Markers to identify proliferating cell populations. Identification of intestinal stem and transit amplifying cells in equine enteroids are shown. Immunostaining for SOX9 (red, panel A and C), a transcription factor that is primarily expressed in active intestinal stem cells and transit-amplifying progenitor cells is localised to the nuclei of cells along the primitive enteroid buds. Colocalisation with a general marker of proliferation (Ki67+, green, panel B and C) is also seen. Digital magnification demonstrating colocalisation (yellow) of SOX9 (red) and Ki67 (green) is provided. Nuclei, blue (panel D). Insert scale bar 20 μm.