for the detection of micrometastasis in sentinel lymph nodes (SLNs) from patients with breast carcinoma. In total, 440 SLN slides (immunohistochemically stained for cytokeratin) from 86 patients were obtained from two hospitals. Samples were selected on the basis of: (1) a pathology report mentioning micrometastases or isolated tumour cells (ITCs) and (2) reported as negative nodes (N0). From a test set of 29 slides (12 SLN positive patients, including positive and negative nodes), 18 slides were scored positive by supervised AM and 11 were negative. Routine examination revealed 17 positive slides and 12 negative. Subsequently, automated reanalysis of 187 slides (34 patients; institute I) and 216 slides (40 patients; institute II) from reported node negative (N0) patients showed that two and seven slides (from two and five patients, respectively) contained ITCs, respectively, all confirmed by the pathologists, corresponding to 5.9% and 12.5% missed patients. In four of the seven missed cases from institute II, AM also detected clusters of four to 30 cells, but all with a size < or = 0.2 mm. Supervised AM is a more sensitive method for detecting immunohistochemically stained micrometastasis and ITCs in SLNs than routine pathology. However, the clinical relevance of detecting cytokeratin positive cells in SLNs of patients with breast cancer is still an unresolved issue and is at the moment being validated in larger clinical trials.
    Journal of Clinical Pathology 09/2004; 57(9):960-4. · 2.44 Impact Factor
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    ABSTRACT: At present, reverse transcription (RT)-PCR against carcino-embryonic antigen mRNA is one of the few research tools for the detection of occult cells in histopathologically assessed negative lymph nodes from patients with colorectal cancer. The aim of this study was to investigate the suitability of supervised low-resolution image analysis of immunohistochemically stained sections as alternative. Multiple sections (n = 50) of regional lymph nodes from patients with colorectal cancer were immunohistochemically stained and analyzed by applying low-resolution image analysis (flatbed scanning) for semiautomated detection of cytokeratin (CK)-positive stained cells. The sensitivity of this approach was demonstrated for 20 patients with stage II colorectal cancer and compared with RT-PCR regarding the detection of clinically assessed recurrence of disease within 10 years. CK(+) cells were detected in all of the patients (n = 6; 100%) with recurrence, compared with five patients (83%) found positive by carcinoembryonic antigen RT-PCR. From patients (n = 14) who did not develop a recurrence, eight (57%) had positive lymph nodes. In all patients with recurrence, we visually identified at least one group of CK(+) cells (>/==" BORDER="0">2 cells). Automated image analysis is a promising tool for the detection of occult cells in histopathologically negative nodes. It is potentially more sensitive but less specific for detecting recurrence of disease than conventional histopathology or RT-PCR and is particularly useful for the evaluation of sentinel nodes. Furthermore, it opens new ways for basic research of occult cells based on molecular profiling after laser-microdissection.
    Clinical Cancer Research 10/2003; 9(13):4826-34. · 7.84 Impact Factor
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    ABSTRACT: At present, limiting factors in the use of tissue microarrays (TMAs) for high-throughput analysis relate to the visual evaluation of the staining patterns of each of the individual cores in the array and to the subsequent input of the results into a database. Such a database is essential to correlate the data with tumor type and outcome, and to evaluate the performance against other markers achieved in separate experiments. So far, these steps are mostly performed by hand, and consequently are time-consuming and potentially prone to bias and errors, respectively. This paper describes the use of a high-resolution flat-bed scanner for digitization of TMAs with a resolution of about 5 x 5 micro m(2). The arrays are acquired, the positions of the tissue cores are automatically determined, and measurement data including the images of the individual cores are archived. The program provides digital zooming of arrays for interactive verification of the results and rapid linkage of individual core images to data sets of other markers derived from the same array. Performance of the system was compared to manual classification for a representative set of arrays containing colorectal tumors stained with different markers.
