Abstract
Nutritional regulation of gene expression associated with growth and feeding behavior in avian species can become an important technique to improve poultry production according to the supply of nutrients in the diet. Insulin-like growth factor-I (IGF-I) found in chickens has been characterized to be a 70 amino acid polypeptide and plays an important role in growth and metabolism. Although it is been well known that IGF-I is highly associated with embryonic development and post-hatching growth, changes in the distribution of IGF-I gene expression throughout early- to late-embryogenesis have not been studied so far. We revealed that the developmental pattern of IGF-I gene expression during embryogenesis differed among various tissues. No bands of IGF-I mRNA were detected in embryonic liver at 7 days of incubation, and thereafter the amount of hepatic IGF-I mRNA was increased from 14 to 20 days of incubation. In eyes, a peak in IGF-I mRNA levels occurred at mid-embryogenesis, but by contrast, IGF-I mRNA was barely detectable in the heart throughout all incubation periods. In the muscle, no significant difference in IGF-I gene expression was observed during different stages of embryogenesis. After hatching, hepatic IGF-I gene expression as well as plasma IGF-I concentration increases rapidly with age, reaches a peak before sexual maturity, and then declines. The IGF-I gene expression is very sensitive to changes in nutritional conditions. Food-restriction and fasting decreased hepatic IGF-I gene expression and refeeding restored IGF-I gene expression to the level of fed chickens. Dietary protein is also a very strong factor in changing hepatic IGF-I gene expression. Refeeding with dietary protein alone successfully restored hepatic IGF-I gene expression of fasted chickens to the level of fed controls. In most circumstances, IGF-I makes a complex with specific high-affinity IGF-binding proteins (IGFBPs). So far, four different IGFBPs have been identified in avian species and the major IGFBP in chicken plasma has been reported to be IGFBP-2. We studied the relationship between nutritional status and IGFBP-2 gene expression in various tissues of young chickens. In the liver of fed chickens, almost no IGFBP-2 mRNA was detected. However, fasting markedly increased hepatic IGFBP-2 gene expression, and the level was reduced after refeeding. In the gizzard of well-fed young chickens, IGFBP-2 gene expression was detected and fasting significantly elevated gizzard IGFBP-2 mRNA levels to about double that of fed controls. After refeeding, gizzard IGFBP-2 gene expression decreased similar to hepatic IGFBP-2 gene expression. In the brain, IGFBP-2 mRNA was observed in fed chickens and had significantly decreased by fasting. In the kidney, IGFBP-2 gene expression was observed but not influenced by fasting and refeeding. Recently, we have demonstrated in vivo that gizzard and hepatic IGFBP-2 gene expression in fasted chickens was rapidly reduced by intravenous administration of insulin, as indicated that in young chickens the reduction in gizzard and hepatic IGFBP-2 gene expression in vivo stimulated by malnutrition may be, in part, regulated by means of the increase in plasma insulin concentration via an insulin-response element. The influence of dietary protein source (isolated soybean protein vs. casein) and the supplementation of essential amino acids on gizzard IGFBP-2 gene expression was examined. In both soybean protein and casein diet groups, the deficiency of essential amino acids stimulated chickens to increase gizzard IGFBP-2 gene expression. Although amino acid supplementation of a soybean protein diet significantly decreased gizzard IGFBP-2 mRNA levels, a similar reduction was not observed in chickens fed a casein diet supplemented with amino acids. This overview of nutritional regulation of IGF-I and IGFBP-2 gene expression in young chickens would serve for the establishment of the supply of nutrients to diets to improve poultry production. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 5 : 747- 754)
Highlights
It has been well recognized that growth hormone (GH) KITA ET AL.Hypothalamus in chicken plasma differs from that in human plasma SomatostatinGrowth hormonereleasing hormoneAnterior pituitaryGhrelin (Armstrong et al, 1989; Francis et al, 1990; Schoen et al, 1992; Upton et al, 1992; Morishita et al, 1993)
We studied the relationship between nutritional status IGFBP-2 and revealed that it contained insulin response and IGFBP-2 gene expression in various tissues of chickens element in the 5' upstream region
The response of hepatic increased by 2 day-fasting was rapidly reduced by IGFBP-2 gene expression to fasting and refeeding intravenous administration of bovine insulin in young suggested two contrary functions of IGFBP-2 in plasma. chickens (Nagao et al, 2001). These results indicated that in Recently Hoeflich et al (1999) made transgenic mice young chickens the reduction in gizzard and hepatic carrying mouse IGFBP-2 gene and revealed that IGFBP-2 gene expression in vivo stimulated by malnutrition overexpression of IGFBP-2 regulated postnatal growth might be, in part, regulated by means of the increase in negatively, potentially by reducing the bioavailavility of plasma insulin concentration via an insulin-response
Summary
Ghrelin (Armstrong et al, 1989; Francis et al, 1990; Schoen et al, 1992; Upton et al, 1992; Morishita et al, 1993). Using the labeled chicken IGF-I as probe, a 30 kDa band in plasma samples from well-fed chickens was not detected. In plasma from chickens given restricted food intake or a Growth hormone low protein diet an intense band was observed at 30 kDa. The absence of the 30 kDa IGFBP in plasma of well-fed. Liver chickens indicated that chicken IGFBP-2 protein was Stomach produced when nutritional status was inadequate Insulin-like et al, 1993; Kita et al, 1996b). Chicken IGFBP-2 cDNA growth factor-I and gene were cloned and the tissue distribution of IGFBP-
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