Ontogeny and effect of weaning on mRNA levels of IGFs, EGF and bFGF in various tissues of the pig
In the present study, we have examined three growth factors which can be important for organ development of pancreas, liver, kidney and muscle. We believe that these growth factors are involved in the growth of these tissues. These growth factors are the insulin like growth factor-I and -II (IGFs), the epidermal growth factor (EGF) and the basic fibroblast growth factor (bFGF). We have measured the messenger RNA (mRNA) levels of these growth factors and those of their receptors (R) as well as IGF binding proteins (IGFBPs) from fetal life to 180 days of age.In the case of IGFs and IGFBPs, concentrations in the serum and in each tissue were also measured. The IGFs and IGFBPs serum concentrations increased with advancing age, the IGFBP-3 being the major IGF binding protein in serum during postnatal life.In the pancreas, IGF-I mRNA levels were high during the fetal and early postnatal life. Around the weaning period (21 days of age), tissue concentration of IGF-I reached a maximal level which was concomitant with a high IGF-I mRNA level and an increased activity of pancreatic enzymes. Pancreatic IGF-II and IGFI-R mRNA levels as well as IGF-II tissue concentrations were high in fetuses and were accompanied by a rapid growth period of pancreas in fetuses of 90 days of age. Levels of EGF, EGFR and bFGF mRNAs were higher during the fetal life than after birth. These results imply that multiple growth factors are involved in fetal pancreatic development. At 27 and 30 days of age, EGF mRNA levels were higher in weaned than in suckling piglets, suggesting a possible involvement of EGF in pancreatic development during the weaning period. In the liver, IGF-I mRNA level paralleled its tissue concentration. High tissue concentration of both IGF-I and -II at 1 and 21 days of age corresponded to an accelerated growth period of the liver. The IGFBP-1 mRNA level was the most abundant in the liver when compared to that of other tissues.In the liver, abundant EGFR mRNA level was observed whereas EGF mRNA was undetected. The bFGF mRNA levels were high over the whole developmental period. In the kidney, IGFs mRNA levels were high in fetuses while kidney IGFs concentrations peaked in newborns, which were associated with a fast growth period of this organ. As observed in the liver, the bFGF mRNA was abundant in the kidney during the whole developmental period, while EGF mRNA level increased with development. In the skeletal muscle, IGF-I, IGF-II, IGF-IR, IGFBP-3 and bFGF mRNAs were all abundant during fetal and neonatal life. The EGF mRNA level increased during development. These data suggest that IGFs, EGF and bFGF are likely physiological regulators of growth and maintenance of the skeletal muscle. In conclusion, mRNA levels and concentrations of growth factors and their binding proteins are tissue and developmentally regulated. Concentrations and mRNA levels of IGFs, IGFRs and IGFBPs are coordinately regulated in the pancreas and liver. Fast growth periods of pancreas, liver and kidney are accompanied by high concentrations of IGFs and abundant mRNA levels of IGFs, EGF and bFGF, suggesting that these growth factors are important regulators for growth and development of these organs.
- Sciences – Thèses