    Journal of Molecular Diagnostics 09/2003; 5(3):160-7. · 3.95 Impact Factor
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    ABSTRACT: This article explores the feasibility of the use of automated microscopy and image analysis to detect the presence of rare fetal nucleated red blood cells (NRBCs) circulating in maternal blood. The rationales for enrichment and for automated image analysis for "rare-event" detection are reviewed. We also describe the application of automated image analysis to 42 maternal blood samples, using a protocol consisting of one-step enrichment followed by immunocytochemical staining for fetal hemoglobin (HbF) and FISH for X- and Y-chromosomal sequences. Automated image analysis consisted of multimode microscopy and subsequent visual evaluation of image memories containing the selected objects. The FISH results were compared with the results of conventional karyotyping of the chorionic villi. By use of manual screening, 43% of the slides were found to be positive (>=1 NRBC), with a mean number of 11 NRBCs (range 1-40). By automated microscopy, 52% were positive, with on average 17 NRBCs (range 1-111). There was a good correlation between both manual and automated screening, but the NRBC yield from automated image analysis was found to be superior to that from manual screening (P=.0443), particularly when the NRBC count was >15. Seven (64%) of 11 XY fetuses were correctly diagnosed by FISH analysis of automatically detected cells, and all discrepancies were restricted to the lower cell-count range. We believe that automated microscopy and image analysis reduce the screening workload, are more sensitive than manual evaluation, and can be used to detect rare HbF-containing NRBCs in maternal blood.
    The American Journal of Human Genetics 01/1999; 63(6):1783-92. · 11.20 Impact Factor
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    ABSTRACT: Fluorescence in situ hybridization allows the enumeration of chromosomal abnormalities in interphase cell nuclei. This process is called dot counting. To estimate the distribution of chromosomes per cell, a large number of cells have to be analyzed, especially when the frequency of aberrant cells is low. Automation of dot counting is required because manual counting is tedious, fatiguing, and time-consuming. We developed a completely automated fluorescence microscope system that can examine 500 cells in approximately 15 min to determine the number of labeled chromosomes (seen as dots) in each cell nucleus. This system works with two fluorescent dyes, one for the DNA hybridization dots and one for the cell nucleus. After the stage has moved to a new field, the image is automatically focused, acquired by a Photometrics KAF 1400 camera (Photometrics Ltd., Tuscon, AZ, USA), and then analyzed on a Macintosh Quadra 840AV (Apple Computer, Inc., Cupertino, CA, USA) computer. After the required number of cells has been analyzed, the user may interact to correct the computer by working with a gallery of the cell images. The automated dot counter has been tested on a number of normal specimens where 4,'6-diamidino-2-phenylindole (DAPI) was used for the nucleus counterstain and a centromeric 8 probe was used to mark the desired chromosome. The slides contained lymphocytes from cultured blood. We compared the results of the dot counter with manual counting. Manually obtained results, published in the literature, were used as the "ground truth." For a normal specimen, 97.5% of cells will have two dots. Fully automated scanning of 13 slides showed that an average of 89% of all nuclei were counted correctly. In other words, an average of 11% has to be interactively corrected, using a monitor display. The machine accuracies, after interactive correction, are comparable to panels of human experts (manual). The fully automatically obtained results are biased with respect to manual counting. An error analysis is given, and different causes are discussed.
    Cytometry 06/1997; 28(1):1-10.
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    ABSTRACT: We investigated the feasibility of automated counting of in situ hybridization signals (ISH) in interphase cells isolated from paraffin embedded prostate tissue. In total, 34 specimens from 7 patients with prostate cancer were stained with probes specific for the centromeric regions of chromosomes Y, 1, 7, 8, 10, and 15, using an immunoperoxidase based technique suitable for bright-field microscopy. Enumeration of the number of ISH spots of 500 nuclei per specimen was performed (1) using an automatic system developed without any human intervention and (2) using the same system, but including verification of the counts based on visual inspection of the stored images. As reference from each specimen, 200 cell nuclei were evaluated manually, using conventional microscopy. A typical analysis procedure (including user verification) took 35 min. The difference (root mean error) between the automated counting and the counting after visual interaction was relatively small (15%). The percentage of cells with incorrect counts by automated analysis was 20.2%, a number that could easily be improved by user interaction. Detection of cells with aneusomy proved to be more sensitive compared to the routine manual counting, in cases where aberrant frequencies were low. Automated counting of samples with low frequencies (< 10%) resulted in a higher frequency of aberrant cells in 9 of 11 cases, probably due to the fact that an unbiased cell selection is guaranteed. Automated assessment of ISH signals is considered useful for the evaluation of chromosomal aberrations in prostate tumor cells, provided that the counts are visually confirmed.
