Fig. 3

Ultrastructural features of differentiated enteroids mimic intact small intestinal tissue. a Canine jejunum enteroids, during early (day 3) and late (day 9) stages of differentiation, using whole tissue showing features of cellular differentiation, such as apical microvilli, electron-lucent cytoplasmic vacuoles (i.e., mucus), and electron-dense perinuclear granules (i.e., neurosecretory granules), consistent with development of absorptive enterocytes, goblet cells, and enteroendocrine cells, respectively. Ultrastructure features are visualized by representative transmission electron micrographs (TEM). b TEM of canine organoids show the progressive development (days 3–9 of differentiation) of intercellular structures important for intestinal barrier function. Adherens junction (AJ), tight junction (TJ), and desmosomes (D) structures are seen in both canine enteroids and native jejunum. On day 3, the developing tight junction had dilated paracellular space adjacent to tight junctions; however, the paracellular spaces were smaller on day 6, and no longer apparent by day 9. Representative images from at least n = 10 enteroids per condition