Here we describe a protocol for the automated segmentation of fluorescently labeled tissues on slides using a widefield high-content analysis system (WHCAS). This protocol has wide-ranging applications in any field which involves the quantitation of fluorescent markers in biological tissues including the biological sciences, medical engineering, and health sciences.
Automated slide scanning and segmentation of fluorescently-labeled tissues is the most efficient way to analyze whole slides or large tissue sections. Unfortunately, many researchers spend large amounts of time and resources developing and optimizing workflows that are only relevant to their own experiments. In this article, we describe a protocol that can be used by those with access to a widefield high-content analysis system (WHCAS) to image any slide-mounted tissue, with options for customization within pre-built modules found in the associated software. Not originally intended for slide scanning, the steps detailed in this article make it possible to acquire slide scanning images in the WHCAS which can be imported into the associated software. In this example, the automated segmentation of brain tumor slides is demonstrated, but the automated segmentation of any fluorescently-labeled nuclear or cytoplasmic marker is possible. Furthermore, there are a variety of other quantitative software modules including assays for protein localization/translocation, cellular proliferation/viability/apoptosis, and angiogenesis that can be run. This technique will save researchers time and effort and create an automated protocol for slide analysis.
The accurate and precise quantitation of fluorescently-labeled tissues on slides is a highly sought-after technique in many scientific fields. However, researchers often manually count specimens or spend considerable amounts of time developing esoteric automated techniques to achieve this. Herein, we provide a protocol for the automated slide scanning and quantitation of cells using a WHCAS and its associated software, with innate immune cells in frozen human brain tumor sections as an example. The associated software offers a wide range of built-in customizable modules from neurite outgrowth counting to differentiation of cell types1,2,3,4,5,6. The goal of this method is to provide researchers with a start-to-finish, easily reproducible protocol to acquire images of and quantitate fluorescently-labeled entities in any slide-mounted tissues.
In this protocol, the WHCAS is mainly used for imaging plates for the subsequent analysis on the associated software even though a slide adapter and the basics to slide scanning7 were available. It was prohibitive to image slides because the careful spatial calibration of the acquisition area, the selection of appropriate journals, the creation of tailored loadouts, and a liaison with product representatives were required. In the wider body of literature, in lieu of purchasing a dedicated slide-imaging and analysis apparatus8, a previous technological report with access to this software circumvented the image acquisition of slides on the WHCAS altogether9. Performing image acquisition or image analysis on different platforms necessitates extra work to ensure each is compatible with the other.
The ability to use the WHCAS and its software for image capture would avoid the unnecessary complications of searching for or developing a workflow alien to these tools. In this article, the steps required to create a low magnification overview scan and the corresponding high magnification images by treating the slide as a plate, and the subsequent analyses using the Multi-Wavelength Cell Scoring segmentation module allow for the repurposing of the WHCAS. This readily usable protocol provides an advantage over alternative techniques because there is no need to develop algorithms or multi-step counting protocols10,11 once the images are acquired on the WHCAS. This protocol mitigates the time required to optimize a quantitation technique, is more precise12 and efficient than manual counting and maximizes the use of the WHCAS. This protocol can be widely and easily used since it enables the imaging and analysis of any fluorescently-labeled tissues on slides.
Tumor specimens were obtained as per the protocol approved by the local institutional review board and ethics committee and conducted in accordance with national regulations. The WHCAS and its associated software used in this article are listed in the Table of Materials.