    Cytometry 12/1996; 26(4):298-304.
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    ABSTRACT: In situ hybridization techniques allow the enumeration of chromosomal abnormalities and form a great potential for many clinical applications. Although the use of fluorescent labels is preferable regarding sensitivity and colormultiplicity, chromogenic labels can provide an excellent alternative in relatively simple situations, e.g., where it is sufficient to use a centromere specific probe to detect abnormalities of one specific chromosome. When the frequency of chromosomal aberrations is low, several hundreds or even thousands of cells have to be evaluated to achieve sufficient statistical confidence. Since manual counting is tedious, fatiguing, and time consuming, automation can assist to process the slides more efficiently. Therefore, a system has been developed for automated spot counting using brightfield microscopy. This paper addresses both the hardware system aspects and the software image analysis algorithms for nuclei and spot detection. As a result of the automated slide analysis the system provides the frequency spot distribution of the selected cells. The automatic classification can, however, be overruled by human interaction, since each individual cell is stored in a gallery and can be relocated for visual inspection. With this system a thousand cells can be automatically analyzed in approximately 10 min, while an extra 5-10 min is necessary for visual evaluation. The performance of the system was analyzed using a model system for trisomy consisting of a mixture of male and female lymphocytes hybridized with probes for chromosomes 7 and Y. The sensitivity for trisomy detection in the seeding experiment was such that a frequency of 3% trisomic cells could be picked up automatically as being abnormal according to the multiple proportion test, while trisomy as low as 1.5% could be detected after interaction.
    Cytometry 07/1996; 24(2):158-66.
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    ABSTRACT: Fluorescence in situ hybridization allows the enumeration of chromosomal abnormalities in interphase cell nuclei. This process is called dot counting. To estimate the distribution of chromosomes per cell, a large number of cells have to be analysed, particularly when the frequency of aberrant cells is low. Automation of dot counting is desirable because manual counting is tedious, fatiguing, and time consuming. We have developed a completely automated fluorescence microscope system that counts fluorescent hybridization dots for one probe in interphase cell nuclei. This system works with two fluorescent dyes—one for the DNA hybridization dots and one for the cell nucleus. A fully automated scanning procedure has been used for the image acquisition. After an image is acquired it has to be analysed in order to find the nuclei and to detect the dots. This article focuses upon the dot detection procedure. Three different algorithms are presented. The problems of 'overlapping' dots and split dots are discussed. The automated dot counter has been tested on a number of normal specimens where DAPI was used for the nucleus counter stain and a centromeric probe was used to mark the chromosome 12. The slides contained lymphocytes from cultured blood. The performance of the different algorithms has been evaluated and compared with manually obtained results. The automated counting results approximate the results of manual counting.
    Bioimaging 06/1996;
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    ABSTRACT: With the advent of in situ hybridization techniques for the analysis of chromosome copy number or structure in interphase cells, the diagnostic and prognostic potential of cytogenetics has been augmented considerably. In theory, the strategies for detection of cytogenetically aberrant cells by in situ hybridization are simple and straightforward. In practice, however, they are fallible, because false classification of hybridization spot number or patterns occurs. When a decision has to be made on molecular cytogenetic normalcy or abnormalcy of a cell sample, the problem of false classification becomes particularly prominent if the fraction of aberrant cells is relatively small. In such mosaic situations, often > 200 cells have to be evaluated to reach a statistical sound figure. The manual enumeration of in situ hybridization spots in many cells in many patient samples is tedious. Assistance in the evaluation process by automation of microscope functions and image analysis techniques is, therefore, strongly indicated. Next to research and development of microscope hardware, camera technology, and image analysis, the optimization of the specimen for the (semi)automated microscopic analysis is essential, since factors such as cell density, thickness, and overlap have dramatic influences on the speed and complexity of the analysis process. Here we describe experiments that have led to a protocol for blood cell specimen that results in microscope preparations that are well suited for automated molecular cytogenetic analysis.
    Cytometry 06/1996; 24(2):151-7.
