The process of autophagy has been detected in the midgut epithelium of four millipede species: Julus scandinavius, Polyxenus lagurus, Archispirostreptus gigas, and Telodeinopus aoutii. It has been examined using transmission electron microscopy (TEM), which enabled differentiation of cells in the midgut epithelium, and some histochemical methods (light microscope and fluorescence microscope). While autophagy appeared in the cytoplasm of digestive, secretory, and regenerative cells in J. scandinavius and A. gigas, in the two other species, T. aoutii and P. lagurus, it was only detected in the digestive cells. Both types of macroautophagy, the selective and nonselective processes, are described using TEM. Phagophore formation appeared as the first step of autophagy. After its blind ends fusion, the autophagosomes were formed. The autophagosomes fused with lysosomes and were transformed into autolysosomes. As the final step of autophagy, the residual bodies were detected. Autophagic structures can be removed from the midgut epithelium via, e.g., atypical exocytosis. Additionally, in P. lagurus and J. scandinavius, it was observed as the neutralization of pathogens such as Rickettsia-like microorganisms. Autophagy and apoptosis ca be analyzed using TEM, while specific histochemical methods may confirm it.

The middle region of the digestive system, the midgut of freshwater shrimp Neocaridina davidi is composed of a tube-shaped intestine and the hepatopancreas formed by numerous caeca. Two types of cells have been distinguished in the intestine, the digestive cells (D-cells) and regenerative cells (R-cells). The hepatopancreatic tubules have three distinct zones distinguished along the length of each tubule—the distal zone with R-cells, the medial zone with differentiating cells, and the proximal zone with F-cells (fibrillar cells) and B-cells (storage cells). Fasting causes activation of cell death, a reduction in the amount of reserve material, and changes in the mitochondrial membrane potential. However, here we present how the concentration of ROS changes according to different periods of fasting and whether re-feeding causes their decrease. In addition, the activation/deactivation of mitochondrial superoxide dismutase (MnSOD) was analyzed. The freshwater shrimps Neocaridina davidi (Crustacea, Malacostraca, Decapoda) were divided into experimental groups: animals starved for 14 days, animals re-fed for 4, 7, and 14 days. The material was examined using the confocal microscope and the flow cytometry. Our studies have shown that long-term starvation increases the concentration of free radicals and MnSOD concentration in the intestine and hepatopancreas, while return to feeding causes their decrease in both organs examined. Therefore, we concluded that a distinct relationship between MnSOD concentration, ROS activation, cell death activation and changes in the mitochondrial membrane potential occurred.

No abstract

Neocaridina davidi is a freshwater shrimp that originates from Taiwan and is commonly bred all over the word. Like all decapods, which develop indirectly, this species has pelagic larvae that may differ entirely in their morphology and habits from adult specimens. To fill a gap of knowledge about the developmental biology of freshwater shrimps we decided to document the 3D-localization of the midgut inside the body cavity of larval stages of N. davidi using X-ray microtomography, and to describe all structural and ultrastructural changes of the midgut epithelium (intestine and hepatopancreas) which occur during postembryonic development of N. davidi using light and transmission electron microscopy. We laid emphasis on stem cell functioning and cell death processes connected with differentiation. Our study revealed that while the intestine in both larval stages of N. davidi has the form of a fully developed organ, which resembles that of adult specimens, the hepatopancreas undergoes elongation and differentiation. E-cells, which are midgut stem cells, due to their proliferation and differentiation are responsible for the above-mentioned processes. Our study revealed that apoptosis is a common process in both larval stages of N. davidi in the intestine and proximal region of the hepatopancreas. In zoea III, autophagy as a survival factor is activated in order to protect cells against their death. However, when there are too many autophagic structures in epithelial cells, necrosis as passive cell death is activated. The presence of all types of cell death in the midgut in the zoea III stage confirms that this part of the digestive tract is fully developed and functional. Here, we present the first description of apoptosis, autophagy and necrosis in the digestive system of larval stages of Malacostraca and present the first description of their hepatopancreas elongation and differentiation due to midgut stem cell functioning.

No abstract