Genetic Effect Of Haplotypes In The Promoter Region Of Porcine Myostatin Gene

Myostatin is a negative regulator of skeletal muscle mass. It plays a pivotal role in controlling skeletal muscle mass in mammals. Polymorphisms in its promoter region likely impact transcription and production traits. In this study, eight haplotype constructs involving three polymorphic sites in the promoter region of porcine myostatin gene, namely 435, 447 and 879, were obtained using site directed mutagenesis method, and their effect on gene expression was analyzed in vitro by transient transfection of the individual reporter constructs into C2C12 cells. Castrated full-sibling Lulai pigs with the same days of age (30) were used to compare the differences of myostatin mRNA expression between BC and CC genotype in longissimus dorsi (LD), semimembranosus (SM), semitendinosus (ST) muscles using quantitative RT-PCR (qRT-PCR) with GAPDH as internal standard. Furthermore, the effect of haplotypes on MyHCs expression and muscle fiber diamer and density were studied using qRT-PCR and paraffin section respectively. The selection of haplotypes will be helpful for increasing body weight and related traits in pigs. The results are summarized as follows:1. Eight vectors were constructd. Four of the eight constructs habor the identified haplotypes, namely pGL3-A, pGL3-B, pGL3-C and pGL3-D, and the remainings are hypothetical ones. Moreover, C and D haplotypes were first identified in our laboratory.2. In vitro study indicated that the activity of pGL3-A in driving reporter gene transcription is significantly higher than other seven constructs (P < 0.01). Among the four haplotypes identified in pig populations, pGL3-A has the highest activity and pGL3-D has the lowest activity. The activity of pGL3-C is higher than pGL3-B and pGL3-D, but lower than pGL3-A. In vivo study indicated that as compared to CC animals, the myostatin mRNA level of BC animals is relatively lower in both SM and ST skeletal muscles, and the difference was significant in the SM muscle (P < 0.01). B haplotype has a positive effect on muscle growth. 3. Moreover, in the three skeletal muscles including LD, SM and ST muscles, the mRNA levels of MyHC I, MyHC IIa, MyHC IIb and MyHC IIx were higher in genotype BC than CC. Furthermore, the muscle fiber diameter and density were also compared between BC and CC animals, although the difference was not significant (P > 0.05). It is likely that MyHCs expression and skeletal muscle traits are affected by other genetic and nutritional factors.