The Copy Number Variations Of AHR Gene And Their Associations With Reproductive Traits In Pigs

Copy number variation (CNV) is an important form of structural variation in the genome. Studies showed that CNVs were associated with the complex diseases in humans, and also affected economic traits in domestic animals and poultry. Aryl hydrocarbon receptor (AHR) gene expressed in multiple tissues in mammals and played a key role in mediating the function of tetrachlorodibenzo-p-dioxin (TCDD), a chemical toxin, which can result in decrease of mammalian fertility. Several studies indicated that AHR gene had regulating effect on reproductive performance in pigs, and it could be used as a molecular genetic marker in pig breeding. The structure, expression and biological function of AHR gene has been extensively studied. However, associations of its copy number variation with reproductive traits in domestic species had not been reported.A total of 944 sows from four pig breeds, Duroc, Landrace, Large Yorkshire and Meishan were collected from Xingtai, Hebei, Fangshan, Beijing and Kunshan, Jiangsu, respectively, and used as experimental materials. Real-time quantitative PCR technique and 2-AACT method were used to detecting the copy number of AHR gene in the four pig breeds. As a candidate gene of reproductive traits, the association between the copy number and total number born, number born alive, litter birth weight, number weaned, length of pregnancy was analysed by fitting a general linear model (GLM) and using SAS 9.2 software package. The following main results were obtained:(1) There were two types of CNVs in porcine AHR gene, and the range of CNVs was 1-2, characterized by two types of normal (2 copies) and missing (1 copy) copy numbers. The number of sows with 2 copies and 1 copy was 78 and 94 in Duroc,169 and 90 in Landrace, 329 and 155 in Large Yorkshire, respectively. All two types existed in the three imported foreign breeds, but only normal copy number was detected in Meishan pigs.(2) Analysis of variance based on GLM showed that parity had significant effects on total number born, number born alive and litter birth weight, which increased with parity. Herd, year and season effect on the performance was significant also.(3) Association study showed that CNVs in AHR gene had significant effects in Large Yorkshire on total number born and number born alive, which were higher in sows with two copies than in sows with one copy. AHR gene copy number variations had significant effects on total number born and had nearly significant effects on number born alive in Landrace, the effect trends were the same as in Large Yorkshire. No significant CNV effect on other reproductive traits was found in the two breeds.In conclusion, There were two types of CNVs in porcine AHR gene, and the variations were significantly associated with total number born and number born alive, which could be used as a candidate genetic marker in pig breeding.