DEVELOPMENTAL-CHANGES IN SERUM INSULIN-LIKE GROWTH-FACTOR-I AND INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN THE TURKEY EMBRYO

The ontogeny of insulin-like growth factor-I (IGF-I) and ontogeny as w ell as the molecular nature of the insulin-like growth factor binding proteins (IGFBP) as they relate to embryogenesis and posthatch growth in the turkey have not been reported. In this study, serum samples wer e harvested from turkey embryos incubated under shell-less and shelled conditions from Day 12 to 28 of incubation. Samples from 3, 6, and 8 wk posthatch were also evaluated. Significant changes in serum IGF-I i n shelled embryos were observed in that IGF-I was low in early incubat ion, peaked at mid-incubation, and returned to levels equivalent to ea rly incubation at hatching. No mid-embryogenesis (Days 14 to 18) incre ase in serum IGF-I was noted in the shell-less cultures. Embryo weight s diverge at Day 18 of incubation, with shell-less embryos being signi ficantly lighter than their age-matched shelled embryos, suggesting a possible relationship between total circulating IGF-I and body weight gain. Three distinct IGFBP were identified in serum from turkey embryo s, exhibiting molecular weights of 27, 29, and 69 kDa. During embryoni c development, the 29 kDa IGFBP appeared to be the predominant species , with levels peaking on Day 24 of incubation, and being minimally det ectable at hatching. Ontogeny of the 29 kDa IGFBP was similar in the s helled and shell-less embryos. The 69-kDa IGFBP-Like protein did not a ppear in the circulation until late in embryogenesis, Day 22 in shell- less and Day 26 in shelled embryos. The 27-kDa IGFBP appeared in late incubation. Similar IGFBP (28, 30, and 69 kDa) were observed in the gr owing male turkey. The 69-kDa protein did not vary across ages studied , whereas the 28-kDa IGFBP appeared to increase with age. This is the first report describing serum IGF-I and IGFBP in the developing turkey . Turkey IGFBP appear to be regulated by independent events during inc ubation and posthatch growth.