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    ABSTRACT: We have developed a completely automated fluorescence microscope system that can examine 500 cells in approximately 20 minutes to determine the number of labeled chromosomes (seen as dots) in each cell nucleus. This system works with two fluorescent dyes-one for the DNA hybridization dots (e.g. FITC) and one for the cell nucleus (e.g. DAPI). After the stage has moved to a new field the image is automatically focused, acquired by a Photometrics KAF 1400 camera, and then analyzed on a Macintosh Quadra 840AV computer. After the required number of cells has been analyzed, the user may interact to correct the computer by working with a gallery of the cell images. The machine accuracies are equal to panels of human experts (manual) and limited by the overlapping of dots in the 3D cell as seen through the 2D projection
    Pattern Recognition, 1994. Vol. 1 - Conference A: Computer Vision & Image Processing., Proceedings of the 12th IAPR International Conference on; 11/1994
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    ABSTRACT: Full automation on the scoring of radiation-induced chromosomal aberrations in conventionally stained metaphase spreads cannot be achieved reliably due to the complex image analysis problems involved. More success may be obtained by using in situ hybridization staining of the chromosomes. We describe the development of a system to detect metaphases on the basis of a fluorescent counterstain and subsequently analyze the number of translocations with the aid of whole chromosome paints fluorescing in a different colour. The system consists of a Macintosh IIfx computer, an automated Ergolux microscope equipped for fluorescence, and a Sony CCD camera. The performance of the metaphase finder was measured on a small set of slides counterstained with DAPI, whereas the suitability of the system for scoring aberrations was tested in a small feasibility study for the detection or radiation-induced translocations involving chromosome 4. The potentialities of the system for the use of multiple colours are discussed.
    International Journal of Radiation Biology 10/1994; 66(3):287-95. · 1.90 Impact Factor
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    ABSTRACT: A cell detection method based upon automated screening is described for recognition of low frequencies (1 in 100,000) of immuno-enzymatically labelled white blood cells in human peripheral blood. The used image cytometry instrumentation (LEYTAS) includes a wide-field, fully automated microscope (Autoplan) and a modular image analysis computer (MIAC), both from Leica, Wetzlar, Germany. The MIAC contains image boards for optimum use of mathematical morphology algorithms. Communication with the MIAC is via a personal computer. Programs for automated cell analysis have been written in C language. Main features of the system are fast analysis of large microscope fields including a count of all cells, selection of objects of interest (alarms), and display of digitally stored images of these alarms. We tested this system for the detection of white blood cells expressing antigen of cytomegalovirus (pp65) in 50 human blood smears from kidney transplant recipients. Immuno-enzymatic (peroxidase) staining was performed with DAB and counterstaining with hematoxylin. For determination of the sensitivity, a series of dilutions of a positive sample with a negative sample was performed. The lowest frequency detected was 1 antigen-positive cell/3 x 10(5) antigen-negative cells. Screening time was about 60 min for one million cells.
    Cytometry 04/1994; 15(3):199-206.
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    ABSTRACT: Cooled CCD cameras provide good sensitivity and linearity with a high dynamic range and are therefore well suited for quantification of fluorescence in situ hybridization signals. However, for a fraction of the cost, conventional noncooled, video-rated CCD cameras can also be applied for most applications in the field of fluorescence in situ hybridization, provided that they allow for longer integration times. This paper describes the use of the Sony camera, model XC-77RR-CE, for this purpose. Tests were carried out to compare the dark current, linearity, and signal-to-noise ratio of this camera with a Photometrics cooled CCD camera model KAF 1400, and the suitability for quantitative measurements was investigated on a model system of fluorescent beads. It is shown that if the dark current of the video-rated camera is internally corrected, integration times of up to 30 s can be used; under such conditions good linearity is maintained. The camera was found suitable for the detection of in situ hybridization spots in interphase nuclei using centromere-specific probes. The fast readout rate of the camera offers interesting facilities for quickly locating objects with relatively strong fluorescence, such as counterstained metaphases. The less intense probe signals may then be analyzed at higher magnification.
    Cytometry 02/1994; 15(1):2-11.

Publication Stats

520 Citations
56.99 Total Impact Points

Institutions

  • 1999–2005
    • Leiden University Medical Centre
      • Department of Molecular Cell Biology
      Leiden, South Holland, Netherlands
  • 1994–1997
    • Delft University of Technology
      Delft, South Holland, Netherlands
  • 1994–1996
    • Leiden University
      • Molecular Cell Biology Group
      Leyden, South Holland, Netherlands