Polymorphism in Insulin-Like Growth Factor-I ( IGF-1) and Pituitary Positive Transcription Factor-1 (Pit-1) Genes and the Effect on Growth of Indonesian Local Chicken

Abstract

Conservation in poultry genetic variation is necessary to maintain specific traits in poultry that may be utilized in the future. Morphologic measurement is one of the identification methods on genetic variation in Indonesian local chicken breeds. This study is expected to give a result on data acquisition on body weight and other morphologic character of local chicken breeds at several ages, therefore, the data can be applied to poultry selection. Local chicken growth is known to be low compared to broiler chicken. Growth is dependent on genetic and environmental factors; several genes controlling growth have been thoroughly studied. IGF-1 and Pit-1 genes are among the group of growth genes that have been recently draw attention for thorough research. Those genes play role in somatic growth, i.e., muscle, bone, epithelial and fibroblast cells. Those genes as well control production of growth and prolactin hormone. Therefore this study was designed to explore IGF-1 and Pit-1 genes in accordance with growth in Indonesia endogenous chickens. Local and broiler chickens were the object of this study which applied two steps of analyses. First, phenotypic variation by measuring morphologic characters, such as body weight, length of shank, length of beak, breast width, back width, and breast perimeter. Second, polymorphic analysis in IGF-1 and Pit-1 genes. Genotyping using PCR-RFLP - restriction enzyme Pst-1 was carried out on each individuals of local and broiler chickens. This study also attempted in correlating phenotypic and genotypic analyses. Results of this study indicated body weight and other morphologic characters of eight weeks-broiler chicken were higher than those of local chicken races (P<0.01). Among local chickens at the age of 28 weeks, pelung was the highest in morphologic characters compared to kedu, sentul, and kampong. Principal Component Analysis (PCA) on chicken morphologic characters of eight week age resulted in three clusters, i.e., broilers, pelung, and kedu, kampong and sentul. On the other hand, the analysis on 28 week aged-chickens resulted in two clusters, pelung and kedu, kampong and sentul. Similarity index of kampong was 64.70%, as it was influenced by composite index of kedu (17.70%) and sentul (17.60%). Similarity index of sentul was 71.40%, influenced by composite index of kampong 28.60 %. Kedu has similarity index of 81.20%, influenced by kampong 18.80%. Similarity index of pelung was the highest (100%), it was not dependent on composite index of other chickens. Discriminant variable on local chicken contributed significantly on back length 0.924 (canonical-1) and breast perimeter 0.870 (canonical-2), its canocial structure value was relatively high. IGF-1 gen composed three genotypes (AA, AB, and BB) in broiler chickens, while that of local chickens was two genotypes (AA and AB). Body weight in all races of chickens at entire ages with AA genotypes was lower compared to chickens with AB genotypes. Body weight of sentul, kedu, and kampong at the ages of one to five months was not significantly different, in spite of the two different genotypes (AA and AB). Back length and breast perimeter of pelung ((P<0.05) were higher compared to sentul, kedu, and kampong, regardless genotyping (AA and AB). . Pit-1 gene in exon 6 resulted very low in nucleotide polymorphism. There was only one nucleotide differed out of 179 nucleotides, the other 178 nucleotides was conserved. Reconstruction of phylogenetic tree strengtened the result that only sentul chickens (SN606 and SN632) located in a separate cluster of other races. However, sentul was in the same cluster if domesticated goose (Anser anser) put as an outgroup in the phylogenetic tree analysis. Pit-1 gene in intron-2 alignment denoted that therein 374 nucleotides were conserve, while 13 nucleotides varied. Reconstruction of phylogenetic tree based on this gene showed that there was no clear relationship between nucleotide variation in intron-2 of Pit-1 gene and body weight as well as the genotype. IGF-1 genetic marker successfully discriminated the genotypes in consideration with body weight in both local and broiler chickens. However, Pit-1 genetic marker was not able to discriminate characters clustering.