Chicken ghrelin: purification, cDNA cloning, and biological activity

Area of Science:

• Endocrinology
• Comparative Physiology
• Molecular Biology

Background:

• Ghrelin is a peptide hormone primarily known for regulating growth hormone (GH) secretion and appetite.
• Understanding ghrelin's role in avian species provides insights into its evolutionary conservation and functional divergence.

Purpose of the Study:

• To isolate, clone, and characterize ghrelin from the chicken (Gallus gallus).
• To investigate the physiological effects of chicken ghrelin on growth hormone and adrenal function in avian and mammalian models.

Main Methods:

• Purification and cDNA cloning of chicken ghrelin.
• Sequence analysis and comparison with mammalian ghrelin.
• Reverse transcription polymerase chain reaction (RT-PCR) for gene expression analysis.
• Administration of synthetic chicken ghrelin to rats and chicks to measure plasma GH and corticosterone levels.

Main Results:

• Chicken ghrelin consists of 26 amino acids with 54% sequence identity to human ghrelin, featuring a conserved acylated Ser(3) residue.
• Chicken ghrelin mRNA is primarily expressed in the proventriculus region of the stomach, with lower levels in the brain, lung, and intestine.
• Chicken ghrelin effectively stimulated GH secretion in both rats and chicks, comparable to mammalian ghrelin.
• Chicken ghrelin administration increased plasma corticosterone levels in chicks at a lower dose than observed in mammals.

Conclusions:

• The stimulatory effect of ghrelin on growth hormone secretion is evolutionarily conserved across species.
• Chicken ghrelin exhibits a unique effect on adrenal function, distinct from its role in mammals.
• This study elucidates the molecular and physiological characteristics of avian ghrelin, highlighting conserved and divergent functions.