Insulin like Growth Factor-1 (also called IGF-1 or somatomedin C), is a highly conserved molecule similar to the molecular structure of insulin. It is made up of 70 amino acids encoded by the IGF1 gene. IGF-1 has many effects on the body. It plays a key role in the control of skeletal characteristics, metabolism, and growth of adipose tissue and deposition of fat in chickens. IGF1 promotes cell division and cell growth in the body. It also plays a role in cellular repair in the brain, heart and muscles of the animal. The perturbation of IGF1 can cause many consequences to the animal. IGF-1 is a major mediator of the effects of growth hormone (GH) produced in the pituitary gland, then released into the blood stream, later triggers the liver to produce IGF-1. Few studies have shown no direct correlation between GH levels and the growth rate in chickens; hence this has led to study IGFs as mediators of the functions of GH.
The action of mechanism is initiated by binding of IGF1 to its receptor called IGF1 receptor which is present in many cell types in many tissues. This mediates intracellular many cellular signal transductions at the molecular level. The mechanisms of involvement of these proteins in insulin/IGF signaling pathways are largely speculative and require further study. The IGF1 produced in the muscle offers main benefits to the gain of the muscle. They trigger different protein activities involved in the muscle protein synthesis. There are multiple factors associated with the production of IGF1, such as low levels of glucose or deficiency of protein can trigger a significant decline of the IGF1, vice versa.
Endocrinology in birds has always been an unfamiliar subject to the researchers, even though endocrinopathy in birds have high occurrence. Hormones such as the growth hormone, IGF, thyroid hormones and insulin, play important and diverse roles in animal growth. Very few information is available that explains the nutrient-IGF relationship in the poultry industry. However,
IGF1 have been sensitive to the alteration in the nutrition in domestic fowl. Studies performed by two separate groups show food deprivation for 5 day depresses circulating IGF1 concentration and upon re-feeding, concentration return to near initial concentration. Other studies in contrast, reported that a complete return to normal IGF1 was observed following depriving from feeding, suggesting that the extent of nutrient deprivation determines the rate at which IGF1 synthesis and secretion return to normal following periods of nutrient modification. The study led by Del Vesco and its colleagues in 2013, has evaluated the effects of different dietary methionine levels on IGF1 and GH gene expression in liver and muscle tissues. The IGF1 and GH gene expression in muscle tissues was not affected by methionine supplementation. However, IGF1 gene expression in the liver was higher in broilers fed methionine diet. They further demonstrated the effect of heat stress and supplementation of methionine on the GH and IGF1gene expression in the liver and found that methionine supplementation increased IGF1 and GH expression. They observed that the highest GHR expression occurred at normal temperature and not at heat stress in supplementation of methionine in the diet. This suggests that the protein degradation is induced by the heat stress, but supplementation of methionine triggers protein deposition because it increases the expression of gene related protein synthesis and reduces the expression of genes related to protein catabolism.
JaromirKadlec along with other workers has found IGF1 as a potential candidate gene responsible for various metabolic traits in chickens. They have identified single variable gene known as single nucleotide polymorphism (SNP) in total 132 birds using molecular techniques and have correlated the genotype frequencies with growth and fat deposition in chickens. The results depict identical IGF1 amino acid sequences among chickens, rats and human peptides.
In spite of the wealth of knowledge that has accumulated concerning IGF1 in the past few decades, still many details of IGF1 in broilers remain to be clarified about the role of different pathways.