Figure 1.

AXL Expression Is a Feature of Rare Adult Human Breast Epithelial Cells

AXL is expressed in rare epithelial cells in normal breast epithelium.

(A–D) (A) Multi-color immunofluorescence analysis of normal breast epithelium biopsies (n = 20). The ducts shown in (A–D) are formalin-fixed paraffin-embedded (FFPE) tissue sections stained with monoclonal antibodies against AXL (MAB10C9, white), MEP-specific cytokeratin 14 (K14, red), and luminal epithelial-specific cytokeratin 19 (K19, green); nuclear counterstain (DAPI, blue).

(E-H) Cryosections of normal human breast epithelium stained with monoclonal antibodies against: (E) AXL (ab21965, green), (F) K19 (magenta), (G) K14 (red). Overlay (H) reveals the areas of co-localized expression of AXL, K19, and K14 (white) in the lobular acini.

(I) Chromogenic IHC of AXL (ab21965, HRP-DAB brown) on FFPE sections of human mammary tissue. Counterstain by hematoxylin (blue).

(J–M) RNA in situ hybridization (RNA-ISH) on FFPE breast tissue specimens reveal the localization and distribution of (J) AXL mRNA transcripts, and (K) mRNA transcripts of the AXL-ligand GAS6. Each dot (brown, HRP-DAB) represents a single RNA molecule. (L and M) Histo-score analysis was performed to quantify the heterogeneity of the AXL and GAS6 mRNA transcripts within the breast epithelium at the single cell level. The Histo-score of transcript expression was determined by categorizing epithelial cells in five predefined bins based on the number of transcripts per cell. Distribution (% of cells/bin) as well as Histo-scores provided on a range of 0-400 is given.

(N) Dual RNA ISH on paraffin-embedded section of normal human breast specimen reveal the spatial distribution and juxtaposition of AXL (AP-based Fast Red) and GAS6 (HRP-based Green) mRNA transcripts within the normal human mammary epithelium. Counterstain by hematoxylin (blue).

The ducts shown in (A–D), (I), and (M–K), and (N), and the lobular acini shown in (E–H) are obtained from tumor biopsies from different patients.