Submitted to: Poultry Science Association Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2003
Publication Date: July 6, 2003
Citation: Richards, M., Poch, S., Clarke, S., McMurtry, J. 2003. Expression of insulin-like growth factor (IGF) genes in liver and brain tissue during embryonic and post-hatch development of the turkey [abstract]. Poultry Science. v.82 (Suppl 1):81.
Because of their multiple effects on cellular differentiation and metabolism, IGF-I, IGF-II and IGF-I receptor (IGF-IR) are thought to play important roles in regulating the growth and development of avian species. A molecular cloning strategy using primer-directed reverse transcription polymerase chain reaction (RT-PCR) was developed to sequence 1300 bp of a turkey liver-derived cDNA corresponding to the complete coding region and the 5'- and 3'-untranslated regions of the IGF-II mRNA transcript. The turkey IGF-II gene codes for a 187 amino acid pre-proprotein that includes a signal peptide, the mature hormone, and a C-terminal extension peptide comprised of 24, 67 and 96 amino acids, respectively. Turkey IGF-II showed greater than 95% sequence identity at both the nucleotide and amino acid level with chicken IGF-II. The expression of IGF-I, IGF-II and IGF-IR genes was quantified relative to an internal 18S rRNA standard by RT-PCR in liver and whole brain tissue on days 14, 16, 18, 20, 22, 24 and 26 of embryonic development, as well as at hatch (H, day 28) and at 3 wk post-hatching (PH). Expression of liver IGF-I was low throughout embryonic development, but increased more than 10-fold by 3 wk PH. In contrast, IGF-I was expressed in brain tissue at much higher levels than liver throughout development and this level of expression in brain increased gradually, reaching a peak at 3 wk PH. IGF-II was expressed at comparable levels in brain and liver tissue, except for transient increases in liver just prior to H (days 24 and 26) and at 3 wk PH. Expression of IGF-IR declined in brain throughout development reaching its lowest level at 3 wk PH. In liver, IGF-IR expression was lower than that of brain throughout development. An inverse relationship was observed for the expression of IGF-I and IGF-IR genes in brain, but not in liver, through 3 wk PH. Our data suggests differential regulation of IGF gene expression during growth and development of the turkey.