Molecular mechanisms underlying the development of endothermy in birds (Gallus gallus): a new role of PGC-1 alpha?

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-gamma (PPAR gamma) coactivator-1 alpha (PGC-1 alpha) is the major metabolic regulator in mammals. PGC-1 alpha and its target PPAR gamma were significantly elevated during development in pectoral muscle and liver of chickens (Gallus gallus) compared with adults. However, the timing of upregulation of PGC-1 alpha and PPAR gamma was not in synchrony. In cool incubation temperatures (35 degrees C) both PGC-1 alpha and PPAR gamma gene expression was increased in liver but not in skeletal muscle, compared with a 38 degrees C incubation treatment. Cytochrome c oxidase and citrate synthase enzyme activities and ATP synthase 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-1 alpha might be important for establishing endothermic metabolic capacity during embryogenesis in birds.