Genetic Variability Of Growth Hormone (GH) And Leptin (LEP) Genes And Their Association With Growth Traits In Sheep Breeds Of Tamil Nadu
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Date
2014
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Tamil Nadu Veterinary and Animal Sciences University
Abstract
The present study was undertaken to characterize GH and LEP genes,
genes affecting growth traits and regulation of body weight and to associate their
polymorphism with growth traits in sheep breeds of Tamil Nadu. To characterize
these genes in all the eight sheep breeds of Tamil Nadu, four sets of primers to
amplify the whole GH gene (1-2162 bp) and six sets of primers to amplify the
Exon 2 (172 bp) and Exon 3 (2731 bp) of LEP gene were designed and the
sequences were compared with reference sequences from NCBI. Three SNPs 480
G>A (SNP-G1), 871 G>A (SNP-G2) and 1259 A>C (SNP-G3) were identified in
Intron 1, Intron 2 and Intron 3 of GH gene respectively. SNP-G1 was seen in all the eight
breeds, SNP-G2 in Nilagiri and SNP-G3 in Madras Red and Ramnad White
breeds of sheep.
In LEP gene, Intron 1 at 13774 bp a ‘GTT’ segment which was present in
two copies in the reference sequence was found as a single copy in Tamil Nadu
breeds. The SNPs identified in LEP gene were 13893 T>C (SNP-L1) in
Intron 1, 14013 C>T (SNP-L2) in Exon 2 and 14074 A>G (SNP-L3) and 14090
G>A (SNP-L4) in Intron 2. In Exon 3, 16973 G>A (SNP-L5), 17476 C>T
(SNP-L6) and 18082 G>A (SNP-L7) were identified.
The identified SNPs which showed heterozygosity and present in Madras
Red, Mecheri or Nilagiri breeds were genotyped. The SNPs of GH gene were
genotyped using tetra-primer ARMS-PCR and the SNPs in LEP gene were
genotyped using restriction enzymes (BsrD1 and HinP1I).
Using the least-squares analysis of variance, it was found that the SNP-G1
was associated significantly with weaning weight and pre-weaning ADG. Of the
three genotypes, the AA genotype had a higher weaning weight of 13.49 ± 1.15 kg
and pre-weaning ADG of 120.89 ± 10.76 g. For the SNP-L6, the CC genotype
was associated significantly with higher post-weaning ADG of 46.88 ± 2.28 g in
Nilagiri sheep. The animals with A allele performed consistently better in all age
groups and haplotypes AA*CC or AA*CT showed better growth traits and ADG
at all ages. Therefore, A allele, and AA*CC, AA*CT haplotypes could be
considered as potential genetic markers in Nilagiri breed.
Analysis of the promoter region of GH and LEP genes in-silico revealed
six binding sites for transcription factors in ~ 940 bp upstream of GH gene and
~ 2500 bp analysis of the LEP promoter region revealed nine binding sites for
C/EBP and one SP1 binding site as compared with the human and bovine
promoter regions of GH and LEP genes respectively.
In the present study, eight novel SNPs were identified in both GH and LEP
genes. Of these SNPs, SNP-G1 and SNP-G3 are characteristics of indigenous
sheep; SNP-G2 and SNP-L6 are breed specific in Nilagiri breed and SNP-L2 is
breed specific in Tiruchy black sheep.
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Keywords
Single Nucleotide Polymorphism, Leptin, Growth Hormone