Effect Of The Variation Of IGF-Ⅱ On Growth Performances And The Gene Expression Ascoiated With Muscle Development In Pigs

A paternally expressed quantitative trait locus (QTL) with major effect on muscle mass was mapped to the insulin-like growth factor 2 (IGF-Ⅱ) locus at the distal end of pig chromosome 2p. It was recently demonstrated that a G to A transition at position intron 3-nt 3072 is the quantitative trait nucleotide (QTN) underlying this QTL. The effect of IGF-Ⅱgene variation on growth performance and the expression of the genes with relation to musclar development were analysed in the poplation of Landrace and Large White and the gelded boars from Landrace×Large White cross.1. Study on the method to investigate the mutation in insulin-like growth factor gene Intron3 G3072A and the distribution of polymorphism indifferent pig breedsA mispairing PCR was used to flank the paternal expressed IGF-Ⅱgene intron3 G3072A mutation in eight breeds including Landrace (36 individuals), Large White (43 individuals), Duroc (29 individuals), Erhualian (25 individuals), Meishan (72 individuals), Wuzhishan (15 individuals), huai (15 individuals) and intercrossed Sutai (81 individuals) pigs. The results showed that the mispairing PCR is a rapid, simple and efficient method to detect single nucleotide polymorphism (SNP).The single nucleotide polymorphism(G→A transition) in IGF-Ⅱgene intron3 3072 site were significantly different between the imported populations and Chinese native populations (P＜0.01). the result of x~2 analysis showed that the distribution of three genotypes of IGF-Ⅱintron3 G3072A was very different among different breeds(x~2=260.477, P＜0.01). The result of further analysis showed that the distribution of three genotypes of IGF-Ⅱintron3 G3072A was very different among the outbred(Landrace, LargeWhite and Duroc)and the native breeds(Erhualian Meishan Wuzhishan huai)and intercrossed Sutai (x~2=251.652, P＜0.01), too.The A allele frequencies of external breeds were higher than the local breeds.GA and AA genotypes in imported populations (Landrace, Large White and Duroc pigs) reached 60%～70% and 20%～30%, respectively. Sutai pigs from Landrace×Large WhitexErhualian cross frequencies of GA genotype had reached 78%, and were the significantly highest than Chinese native populations.It implied that the A allele of IGF-Ⅱintron3 G3072A could be an important quantitative trait nucleotide (QTN) or linked to a major gene to significantly affect musclar traits in pig.2. The genetic effects of IGF-ⅡGene intron3 variance in pigsA mispairing PCR-RFLP technique was applied in this study to determine the insulin-like growth factor 2(IGF-Ⅱ) gene intron3 G3072A mutation in an outbred Landrace and Large White, and the gelded boars from Landrace×Large White cross. The difference of corresponding traits and the genetic effects between the boars inherited from parental A allele and inherited from parental G allele were analyzed. The results indicated that comparing with the boars inherited from parental G allele, the boars inherited from parental A allele increased significantly in the circumference 3.06%(P＜0.05)and index of body 3.01% (P＜0.05), respectively.The Qpat boars inherited from parental A allele had a significantly less average buttock fat thickness (15.31%, P＜0.01) ,thorax-waist fat thickness(23.74%, P＜0.01), skin thickness 9.38%(P＜0.01), fiber density (20.03%, P＜0.01); and had more less 6th～7th rib fat thickness(20.27%,P＜0.05), and had more thick shoulder fat thickness (7.97%, P＜0.05),and had higher tendemce (17.32%, P＜0.05),and had bigger the loin eye area and fiber cross-sectional area and fiber diameter than the qpat boars inherited from parental G allele. The results were suggested that the parental A allele has highly significant genetic effects in improving pig body development and carcass lean percent by increasing fiber diameter and the loin eye area, and decreasing the skin thicknes and fat percent.3. The effect of the mutation in pig IGF-ⅡGene intron3 G3072A on the developmental expression of IGF-Ⅱgene and IGF repector genesThe effect of the mutation on the development changes of IGF-Ⅱand IGF receptors mRNA expression in skeletal muscle in Large White×Landrance cross were analysed. Real- time fluorescence quantitative reverse transcription- polymerase chain reaction (FQ-RT-PCR) was employed to determine the expressions of IGF-Ⅱgene and IGF receptors and housekeeping gene GAPDH in pig muscles from Landrace×Large White cross with different genotypes of IGF-Ⅱintron3 G3072A. The results ndicated that the IGF-ⅡmRNA expression reduced gradually with growing. The IGF-ⅡmRNA expression of the Qpat inherited from parental A allele was higher than that of the qpat inherited from parental G allele at everyone ageThe experimental pigs were slaughtered at 180 days, longissimus dorsi and m.semitendinosus and m.gluteobiceps were used to analyse IGF-ⅡmRNA expression. Two-way analysis of variance was used to detect the significance of difference between Qpat and qpat in longissimus dorsi and m.semitendinosus and m.gluteobiceps,and of difference among three muscles. The epression of IGF-ⅡmRNA in m.gluteobiceps was markly higher than that in longissimus dorsi and m.semitendinosus. It was suggested that the characteristic in m.gluteobiceps was related to sports.The expression of IGF-ⅠR mRNA in longissimus dorsi and m.semitendinosus of Qpat and qpat individuals reduced gradually, but the expression of IGF-IR mRNA in longissimus dorsi of Qpat was significantly higher than that of qpat at day 90 and 120.Taking one with another, the patterns of developmental changes of expression were resemblely with that of IGF-ⅡmRNA in longissimus dorsi and m.semitendinosus, the results of partial correlation showed that there was remarkably relationship between the expression IGF-ⅡmRNA and IGF-ⅠR mRNA, but no assicated with IGF-ⅡR.4. The effect of the variation of IGF-Ⅱgene on the expression of MyoD mRNA in porcine muscleAn important economic indicator was located on lean mass traits, which were regulated by many factors in the course of muscle growth.MyoG and MyoD1 play an important role in skelenton differentiation and mature. Real- time fluorescence quantitative reverse transcription- polymerase chain reaction (FQ- RT- PCR) was employed to determine the developmental expressions of MyoG and MyoD1 and housekeeping gene GAPDH in pig muscles from Landrace×Large White cross with different genotypes of IGF-Ⅱintron3 G3072A. The results showed that Mypgenin and MyoD1 gene expression were significantly changed with age. The effect of IGF-Ⅱintron3 G3072A mutation on expression level in longissimus dorsi was not obviously ,but markedly in m.semitendinosus and m.gluteobiceps. The expression of MyoG mRNA in m.semitendinosus of Qpat individuals was remarkly higher than that of qpat at the stage of 180 day. It was sugguested that the increase of MyoG mRNA expression may promote the transform of muscle bibre types from ferment type to oxidation type. The expression pattern of MyoD1 mRNA in different muscle tissues is also different in m.semitendinosus its expression was later in an age-stage than that in longissimus dorsi during the whole development stages. The results from the present study showed that paternal A allele in IGF-Ⅱtransferred to the offspring, and then effected porcine muscle growth and development mainly through increasing MyoG expression in limb and body wall muscle tissues, in order to promote the muscle differentiation and its type transform.