1. Importing the Journals
2. Creating Settings for Preview Scan Acquisition
3. Creating Settings for Slide Acquisition at High Magnification
4. Placing the Slide in the Widefield High-content Analysis System
5. Acquiring a Preview Scan
6. High Magnification Scanning
7. Image Analysis
The images can be viewed within the WHCAS software. Figure 8 shows the high magnification thumbnails of all sites within the defined region of interest. Review each site to identify the ones that should be excluded from the analysis (examples are shown at low and high magnification in Figure 8 and Figure 9, respectively). For example, Site 149 is out of focus (Figure 9A), Site 219 has bubbles (Figure 9B), and Site 54 contains a fold (Figure 9C) and should be excluded. It is typical to exclude 10 – 15% of all sites imaged. In the example provided, 15.3% of the sites were excluded (25/300 had bubbles, 17/300 were out of focus, 3/300 were folded, and 1/300 was on the edge). Figure 10A is a representative image chosen for analysis (its corresponding low magnification thumbnail is shown in Figure 8). Here, the corresponding overlays generated by the Multi-Wavelength Cell Scoring module demonstrate the results of the automated segmentation performed on Site 59, customized to the authors' specifications (nuclei minimum width = 2.5 µm, maximum width = 7.5 µm, and intensity above local background = 35 graylevels; CD11b-positive cells' minimum width = 4 µm, maximum width = 18 µm, minimum stained area = 15 µm2, and intensity above local background = 310 graylevels; and CD45-positive cells' minimum width = 4 µm, maximum width = 18 µm, minimum stained area = 15 µm2, and intensity above local background = 50 graylevels). Following the segmentation, the quantitative data of the proportion of cells staining positive for each marker (6.2 ± 5.1% and 3.8 ± 2.1% of CD11b+ and CD45+ cells, respectively), both markers (3.5 ± 2.1% CD11b+CD45+ cells), no markers (86.6 ± 9.0% CD11b–CD45– cells; Figure 10B), mean stained area (40.0 ± 9.2 µm and 36.7 ± 7.6 µm of CD11b+ and CD45+ cells, respectively; Figure 10C), and mean fluorescence intensity (408.9 ± 40.3 relative fluorescence units and 373.9 ± 38.1 relative fluorescence units of CD11b+ and CD45+ cells, respectively; Figure 10D) can be obtained.
Figure 1: Settings for slide acquisition at low magnification. A. This image displays the plate settings. B. Here, the plate bottom settings are displayed. Please click here to view a larger version of this figure.
Figure 2: Settings for slide acquisition at high magnification. This figure displays the selection of the appropriate journals. Please click here to view a larger version of this figure.
Figure 3: Demonstration of how to load slides using the slide adapter. A. The slide is placed coverslip down with the label on the side of the slide adapter notch. B. The slide adapter is loaded into the widefield high-content analysis system. Please click here to view a larger version of this figure.
Figure 4: Preview slide settings. A. This figure displays the parameters for the acquisition. B. Here, the values for the Hoescht/DAPI wavelength settings are displayed. C. This image shows the journal settings. Please click here to view a larger version of this figure.
Figure 5: Drawing a slide region. A. The rectangular region tool (other drawing tools cannot be used) is used to select the preview scan area and create regions of interest on the DAPI scan. B. The teal outline in this figure shows how the entire area of the slide (including the label) should be selected. Please click here to view a larger version of this figure.
Figure 6: Creating regions of interest on the preview scan. The preview or DAPI scan represents the entire slide area. In this example, there are three serial brain tissue sections (the solid white rectangular outlines). The area above these sections represents the circular labels on the slide. Different section arrangements will not limit the subsequent selection of regions of interest. The region of interest in this particular example is shown with a dashed white rectangular outline. The scalebar = 1 mm. Please click here to view a larger version of this figure.
Figure 7: Essential windows for high magnification image acquisition. A. The Acquisition Site Setup window will show how many columns and rows are within the region(s) of interest. B. Ensure the correct number of columns and rows indicated in Figure 7A are entered into the Plate Acquisition Setup box and the sites are tiled. C. It is necessary to keep the WellPositions window open for the duration of the image acquisition even though it is blank. D. The appropriate number of regions of interest must be highlighted. Please click here to view a larger version of this figure.
Figure 8: Representative image of the region of interest. Each site can be displayed in a composite thumbnail of the region of interest. The representative sites that have been excluded (marked with red boxes) and an example of an included site (marked with a green box) is shown at a higher magnification. It is recommended to review each site to ensure it is of sufficient quality for the analysis. The scalebar = 1 mm. Please click here to view a larger version of this figure.
