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.

Apoptosis and necrosis during the circadian cycle in the centipede midgut

“…Circadian rhythms in centipedes affect, for example, the ecological niches that they occupy or the homeostasis of the animals (Mead 1970;Amouriq 1967;Lewis 1981;Tuf et al 2006). During our previous studies, we described the proliferation of regenerative cells, which is dependent on (S. cingulata- Chajec et al 2014) or is independent of the day/night cycle (L. forficatus- Chajec et al 2012) as well as the process of autophagy, which proceeded in a continuous manner and did not depend on the day/night cycle (both S. cingulata and L. forficatus) (Rost-Roszkowska et al 2015a). While analyzing the structure and ultrastructure of the endodermal region of the digestive system of the abovementioned species of centipedes (Chajec et al 2012(Chajec et al , 2014, we also observed signs of apoptosis and necrosis.…”

The fine structure of the midgut epithelium in Xerobiotus pseudohufelandi (Iharos, 1966) (Tardigrada, Eutardigrada, Macrobiotidae)

“…Still, it is probable that these cells may divide at specific periods of the life cycle (e.g. during moulting) as has been described or sug- Rost-Roszkowska et al, 2007;Hakim et al, 2010;Nardi et al, 2010;Chajec et al, 2012). Finally, several cells forming the layer of the new/young digestive cells have been observed between crescent-like cells and digestive cells.…”

“…Midgut progenitor cells that differentiate into all types of the midgut epithelial cells have been described mainly for arthropods. They are described as cells which show the features of both midgut stem cells and digestive cells (Martins et al, 2005;Cruz et al, 2011;Chajec et al, 2012). The amount of reserve material (e.g.…”

“…It has been established that encystation and cryptobiosis in tardigrades are adaptive responses to changes in the external environment (Węglarska, 1957;Szymańska, 1995;Wright, 2001;Guidetti et al, 2006Guidetti et al, , 2011Rebecchi et al, , 2009bRebecchi et al, , 2009cWełnicz et al, 2011). However, other potential mechanisms which might be involved in the maintenance of homeostasis in invertebrates, such as apoptosis, self-regeneration of tissues and organs, accumulation of spherites, synthesis of methallothioneins or antioxidants (Parthasarathy and Palli, 2007;Park and Takeda, 2008;Hakim et al, 2010;Rost-Roszkowska et al, 2010a, 2010bChajec et al, 2012), have been studied only in some tardigrade species (Rebecchi et al, 2009a;Rizzo et al, 2010;Bonifacio et al, 2012). In many invertebrates the regenerative properties of the midgut epithelium are also considered as adaptive mechanisms for coping with external stress factors (Wilczek, 2005;Tettamanti et al, 2007;Park and Takeda, 2008;Malagoli et al, 2010;Rost-Roszkowska et al, 2011b;Franzetti et al, 2012).…”

Molecular physiology of digestion in arachnida: functional and comparative-evolutionary approaches.

“…Platyhelminths, Nemertea, Annelida, Mollusca (2), Chelicerata (5) and Crustacea (6, 7) perform both intra and extracellular digestion. Ctenophora, Onycophora, Tardigrada (2), Myriapoda (8,9), Hexapoda (10) and Vertebrata (4) digest the food primarily extracellularly.…”