Options
Molecular physiology of the brain and the liver of the African lungfish, Protopterus annectens, during three phases of aestivation
Author
Hiong, Kum Chew
Supervisor
Chew, Shit Fun
Abstract
The African lungfish, Protopterus annectens is an obligate air breather which can survive periods of dry season by undergoing aestivation. The understanding of the mechanisms of aestivation in African lungfishes was previously based on behavioural, biochemical and physiological studies. Hence, this study aims to examine the aestivation-specific gene expression in the brain and liver of P. annectens at different phases of aestivation. By using suppression subtractive hybridisation (SSH) technique, the differential gene expression that occurred during the induction phase (6 days) and prolonged maintenance phase (6 months) of aestivation in air were examined in the brain. During the induction phase, there were changes in genes related to carbohydrate and nitrogen metabolism, cytoprotection, protein synthesis and degradation, transcription, cell proliferation, signalling and metabolic rate reduction in the brain. In the maintenance phase of aestivation, there were also changes in gene expression related to carbohydrate metabolism, protein synthesis, oxidative stress defense, transcription and signaling. Results obtained signified the importance of reconstruction of protein structures in preparation for the maintenance phase of aestivation without an over expenditure of energy and the need to suppress protein degradation and conserve its metabolic fuel stores after entering into the maintenance phase. Differential gene expression during the prolonged maintenance phase and arousal phase (1 day after 6 months of aestivation) were also studied in the liver. Six months of aestivation led to changes in gene expression related to nitrogen metabolism, oxidative stress defense, blood coagulation, complement fixation, iron and copper metabolism and protein synthesis. Similarly during the arousal phase of aestivation, there were changes in gene expression related to nitrogen metabolism, lipid metabolism, fatty acid transport, electron transport system and ATP synthesis. These results indicated that sustaining a low rate of waste production and conservation of energy store were essential during the prolonged aestivation phase. Upon the return of favourable environmental conditions, P. annectens must arouse, excrete the accumulated waste products and feed for repair and growth. Results from the brain SSH led to the study of the Na+/K+-ATPase (nka) and prolactin (prl) genes in the brain and liver. Three isoforms of nka α-subunits and 1 isoform of prl were sequenced from the brain of P. annectens. The mRNA expression of the 3 nka α isoforms were determined in the brain and liver while prl was determined in the brain only by qPCR after the fish was exposed to various phases of aestivation in air or mud or 100 mM NH4Cl. Results showed that mRNA expression of the nka α isoforms and prl were differentially expressed during the different phases of aestivation. Increase in prl at the induction phase of aestivation could be related to increased mucus secretion, increased carbohydrate and lipid metabolism and reconstruction of cells and tissues. There could be a correlation between increase in mRNA expression of prl and nka α1 in the brain during the induction phase. Results obtained from this study suggest a novel role for prl to act as a signal for induction and arousal from aestivation.
Date Issued
2012
Call Number
QL638.3 Hio
Date Submitted
2012