Figure 9: Examples of sites that should be excluded from analysis. A. The human brain tumor sections have been stained with CD11b (green) and CD45 (red), markers of microglia and macrophages. This image is out of focus and has been excluded from the analysis. B. Bubbles are present in this image which has been excluded from the final analysis. C.This site was excluded from the analysis because of the fold in the tissue. The scale bars are 20 µm. Please click here to view a larger version of this figure.
Figure 10: Representative images and analysis. A. Each image is displayed next to the overlays representing the results of the automated segmentation. In the overlay, nuclei are displayed in white and positively stained cells are shown in green for CD11b and red for CD45. After excluding the sites of inadequate quality from the analysis and combining the results of all the remaining sites, B. the average proportions of the total number of cells in each site that stained positive for each marker and co-labeled for both markers, C. the average stained area, and D. the average cell intensity are graphically represented. RFU = relative fluorescence units. The data are expressed as mean ± standard deviation. The scale bars are 20 µm. Please click here to view a larger version of this figure.
A common problem still impeding the efficiency of biological science research is the development of protocols for the unbiased, accurate, and precise quantification of fluorescently-labeled tissues and their structures within. Significant amounts of time and effort are directed towards finding ways to analyze tissue slides once they have been imaged. Many existing methods provide algorithms for users to recreate within programs12,13,14. These methods are acceptable, but the significance of this report is that it enables the user to easily and quickly establish a holistic image acquisition and analysis protocol if the user has access to a WHCAS. Assays that differentiate cell types and quantify multiple structures and processes, cell cycle analysis, and nuclear translocation, for example, are already available in the associated software.
The setup involves a few critical steps. Firstly, the spatial parameters of the slide are defined as if it were a plate. Secondly, a low magnification overview scan is created from which regions of interest are selected for high magnification imaging. Lastly, sites that affect the accuracy and precision of subsequent analyses are excluded. The biggest limitation of this technique is that its applicability depends on if the user has access to a WHCAS. However, with the increasing need for high-content analysis systems, many institutions are providing these to their researchers to remain competitive15. Troubleshooting is needed most commonly when tissue sections do not have the same thickness. If multiple regions of interest are selected, some will be in focus while others will not. Ideally, during sectioning, the user would take care to create homogeneous samples. However, if the samples are inconsistent, the focus on the nuclear stain wavelength (or the user's brightest fluorophore), which is used to focus, can be readjusted for each out-of-focus region of interest and even for each field of view. As the other wavelengths are simply offset from the nuclear stain wavelength, only this wavelength needs readjustment.
In this report, we detail how to scan and analyze slides using a WHCAS and associated software. The Multi-Wavelength Cell Scoring module allows the user to automatically count any nuclear or cytoplasmic markers that are fluorescently labeled. After adjusting the focus settings and defining the cellular characteristics such as width and area to customize the module to the tissue imaged, there is no further need for user intervention to obtain the imaged slides and quantitative data. Up to three slides can be imaged at a time and multiple regions of interest can be defined. This protocol lets WHCAS users who need to analyze slides take advantage of customizable, multipurpose, automated workflows that require little to no optimization and can be applied in any projects in the future that involve the histological analysis of tissue.
The authors have nothing to disclose.
This project was funded by a grant from the Canadian Institutes of Health Research and Alberta Innovates – Health Solutions/Alberta Cancer Foundation. The authors wish to acknowledge the Regeneration Unit in Neurobiology core facility for the use of their equipment, the work of Paula Gedraitis in building the foundation upon which slide scanning on the WHCAS was made possible, and the creator of the products mentioned in this article, Molecular Devices.
ImageXpress MicroXLS | Molecular Devices | NA | Apparatus for image acquisition |
MetaXpress 5.1 | Molecular Devices | NA | Associated software for ImageXpress MicroXL (runs on a PC with the Windows operating system). |
Slide adapter | Molecular Devices | NA | Metal slide holder that fits into ImageXpress MicroXL |
Slide_Region_Acquisition_revA.jzp | Molecular Devices | NA | The journal can be obtained from metamorph.moleculardevices.com/forum/showthread.php?tid=218&highlight=slide or from contacting a Molecular Devices representative |
Slide_Region_Acquisition_Setup.JNL | Molecular Devices | NA | Select this journal in Step 6.6. |