The cellular composition of the colon epithelium is similar to that of the small intestine, but it contains a larger proportion of goblet cells interspersed among the columnar absorptive cells. In fact, the goblet cells of the colon are so large and abundant that the absorptive cells can be difficult to see. Goblet cells exhibit polarized morphology and a characteristic cup-like shape for which they are named. Nuclei and most organelles are located the base of goblet cells, while the rest of the cells are filled with secretory granules containing mucus.

In order to localize a red fluorescent tag to filamentous actin in the sample of rat colon tissue presented in the digital image above, the specimen was labeled with Alexa Fluor 568 conjugated to phalloidin, a phallotoxin commonly utilized in cell biology. Oregon Green 488 conjugated to the lectin wheat germ agglutinin, which selectively binds to N-acetylglucosamine and N-acetylneuraminic residues, was also applied to the tissue sample, as was the DNA probe Hoechst 33342. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.