SNPs In5’ Regulatory Region Of Chicken MTNR1A Gene And Their Association With Laying Trait

Melatonin (Mel) is an important hormonal signal in the coordination of the lighting andthe reproductive system. It effects on the specific receptors which distribute in thehypothalamus-pituitary-gonadal axis to regulate the reproductive function. However, itremains unknown that how these receptors participate in the reproductive regulation. Thepresent study aims at investigating the single nucleotide polymorphisms in the5’ regulatoryregion of chicken MTNR1A gene and verifying the differences between the transcriptionalactivities of the different haplotypes in molecular level.Taking the Shouguang and Wenchang chickens as the subjects, the5’ regulatory regionswere amplified, and the SNPs were detected by cloning sequencing and direct sequencing,and then the laying traits were associated with them, and then three haplotypes that had stronglinkage disequilibrium were constructed to do dual luciferase reporter assays. The resultssuggested that:(1) In the eight SNPs of Shouguang chickens, the loci-100,-110,-126,-329hadsignificant association with the age at first egg and the egg production during20~25wks ofage, and the main effect of MTNR1A gene was additive, while the dominant effect was notsignificant. At the locus-100, chickens with TT genotype were4.5d earlier than those withGG genotype in the age at first egg, while the egg production during20~25wks of age was2.3more. The chickens with alle T were2.3d earlier than those with G in the age at first egg,and1.2more in the egg production during20~25wks of age. The results of-110were thesame as those of-100. At the locus-126, chickens with CC genotype had earlier ages thanthose with CT and TT genotype. The chickens with alle C were2.2d earlier than those of T inthe age at first egg, and1.2more in the egg production during20~25wks of age. At the locus-329, chickens with CC genotype were4.1d earlier than those with AA genotype at the age atfirst egg, and2.2eggs more during20~25wks of age. The chickens with alle C were2.1d earlier than those with A in the age at first egg, and1.1more in the egg production during20~25wks of age. Nevertheless, at the locus-538, the SNP only had significant associationwith the age at first egg, and chickens with TT genotype were earlier than those with GGgenotype. All the eight SNPs had no significant association with the total egg production andthe egg production during26~45and46~50wks of age;(2) In the ten SNPs of Wenchang chickens, the SNP of-134had significantassociation with the total egg production and the egg production during26~37and38~46wksof age. The SNP of-538had significant association with the egg production during20~25wks of age, while the other SNPs had no significant association with the laying trait;(3) The results of linkage disequilibrium tests showed that the three loci of-100,-110and-126closely linked together, and three haplotypes (TTT, CTT and TCG) and sixdipoltypes were constructed. Hens with CTT had earlier age at first egg by2.6d and1.4eggsmore during20~25wks of age (P<0.01), compared with those haplotype TCG. Hens withTTT also had earlier age at first egg and more eggs during20~25wks of age, which didn’treach the statistical significant level. The haplotype CTT and TTT had a significantinteraction effect which delayed the age at first egg and decreased the egg production;(4) Three haplotypes TTT, TCG, CTT were constructed and transfected into chickenthecal cells in vitro to verify the transcriptional efficiency differences. Luciferase reporterassays showed that the transcriptional efficiency of CTT was significantly higher than that ofTTT, TCG.In conclusion, the5’ regulatory region of MTNR1A gene are highly polymorphic andsome candidate molecular markers were detected, which helps to understand the mechanismthat melatonin receptors mediate the reproductive function of melatonin and provide datareference for the genetic improvement of local chicken.