Polymorphism Of Four Growth And Development Candidate Genes In Dezhou Donkey And Their Association With Body Size Traits

Donkey husbandry is a characteristic animal husbandry industry in China.In recent years,donkey farming has developed rapidly with the increasing demand for e-jiao and other products.However,an important problem is that the traditional donkey raising is mainly used for draft,while the current donkey raising industry is aimed at meat,skin and milk,so there is a lack of specialized superior breeds.Dezhou donkey is one of the large and fine donkey breeds in China,which belongs to the important livestock and poultry genetic resources,and is also an important animal breed for the development of donkey industry.The growth and development indexes are important economic traits,and the amount of meat and milk produced are related to the growth and development of donkey.Therefore,it is of great significance to study the genetic basis of donkey growth and development traits,which will lay a theoretical foundation for molecular breeding of specialized donkey breeds.In this study,insulin like growth factor-1 and-2(IGF1 and IGF2),and long-chain fatty acid coenzyme A synthase 1 and 3(ACSL1 and ACSL3)were chosen as candidate genes for growth and development traits.Firstly,the expression levels of these genes in different periods and different tissues of Dezhou donkey were investigated,and a total of 13 mutation loci were screened and identified on the candidate genes.Then,the population genetic parameters of polymorphic sites and their relationship with the growth and development traits of Dezhou donkeys were analyzed.The results of this study are as follows:1. The expression level analysis of IGF1,IGF2,ACSL1 and ACSL3 genes in different tissues of Dezhou donkey with various age showed that in the heart,liver,spleen,lung,renal and gastric tissues,the expression of IGF1 gene in adult donkeys was significantly higher than that in young donkeys;the IGF2 gene was higher in all seven tissues of the young donkey than that in the adult donkey.The expression levels of IGF1 and IGF2 genes in the muscle tissues of young and adult Dezhou donkeys were also consistent with the previously reported result(declines with age).Expression levels of IGF1 and IGF2 genes in different tissues of young and adult Dezhou donkeys are consistent with the mechanism that IGF1 gene plays a role after birth and IGF2 gene functions during the period of embryo.Therefore,IGF1 and IGF2 gene can promote the growth and development of Dezhou donkeys.The expression of ACSL1 gene in 7 tissues of adult donkey is higher than that of young donkey;ACSL3 gene is higher in heart,liver,spleen,lung,renal and gastric tissues of adult donkey than in young donkeys,while in muscle tissue the expression of young donkeys is higher.The regular expression of ACSL1 and ACSL3 genes in the tissues of Dezhou donkeys are similar to other animals.2. IGF1-1(g.A703862G)and IGF1-2(g.A764500G)mutation sites were detected in IGF1(NW?014638758.1)intron of Dezhou donkey;IGF2-1(g.G281766A)and IG F2-2(g.C291322T)mutation sites were detected in IGF2(NW?014638551.1)intron;F our indels were detected in ACSL1(NW?014637410.1)gene including ACSL1-1(g.3414448-3414447),ACSL1-2(g.3408868-3408867),ACSL1-3(g.3407870-3407863),and AC SL1-4(g.3391562-3391556);Five indels were detected in ACSL3(NW?014637842.1)g ene including ACSL3-1(g.859009-859005),ACSL3-2(g.853260-853259),ACSL3-3(g.852141-852137),ACSL3-4(g.850942-850941)and ACSL3-5(g.842395-842394).3. Analysis results of linkage disequilibrium of IGF1,IGF2,ACSL1 and ACSL3 genes showed that there is no linkage relationship between the polymorphic loci of IGF1genes in Dezhou donkeys.The two polymorphic loci of the IGF2 gene are strongly linked in the female and male donkeys,and the values of r~2are 0.871 and 0.888,respectively.In the ACSL1 gene,there is a strong linkage between ACSL1-1 and ACSL1-3 loci in female donkey populations(r~2=0.49),while ACSL1-3 is linked with ACSL1-1 and ACSL1-4 loci in male donkeys,respectively(r~2=0.59 and 0.34).The maximum r~2values between the ACSL3-2 and ACSL3-5 loci in the ACSL3 gene in female donkeys and male donkeys are0.82 and 0.84,implying the strong linkage disequilibrium between polymorphic loci.The strong linkage relationships were found between ACSL3-1 and ACSL3-2,ACSL3-1 and ACSL3-3,ACSL3-2 and ACSL3-4,ACSL3-4 and ACSL3-5 among female and male donkey populations(r~2>0.33).Haplotypes with frequencies greater than 0.05 were also constructed based on all mutation sites,and the analysis results were found to be consistent in both female and male population of Dezhou donkey.4. Association analysis between the genotypes and growth traits at 13 polymorphic loci showed that there was a significant association between the polymorphic loci of IGF1,IGF2,ACSL1,and ACSL3 genes and the growth traits of Dezhou donkeys(P<0.05).Specifically,the genotype GG(IGF1-1 and IGF1-2),GG(IGF2-1),CC(IGF2-2),DD(ACSL1-1),II(ACSL1-2),II(ACSL1-3),DD(ACSL3-1),II(ACSL3-2),DD(ACSL3-3),and II(ACSL3-3)individuals showed higher growth traits in Dezhou donkeys.In the haplotype combination analysis,the haplotype combination of female and male donkeys IGF1:Hap1Hap1(GG-GG),ACSL1:Hap6Hap6(DD-II-II-II),ACSL3:Hap5Hap5(DD-II-DD-II-II),female donkey IGF2:Hap1Hap1(GG-CC)and male donkey IGF2:Hap2Hap2(AA-TT)showed higher growth performance.The above analysis results show that the association analysis results of genotype and haplotype combinations with the growth traits of Dezhou donkeys are basically the same,which also proved the reliability of the two results.