Journal: Frontiers in Endocrinology
Article Title: CU Cilia – an application for image analysis by machine learning – reveals significance of cysteine cathepsin K activity for primary cilia of human thyroid epithelial cells
doi: 10.3389/fendo.2025.1588394
Figure Lengend Snippet: Cysteine peptidase activity at primary cilia of human thyroid epithelial cells in vitro . Confocal fluorescence micrographs of cultured human thyroid epithelial cells upon incubation with the cysteine peptidase-specific activity-based probe DCG-04 for 1 h ( A , green), fixation with paraformaldehyde and methanol, and immunostaining with antibodies against the cilia marker ARL13B ( A , red; B-D , green). Non-treated controls were immuno-stained with antibodies specific for ARL13B ( B-D , green) and cathepsin B ( B , red), cathepsin K ( C , red) or cathepsin L ( D , red). Counter-staining of nuclear DNA was with Draq5™ (a1, a5, b1, b5, c1, c5, d1, d5, blue; N, nuclei). For better contrast, the single fluorescence channels are displayed as grey scale images with inverted colors, while merged channel images are displayed as indicated. Arrowheads denote vesicular cathepsin staining in the peri-nuclear regions, whereas circles indicate immuno-recognized puncta in the extracellular space. Boxed areas in a1-a4, b1-b4, c1-c4, and d1-d4 are shown in higher magnification in a5-a8, b5-b8, c5-c8, and d5-d8, respectively. Note that some primary cilia of human thyroid epithelial cells in vitro are positive for cysteine peptidase activity (cyan boxed cilia in A ), while others lacked proteolytic activity (red boxed cilia in A ). Cathepsins B and L are abundantly detected in endo-lysosomal vesicles ( B, D , arrowheads) that are typically located around the base of primary cilia which originate from the centrosomes of the microtubule-organizing centers in juxta-nuclear position. Cathepsin K is more abundant throughout the cytoplasm and present in the extracellular space ( C , circles). Scale bars represent 20 µm in a1-a4, b1-b4, c1-c4 and d1-d4, while 5 µm are indicated in a5-a8, b5-b8, c5-c8, and d5-d8, respectively.
Article Snippet: For primary cilia detection, rabbit anti-human/mouse/rat/dog ARL13B (#17711-1-AP, 1:250, Proteintech, Planegg, Germany, RRID: AB_2060867) was used, followed by secondary antibody incubation, namely, goat anti-rabbit Alexa Fluor 546 or Alexa Fluor plus 488 F(ab’) fragments (1:200, Thermo Fisher Scientific, Bremen, Germany, #A11071, RRID: AB_2534115, and #A48282TR, RRID: AB_2896346, respectively) were used.
Techniques: Activity Assay, In Vitro, Fluorescence, Cell Culture, Incubation, Immunostaining, Marker, Staining