Protozoa are the ancestors of the Metazoa. This link between Protozoa and Metazoa is noticeable at the cellular level, since several cytoplasmic organelles and signal molecules: such as neurotransmitters are common to both of them. The typical functions of animals: such as nutrition, respiration, excretion, motility and reproduction are also present in these unicellular eukaryotic organisms. The ciliate protozoa Paramecium primaurelia is known as a model organism for studies on vesicular trafficking (FOK and ALLEN, 1990). Recently, the role of transmembrane channel proteins permeable to water, named aquaporins (AQPs) has been described in human exocytotic vacuoles: such as synaptic vesicles and pancreatic zymogen granules (JENA, 2006). In our work, we investigated the presence of molecules immunologically related to mouse AQP2, during the logarithmic growth phase of P. primaurelia. We identified the presence of an AQP2-like protein localized near the macronucleus and both the young and the nascent phagosome, though the immune staining was not present around the vacuoles in the advanced stages of cyclosis. This protein has an apparent molecular mass of approximately 35 kDa, which is within the range of AQPS most frequently observed in mammals (25 kDa - 38 kDa) (HERRERA and GARVIN, 2011). Our data suggest the presence of the AQP2-like protein on the membrane of acidosomes, vesicle able to acidify the phagosome, allowing the prey killing and the denaturation of its proteins (FOK and ALLEN, 2000). The exposure of Paramecium to sub-lethal concentrations of silver (AQPs inhibitor) as well as colchicine and acridine orange highlights how the AQP2 of P. primaurelia is inserted into the acidosome membrane by Golgi apparatus and play a role in the maintaining of the acidosomes homeostasis, allowing their fusion with the phagosome. These results evidence that in mammals the role of AQPs associated with intracellular vesicles has not been acquired during evolution, unlike what was supposed in the past. Probably, they have been inherited from their unicellular eukaryotic ancestors, protozoa. Additionally, the first description of an AQP2-like protein in P. primaurelia, model organism for studies on phagocytosis and exocytosis, provides a solid foundation to expand our knowledge on the controversial role of intracellular AQPs inside animal cells and, not least, humans.
ROLE OF A PROTEIN RELATED TO AQUAPORIN-2 IN THE DIGESTIVE PROCESS OF PARAMECIUM PRIMAURELIA (PROTOZOA)
MILLO E;AMAROLI A
2014-01-01
Abstract
Protozoa are the ancestors of the Metazoa. This link between Protozoa and Metazoa is noticeable at the cellular level, since several cytoplasmic organelles and signal molecules: such as neurotransmitters are common to both of them. The typical functions of animals: such as nutrition, respiration, excretion, motility and reproduction are also present in these unicellular eukaryotic organisms. The ciliate protozoa Paramecium primaurelia is known as a model organism for studies on vesicular trafficking (FOK and ALLEN, 1990). Recently, the role of transmembrane channel proteins permeable to water, named aquaporins (AQPs) has been described in human exocytotic vacuoles: such as synaptic vesicles and pancreatic zymogen granules (JENA, 2006). In our work, we investigated the presence of molecules immunologically related to mouse AQP2, during the logarithmic growth phase of P. primaurelia. We identified the presence of an AQP2-like protein localized near the macronucleus and both the young and the nascent phagosome, though the immune staining was not present around the vacuoles in the advanced stages of cyclosis. This protein has an apparent molecular mass of approximately 35 kDa, which is within the range of AQPS most frequently observed in mammals (25 kDa - 38 kDa) (HERRERA and GARVIN, 2011). Our data suggest the presence of the AQP2-like protein on the membrane of acidosomes, vesicle able to acidify the phagosome, allowing the prey killing and the denaturation of its proteins (FOK and ALLEN, 2000). The exposure of Paramecium to sub-lethal concentrations of silver (AQPs inhibitor) as well as colchicine and acridine orange highlights how the AQP2 of P. primaurelia is inserted into the acidosome membrane by Golgi apparatus and play a role in the maintaining of the acidosomes homeostasis, allowing their fusion with the phagosome. These results evidence that in mammals the role of AQPs associated with intracellular vesicles has not been acquired during evolution, unlike what was supposed in the past. Probably, they have been inherited from their unicellular eukaryotic ancestors, protozoa. Additionally, the first description of an AQP2-like protein in P. primaurelia, model organism for studies on phagocytosis and exocytosis, provides a solid foundation to expand our knowledge on the controversial role of intracellular AQPs inside animal cells and, not least, humans.
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