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. 2013 Aug 16;8(8):e71205.
doi: 10.1371/journal.pone.0071205. eCollection 2013.

Differential gene expression in the brain of the African lungfish, Protopterus annectens, after six days or six months of aestivation in air

Kum C Hiong  1 , Yuen K Ip, Wai P Wong, Shit F Chew
Affiliations

Differential gene expression in the brain of the African lungfish, Protopterus annectens, after six days or six months of aestivation in air

Kum C Hiong et al. PLoS One. .

Abstract

The African lungfish, Protopterus annectens, can undergo aestivation during drought. Aestivation has three phases: induction, maintenance and arousal. The objective of this study was to examine the differential gene expression in the brain of P. annectens during the induction (6 days) and maintenance (6 months) phases of aestivation as compared with the freshwater control using suppression subtractive hybridization. During the induction phase of aestivation, the mRNA expression of prolactin (prl) and growth hormone were up-regulated in the brain of P. annectens, which indicate for the first time the possible induction role of these two hormones in aestivation. Also, the up-regulation of mRNA expression of tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein γ polypeptide and the down-regulation of phosphatidylethanolamine binding protein, suggest that there could be a reduction in biological and neuronal activities in the brain. The mRNA expression of cold inducible RNA-binding protein and glucose regulated protein 58 were also up-regulated in the brain, probably to enhance their cytoprotective effects. Furthermore, the down-regulation of prothymosin α expression suggests that there could be a suppression of transcription and cell proliferation in preparation for the maintenance phase. In general, the induction phase appeared to be characterized by reduction in glycolytic capacity and metabolic activity, suppression of protein synthesis and degradation, and an increase in defense against ammonia toxicity. In contrast, there was a down-regulation in the mRNA expression of prl in the brain of P. annectens during the maintenance phase of aestivation. In addition, there could be an increase in oxidative defense capacity, and up-regulation of transcription, translation, and glycolytic capacities in preparation for arousal. Overall, our results signify the importance of reconstruction of protein structures and regulation of energy expenditure during the induction phase, and the needs to suppress protein degradation and conserve metabolic fuel stores during the maintenance phase of aestivation.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. qRT-PCR of selected genes that were differentially expressed based on suppression subtractive hybridization.
Relative quantification of mRNA expression (fold change) of (A) pyruvate kinase (pk, JZ347493), (B) glutamine synthetase (gs, JZ347462), (C) fumarate hydratase (fh, JZ347458), (D) prolactin (prl, JZ347487), (E) phosphofructokinase (pfk, JZ347479), (F) Na+/K+-ATPase α2 (nkaα2, JZ347474), (G) pyruvate kinase (pk, JZ347493), (H) prolactin (prl, JZ347487) and (I) ferritin heavy chain (fth, JZ347374), using β-actin as the reference gene, in the brain of Protopterus annectens aestivated for 6 days (d) (A–F) or 6 months (G–I) in air with reference to the those of fish kept in freshwater as control. Results represent mean+S.E.M. (N = 6). *Significantly different from the corresponding freshwater control (P<0.05).
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References

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Grants and funding

This project was supported by the Ministry of Education of the Republic of Singapore through grants, (R-154-000-429-112 and R154-000-470-112) and (RI 9/08 CSF and RI 4/12 CSF), administered to Y. K. Ip and S. F. Chew, respectively. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding was received for this study.

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