Haplotype Diversity In Myostatin Promoter Region And Its Associations With Birth Weight And Growth Traits In Pigs

Myostatin plays a critical role by negatively regulating skeletal muscle mass in mammals. Although some natural mutations were proved to be responsible for hypermuscular traits in cattle, sheep, dog as well as in human, no missense mutation causing differences in skeletal musclular traits was identified in pigs. The present study examined simutaneouly the three polymorphic sites of 5′regulatory region, i.e. 435 G/A, 447 G/A and 879 T/A, in porcine myostatin gene, identified and characterized four haplotypes in six pig breeds, and analyzed their associations with Duroc and Yorkshire birth weight and early growth traits. The results are as follows:1. All of the three SNPs were identified in the amplified fragment of 706 bp in porcine myostatin promoter region. Altogether, 521 Duroc, 432 Yorkshire, 148 Landrace, 32 Laiwu and 33 Dapulian pigs were genotyped for the three SNPs. For 435 A/G SNP, allele A was less frequent in Duroc than in other four populations. For 447 G/A SNP, allele A was less frequent in Yorkshire and Landrace than in other three populations. For 879 A/T SNP, allele A was less frequent in Duroc, Yorkshire and Landrace than in other three populations. All SNPs in the five pig populations were in Hardy-Weinberg equlibrium (P>0.05). All of the three SNPs were in linkage disequilibrium (P<0.05), except for the SNPs 435 and 447 in Laiwu and Dapulian populations.2. Analysis with PHASE v2.0 revealed three haplotypes at myostatin promoter positions 435, 447 and 879 (H1, A-G-T; H2, G-A-T and H3, A-A-A) in the above five pig populations. Haplotype H2 was prevalent in Duroc population, haplotype H1 was prevalent in both Yorkshire and Landrace populations and haplotype H3 was prevalent in both Laiwu and Dapulian populations. Another haplotype of H4(A-A-T) was only found in wild boars. Of the nine wild boars investigated, seven were diplotype H3H3, one was diplotype H2H3 and one was diplotype H3H4.This study, for the first time, revealed a novel haplotype A-A at 445 and 447 in Duroc and Yorkshire pigs, respectively; although the haplotype frequency is much lower compared to that occurred in Laiwu and Dapulian pigs, indicating that these two sites were not in complete disequlibrium.Comparison of the four haplotypes revealed that only one nucleotide difference existed between H4 and the other three haplotypes. The phylogenetic relationship among the four haplotypes infered with neighbor-joining method of MEGA 4.0 indicated that haplotype H4 was more ancestral and the other three haplotypes H1, H2 and H3 were derived from haplotype H4.3. For the three SNPs at positions 435, 447 and 879, their associations with birth weight and early growth traits including birth weight at day 21 (BW21) and day 70 (BW70) as well as daily gain from birth to day 21 (ADG1) and from day 21 to day 70 (ADG2) were analyzed in Duroc and Yorkshire pigs, respectively.SNP 435 A/G: In Yorkshire pigs, the effects of genotype on birth weight and early growth traits were not significant (P>0.1). In Duroc pigs, the effects of genotype on birth weight and some of the early growth traits (BW70 and ADG2) were not significant (P>0.5), however, was nearly significant (P=0.0531) on BW21 and ADG1, respectively.SNP 447 G/A: In both Duroc and Yorkshire pigs, the effects of genotype on birth weight and early growth traits were not significant (P>0.1). SNP 879 T/A: The genotype effects on BW21 and ADG1 were significant in Duroc and Yorkshire pigs (P<0.05), however, the effects were related to pig breed: In Duroc, genotype TA had higher body weight at day 21 and higher average daily gain from birth to day 21; in Yorkshire genotype TT was higher than TA for the same two traits. Its effects on ADG2 were different: in Duroc pigs, genotype TT had significantly higher average daily gain from day 21 to day 70 (P<0.001).In Duroc, haplotypes of the three SNPs were associated with BW21, ADG1 and ADG2 (P<0.05). Diplotype H2H3 had significantly higher BW21 and ADG1, but significantly lower ADG2 than diplotype H1H1. Therefore, in pig breeding or production using Duroc, selecting H1H1 individuals is expected to increase growth rate.