Data from: Phagocytic intracellular digestion in amphioxus (Branchiostoma)

The digestive methods employed by amphioxus (Branchiostoma)—both
intracellular phagocytic digestion and extracellular digestion—have been
discussed since 1937. Recent studies also show that epithelial cells
lining the Branchiostoma digestive tract can express many immune genes.
Here, in Branchiostoma belcheri, using a special tissue fixation method,
we show that some epithelial cells, especially those lining the large
diverticulum protruding from the gut tube, phagocytise food particles
directly, and Branchiostoma can rely on this kind of phagocytic
intracellular digestion to obtain energy throughout all stages of its
life. Gene expression profiles suggest that diverticulum epithelial cells
have functional features of both digestive cells and phagocytes. In
starved Branchiostoma, these cells accumulate endogenous digestive and
hydrolytic enzymes, whereas, when sated, they express many kinds of immune
genes in response to stimulation by phagocytised food particles. We also
found that the distal hindgut epithelium can phagocytise food particles,
but not as many. These results illustrate phagocytic intercellular
digestion in Branchiostoma, explain why. Branchiostoma digestive tract
epithelial cells express typical immune genes, and suggest that the main
physiological function of the Branchiostoma diverticulum is different from
that of the vertebrate liver.