Stivation (Table 2). Taken altogether, these results indicate that the capacity of protein synthesis was not suppressed completely during the prolonged phase of aestivation. This could be an important strategy since the aestivating lungfish would have to maintain the protein synthesis machinery in preparation for arousal from aestivation when water becomes available.Arousal phase: up-regulation of ass1 expression and amino acid metabolismAfter 1 day of arousal from 6 months of aestivation, ass1 still appeared in the forward library (Table 4), indicating that there was a further increase in the mRNA expression of ass1 in the liver. Since cpsIII and fh could not be found in the reverse library (Table 5), and their mRNA expressions were already up-regulated during the maintenance phase of aestivation, it can be deduced that their increased mRNA expressions were sustained into the arousal phase. Upon arousal, the fish has to reconstruct cells and tissues that have been modified during the induction phase and repair damages that have occurred during the maintenance phase of aestivation. Such structural changes would require increased syntheses of certain proteins, and since SP600125 custom synthesis refeeding would not occur until 7?0 days after arousal, it would imply the mobilization of amino acids of endogenous origin [12]. Both substrate and energy are needed for repair and regeneration. Our results indicate that endogenous amino acids could serve such purposes during arousal. Indeed, there could be increases in the capacity of protein turnover, the electron transport system, lipid biosynthesis and iron metabolism in P. annectens after 1 day of arousal from 6 months of aestivation. The energy that supports these activities could be derived from increased amino acid (and perhaps also carbohydrate) catabolism during this period. The ammonia released through increased amino acid catabolism had to be detoxified to urea through the hepatic OUC. Therefore, it can be understood why there were significant increases in the urea-synthesizing capacity upon arousal from aestivation. Besides being involved in urea synthesis, arginine produced by Ass also acts as a substrate for nitric oxide (NO) production in the liver, where NO is involved in liver regeneration [55] and protection of the liver from ischaemia eperfusion injury [56]. Indeed, Chng et al [57] had shown that the arginine and NOx concentrations decreased and increased, respectively, in the liver of P. annectens after 6 months of aestivation and after 3 days of arousal from aestivation, supporting the proposition that arginine synthesized through Ass could be used for increased NO production, especially during arousal.Arousal phase: up-regulation of carbohydrate metabolism?Compared with the maintenance phase, 1 day of arousal led to increases in mRNA expressions of gapdh and aldob, and a decrease in the expression of another isoform of aldob. Although Gapdh does not catalyse a flux generating step (unlike hexokinase, ICG-001 side effects glycogen phosphorylase,PLOS ONE | DOI:10.1371/journal.pone.0121224 March 30,21 /Differential Gene Expression in the Liver of the African Lungfishand pyruvate kinase) or act as a regulatory enzyme (unlike phosphofructokinase) in the glycolytic pathway, it involves an oxidation-reduction reaction, and our results could indicate a tendency towards an up-regulation of carbohydrate metabolism in the liver of P. annectens during the arousal phase of aestivation. Frick et al. [58] reported that P. dolloi cons.Stivation (Table 2). Taken altogether, these results indicate that the capacity of protein synthesis was not suppressed completely during the prolonged phase of aestivation. This could be an important strategy since the aestivating lungfish would have to maintain the protein synthesis machinery in preparation for arousal from aestivation when water becomes available.Arousal phase: up-regulation of ass1 expression and amino acid metabolismAfter 1 day of arousal from 6 months of aestivation, ass1 still appeared in the forward library (Table 4), indicating that there was a further increase in the mRNA expression of ass1 in the liver. Since cpsIII and fh could not be found in the reverse library (Table 5), and their mRNA expressions were already up-regulated during the maintenance phase of aestivation, it can be deduced that their increased mRNA expressions were sustained into the arousal phase. Upon arousal, the fish has to reconstruct cells and tissues that have been modified during the induction phase and repair damages that have occurred during the maintenance phase of aestivation. Such structural changes would require increased syntheses of certain proteins, and since refeeding would not occur until 7?0 days after arousal, it would imply the mobilization of amino acids of endogenous origin [12]. Both substrate and energy are needed for repair and regeneration. Our results indicate that endogenous amino acids could serve such purposes during arousal. Indeed, there could be increases in the capacity of protein turnover, the electron transport system, lipid biosynthesis and iron metabolism in P. annectens after 1 day of arousal from 6 months of aestivation. The energy that supports these activities could be derived from increased amino acid (and perhaps also carbohydrate) catabolism during this period. The ammonia released through increased amino acid catabolism had to be detoxified to urea through the hepatic OUC. Therefore, it can be understood why there were significant increases in the urea-synthesizing capacity upon arousal from aestivation. Besides being involved in urea synthesis, arginine produced by Ass also acts as a substrate for nitric oxide (NO) production in the liver, where NO is involved in liver regeneration [55] and protection of the liver from ischaemia eperfusion injury [56]. Indeed, Chng et al [57] had shown that the arginine and NOx concentrations decreased and increased, respectively, in the liver of P. annectens after 6 months of aestivation and after 3 days of arousal from aestivation, supporting the proposition that arginine synthesized through Ass could be used for increased NO production, especially during arousal.Arousal phase: up-regulation of carbohydrate metabolism?Compared with the maintenance phase, 1 day of arousal led to increases in mRNA expressions of gapdh and aldob, and a decrease in the expression of another isoform of aldob. Although Gapdh does not catalyse a flux generating step (unlike hexokinase, glycogen phosphorylase,PLOS ONE | DOI:10.1371/journal.pone.0121224 March 30,21 /Differential Gene Expression in the Liver of the African Lungfishand pyruvate kinase) or act as a regulatory enzyme (unlike phosphofructokinase) in the glycolytic pathway, it involves an oxidation-reduction reaction, and our results could indicate a tendency towards an up-regulation of carbohydrate metabolism in the liver of P. annectens during the arousal phase of aestivation. Frick et al. [58] reported that P. dolloi cons.
