Submitted on July 11, 2007
Accepted on September 25, 2007
Molecular mechanisms underlying the development of endothermy in birds (Gallus gallus): a new role of PGC-1
?
Isabel Walter1* and Frank Seebacher1
1 Biological Sciences, University of Sydney, Sydney, New South Wales, Australia
* To whom correspondence should be addressed. E-mail: iwal9728{at}usyd.edu.au.
In endotherms, plasticity of internal heat production in response to environmental variability is an important component of thermoregulation. During embryogenesis endotherms cannot regulate their body temperature metabolically and are therefore similar to ectotherms. The transition from ectothermy to endothermy occurs by the development of metabolic capacity during embryogenesis. Here we test the hypothesis that the development of metabolism during embryogenesis in birds is under transcriptional control and that metabolic capacity is upregulated in colder environments. The peroxisome-proliferator-activated receptor- 
coactivator-1
(PGC-1) is the major metabolic regulator in mammals. PGC-1 and its target PPAR were significantly elevated during development in pectoral muscle and liver of chickens (Gallus gallus) compared to adults. However, the timing of upregulation of PGC-1 and PPAR was not in synchrony. In cool incubation temperatures (35°C) both PGC-1 and PPAR gene expression was increased in liver but not in skeletal muscle, compared to a 38°C incubation treatment. Cytochrome c oxidase and citrate synthase enzyme activities and ATPsynthase gene expression increased during embryonic development in liver and muscle, and there was a significant effect of incubation temperature on these parameters. Our findings suggest that PGC-1might be important for establishing endothermic metabolic capacity during embryogenesis in birds.
