Ultrastructure and regeneration of midgut epithelial cells in Lithobius forficatus (Chilopoda, Lithobiidae)
Abstract
Lithobius forficatus (Myriapoda, Chilopoda, Lithobiidae) is a widespread species of centipede that is common across Europe. Its midgut epithelial cells are an important line of defense against toxic substances that originate in food, such as pathogens and metals.
Despite this important role, the biology of the midgut epithelium is not well known. Here we describe the ultrastructure of the midgut epithelium, as well as the replacement of degenerated midgut epithelial cells.
The midgut epithelium of L. forficatus is composed of digestive, secretory, and regenerative cells. The cytoplasm of digestive cells shows regionalization in organelle distribution, which is consistent with the role of these cells in secretion of enzymes, absorption of nutrients, and accumulation of lipids and glycogen.
Secretory cells, which do not reach the luminal surface of the midgut epithelium, possess numerous electron-dense and electron-lucent granules and may have an endocrine function. Hemidesmosomes anchor secretory cells to the basal lamina.
Regenerative cells play the role of midgut stem cells, as they are able to proliferate and differentiate. Their proliferation occurs in a continuous manner, and their progeny differentiate only into digestive cells.
The regeneration of secretory cells was not observed. Mitotic divisions of regenerative cells were confirmed using immunolabeling against BrdU and phosphohistone H3.
Hemocytes associate with the midgut epithelium, accumulating between the visceral muscles and beneath the basal lamina of the midgut epithelium. Hemocytes also occur among the digestive cells of the midgut epithelium in animals infected with Rickettsia-like microorganisms.
These hemocytes presumably have an immunoprotective function in the midgut.