Structure And Polymorphism Of Interleukin-2 Gene In Chicken

Chicken interleukin 2 (chIL-2), a primary cytokine excreted mainly by activated T cells, can significantly enhance immunity. The chIL-2 has been proven to play an important role not only in host response to coccidiosis and salmonella among parasite and bacterial diseases but also in host's enhanced immune responses to vaccines. This study was carried out to examine the genetic polymorphisms and their potential impact on the structure and function on chIL-2.The present study generated the chIL-2 complete genomic DNA sequences of six birds from Cambodia (2), Egypt (1), Laos (1) and Uganda (2), and also partial intron 2 DNA sequences of 66 chickens from Cambodia, Egypt, Laos, Uganda, Fiji as well as Jingning, Huining and Wuwei populations of Gansu province of China using microsatellite genotyping, and direct as well as cloning sequencing methods. The raw sequencing data was manually edited using the Chromas software, and aligned for comparison using the MEGA 3.0 program and for genetic polymorphism analysis using the DnaSP 4.0 software. The established haplotypes were used to reconstruct their network relationships with the Network 4.0 software.The results showed that the six complete genomic DNA sequences carried 12 insertion/deletion sites and 65 SNPs (including 41 transitions and 24 transversions), of which five SNPs were located within the coding region and four were non-synonymous mutations leading to four amino acid replacements. Microsatellite genotyping of a 175 bp long fragment indicated that there were 12 and 13 poly-As in the X10 heterozygous sample of Laos based on the comparison against the Egypt sample with a known sequence carrying 10 poly-As. There were 17 haplotypes identified from 103 sequences of the 66 individuals, of which 15 were novel. The network relationships of the 17 haplotypes consisted of three clades: A clade had a start like pattern, indicating that it probably experienced a recent and rapid expansion associated with domestication with the H4 or H11 as a putative ancestral haplotype; a single haplotype of H17 belonged to B clade; high frequency of sequences in the C clade showing no expansion signature indicated its origin associated with commercial chicken genetic background.