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    A computational pipeline to quantify primary cilia in mouse embryonic fibroblasts with CellProfiler

    Suzanne R Pfeffer, Herschel Dhekne, Ebsy Jaimon, Chloe A Hecht, Sreeja V Nair

    Published: 2023-09-08 DOI: 10.17504/protocols.io.bp2l6x2j5lqe/v1
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    Abstract

    We present here an automated CellProfiler (Stirling et al., 2021) software pipeline to quantify the number of primary cilia in cultured cells. The primary cilia were labeled using anti-Arl13b antibodies and nuclei were labeled using DAPI. This protocol works with .czi format images which are acquired using a Zeiss laser scanning confocal microscope and are maximum intensity projected.

    Steps

    Import data into CellProfiler and extract metadata from file names

    1.

    Select the  Images  module, drag and drop the maximum intensity projected .TIF files as indicated

    2.

    Select the Metadata  module

    In the Metadata module: 

    Extract metadata? Yes.

    Metadata extraction method: Extract from file/folder names

    Metadata source: File name

     Regular expression to extract file name : 

     “regular expression” will have the form: 

    ^(?P[A-Z)]{2}).*#(?P[0-9]{2}) to extract the cell type and image number from an example file name "WTcells - WTcells #14_max.tif."

     Here,

    ^ indicates the beginning of the file name

    (?P[A-Z]{2}) tells the program to name the captured field “celltype” and recognize two letters that follow

    (?P[0-9]{2}) tells the program to name the captured field “imagenumber” and recognize two digits that follow

     

    Extract metadata from: All images

     

    Add another extraction method

    Metadata extraction method: Extract from image file headers       

    Extract metadata from: All images

    Hit “Extract metadata”

    Metadata data type: Text

    Hit “update” to populate the metadata field

    Group individual channels and create image subsets

    3.

    Go to  Names and types module 

    Assign a name to : “Images matching rules” 

    Process as 3D : No

    Select the rule criteria

    Match “All” of the following rules 

    “Metadata/Does/Have C matching 0”

    Name to assign these images: Arl13b

    Select the image type: Grayscale image

    Set intensity range from : Image metadata

     

    Add another image

     

    Match “All” of the following rules 

    “Metadata/Does/Have C matching 1”

    Name to assign these images: dapi

    Select the image type: Grayscale image

    Set intensity range from : Image metadata

     

    Hit “update” to populate the names and types field

    4.

    Select  Groups module

     

    Do you want to group your images? Yes

    Metadata category: celltype

    Add another metadata item

    Metadata category: imagenumber

     

    This groups images based on cell type and image number as identified in the metadata module.

    Identification of nuclei

    5.

    Click on the “+” sign at the bottom next to Adjust Modules. One can choose different modules by double-clicking from the list or by typing in the search box. Under module category, object processing, add  Identifyprimaryobjects module.

     

    Use advanced settings? Yes

    Select the input image: dapi

    Name the primary objects to be identified: nuclei

    Typical diameter of objects, in pixel units: 60-200

    Note :

    This has to be optimized for each image set.

     

    Discard objects outside the diameter range? Yes

    Discard objects touching the border of the image? No

     

    Note:

    Check by clicking “Start Test Mode” and hitting the green triangle next to the IdentifyPrimaryObjects module. 

     

    Threshold strategy? Global

    Thresholding method? Minimum Cross-Entropy

    Threshold smoothing scale 1.3488 

    Threshold correction factor 1.0

    Lower and upper bounds on threshold 0.05 and 0.8

    Log transform before thresholding? No

    Method to distinguish clumped objects? Intensity

    Method to draw dividing lines between clumped objects? Intensity

    Automatically calculate size of smoothing filter for declumping? No

    Size of smoothing filter 30

    Automatically calculate minimum allowed distance between local maxima? Yes

     Speed up by using lower-resolution image to find local maxima? Yes

    Display accepted local maxima? No

    Fill holes in identified objects? After both thresholding and declumping 

    Handling of objects if excessive number of objects identified? Continue

     

    Note

     

    These parameters will need to be optimized for each image set. Check by clicking “Start Test Mode” and hitting the green triangle next to the IdentifyPrimaryObjects module each time a parameter is changed to find the best parameters for each image set. Green outlines represent valid objects whereas magenta/orange outlines represent invalid objects, as they are either touching the border or outside the diameter range set.

    Figure 1:  Nuclei in the input image(left) and nuclei identified as objects by CellProfiler (right). Green outlines represent valid objects.
    Figure 1: Nuclei in the input image(left) and nuclei identified as objects by CellProfiler (right). Green outlines represent valid objects.

    Identification of primary cilia objects

    6.

    Add  Identifyprimaryobjects module

    Use advanced settings? Yes

    Select the input image: Arl13b

    Name the primary objects to be identified: cilia

    Typical diameter of objects, in pixel units: 5-15

    Discard objects outside the diameter range? Yes

    Discard objects touching the border of the image? Yes

    Threshold strategy? Global

    Thresholding method? Otsu

    Two-class or three-class thresholding? Two classes

    Threshold smoothing scale 1.0

    Threshold correction factor 0.5

    Lower and upper bounds on threshold 0.0 and 1.0

    Log transform before thresholding? No

    Method to distinguish clumped objects? None

    Fill holes in identified objects? After both thresholding and declumping 

    Handling of objects if excessive number of objects identified? Continue

     

    Note

    Check by clicking “Start Test Mode” and hitting the green triangle next to the IdentifyPrimaryObjects module each time a parameter is changed to find the best parameters for each image set.

    Figure 2: Primary cilia in the input image (left) and cilia identified as objects by CellProfiler (right). Green outlines represent valid objects.
    Figure 2: Primary cilia in the input image (left) and cilia identified as objects by CellProfiler (right). Green outlines represent valid objects.

    Measuring the number of cilia and nuclei in each image

    7.

    Add  MeasureObjectSizeShape  module 

    Select object sets to measure : cilia, nuclei

    Calculate Zernike features?No

    Calculate the advanced features? No

    Exporting data

    8.

    Add the ExportToSpreadsheet module from the + at the bottom

    Select the column delimiter: Tab

    Output file : choose a folder where you want the images to be saved.

    Add a prefix to file names? Yes. 

    File name prefix: Add experiment identifier

    Overwrite existing files without warning? No

    Note: While the pipeline is run for optimizing the parameters, choose Yes to avoid being asked to rewrite each file.

    Add image metadata columns to your object data file? Yes

    Add image file and folder names to your object data file? No

    Representation of Nan/Inf: NaN

    Select measurements to export? Yes

    Press button to select measurements: 

    Select measurements: Choose number under cilia and nuclei

    Calculate the per-image mean values for object measurements? No

    Calculate the per-image median values for object measurements? No

    Calculate the per-image standard deviation values for object measurements? No

    Create GenePattern GCT file? No

    Export all measurement types? No

    Data to export: nuclei

    Use the object name for the file name? Yes

    Add another data set

    Data to export: cilia

    Combine these object measurements with those of the previous object? Yes

     

    Save the pipeline from File-Save Project and hit  Analyze Images on bottom left.

    The pipeline will run and export the data to the folder previously specified. The output file can be opened in Excel software. Distinct columns will indicate number of nuclei and number of cilia in each image.  

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