Erum proteins, which is synthesized mainly in liver and plays a crucial role in iron metabolism. Under normal conditions, most of the iron in the plasma is bound to transferrin, and iron-transferrin complexes enter the cells via a transferrin receptor-mediated endocytic pathway. Transferrin also has a close relationship with the immune system. It binds to iron, creating an environment with low levels of iron, where few microorganisms can survive and prosper [45]. On the other hand, ferritin is the main iron storage GSK-1605786 site protein in both eukaryotes and prokaryotes; it keeps iron in a soluble and non-toxic form [43,46,47]. Also, up-regulation of ferritin has been observed in oxidative stress [48] and inflammatory conditions in human [49?1]. Transferrin and ferritin mRNA expression levels are up-regulated in P. annectens during the induction phase of aestivation [13], probably due to oxidative stress and inflammation arisen through tissue reconstruction, and/or a high turnover rate of free and bound iron resulting from increased production of certain types of hemoglobins or hemoglobin in general. By contrast, our results indicated that there could be a decrease in the capacity of iron metabolism and transport in P. annectens during the maintenance phase of aestivation as transferrin (14 clones) and hemopexin (3 clones) appeared in the reverse library. This correlated well with the aestivation process as a prolonged torpor state would theoretically lead to a lower rate of ROS production, and stabilized expression of hemoglobin genes.Maintenance phase: down-regulation of genes related to copper metabolismCeruloplasmin (CP) is crucial in the oxidation of Fe2+ to Fe3+, which enables the binding of iron to transferrin, facilitating the mobilization of iron in the body. It also represents a tightly bound pool of copper that accounts for >90 of the total plasma copper in most species [52,53]. CP synthesis and/or secretion can be altered by inflammation, hormones, and copper. Plasma concentrations of acute-phase globulins, including CP, increase with tissue injury, localized acute inflammation, and chronic inflammatory diseases [54]. The mRNA expression level of cp was up-regulated in the liver of P. annectens during the induction phase of aestivation [13]. ABT-737 supplier However, our results revealed that 6 months of aestivation led to a down-regulation of cp mRNA expression in the liver of P. annectens. This suggested that tissue degradation or inflammation may be limited during the maintenance phase of aestivation due to a profoundPLOS ONE | DOI:10.1371/journal.pone.0121224 March 30,20 /Differential Gene Expression in the Liver of the African Lungfishdecrease in metabolic activity. Consequently, there was no longer a need to up-regulate expression level of cp.Maintenance phase: up- or down-regulation of protein synthesis?Twelve genes related to protein synthesis, transport and folding appeared in the reverse library of lungfish undergoing 6 months of aestivation in air (Table 3). The down-regulation of genes related to protein synthesis such as eukaryotic translation initiation factors and other ribosomal proteins is a consistent phenomenon in metabolic rate reduction. Suppression of protein synthesis during aestivation would help the animal to conserve energy and enhance its survival. However, 10 types of ribosomal proteins appeared in the forward library indicating up-regulation of mRNA expressions of these genes in the liver of P. annectens after 6 months of ae.Erum proteins, which is synthesized mainly in liver and plays a crucial role in iron metabolism. Under normal conditions, most of the iron in the plasma is bound to transferrin, and iron-transferrin complexes enter the cells via a transferrin receptor-mediated endocytic pathway. Transferrin also has a close relationship with the immune system. It binds to iron, creating an environment with low levels of iron, where few microorganisms can survive and prosper [45]. On the other hand, ferritin is the main iron storage protein in both eukaryotes and prokaryotes; it keeps iron in a soluble and non-toxic form [43,46,47]. Also, up-regulation of ferritin has been observed in oxidative stress [48] and inflammatory conditions in human [49?1]. Transferrin and ferritin mRNA expression levels are up-regulated in P. annectens during the induction phase of aestivation [13], probably due to oxidative stress and inflammation arisen through tissue reconstruction, and/or a high turnover rate of free and bound iron resulting from increased production of certain types of hemoglobins or hemoglobin in general. By contrast, our results indicated that there could be a decrease in the capacity of iron metabolism and transport in P. annectens during the maintenance phase of aestivation as transferrin (14 clones) and hemopexin (3 clones) appeared in the reverse library. This correlated well with the aestivation process as a prolonged torpor state would theoretically lead to a lower rate of ROS production, and stabilized expression of hemoglobin genes.Maintenance phase: down-regulation of genes related to copper metabolismCeruloplasmin (CP) is crucial in the oxidation of Fe2+ to Fe3+, which enables the binding of iron to transferrin, facilitating the mobilization of iron in the body. It also represents a tightly bound pool of copper that accounts for >90 of the total plasma copper in most species [52,53]. CP synthesis and/or secretion can be altered by inflammation, hormones, and copper. Plasma concentrations of acute-phase globulins, including CP, increase with tissue injury, localized acute inflammation, and chronic inflammatory diseases [54]. The mRNA expression level of cp was up-regulated in the liver of P. annectens during the induction phase of aestivation [13]. However, our results revealed that 6 months of aestivation led to a down-regulation of cp mRNA expression in the liver of P. annectens. This suggested that tissue degradation or inflammation may be limited during the maintenance phase of aestivation due to a profoundPLOS ONE | DOI:10.1371/journal.pone.0121224 March 30,20 /Differential Gene Expression in the Liver of the African Lungfishdecrease in metabolic activity. Consequently, there was no longer a need to up-regulate expression level of cp.Maintenance phase: up- or down-regulation of protein synthesis?Twelve genes related to protein synthesis, transport and folding appeared in the reverse library of lungfish undergoing 6 months of aestivation in air (Table 3). The down-regulation of genes related to protein synthesis such as eukaryotic translation initiation factors and other ribosomal proteins is a consistent phenomenon in metabolic rate reduction. Suppression of protein synthesis during aestivation would help the animal to conserve energy and enhance its survival. However, 10 types of ribosomal proteins appeared in the forward library indicating up-regulation of mRNA expressions of these genes in the liver of P. annectens after 6 months of ae.
