Promising Loci and Genes for Yolk and Ovary Weight in Chickens Revealed by a Genome-Wide Association Study

Because it serves as the cytoplasm of the oocyte and provides a large amount of reserves, the egg yolk has biological significance for developing embryos. The ovary and its hierarchy of follicles are the main reproductive organs responsible for yolk deposition in chickens. However, the genetic architecture underlying the yolk and ovarian follicle weights remains elusive. Here, we measured the yolk weight (YW) at 11 age points from onset of egg laying to 72 weeks of age and measured the follicle weight (FW) and ovary weight (OW) at 73 weeks as part of a comprehensive genome-wide association study (GWAS) in 1,534 F2 hens derived from reciprocal crosses between White Leghorn (WL) and Dongxiang chickens (DX). For all ages, YWs exhibited moderate single nucleotide polymorphism (SNP)-based heritability estimates (0.25–0.38), while the estimates for FW (0.16) and OW (0.20) were relatively low. Independent univariate genome-wide screens for each trait identified 12, 3, and 31 novel significant associations with YW, FW, and OW, respectively. A list of candidate genes such as ZAR1, STARD13, ACER1b, ACSBG2, and DHRS12 were identified for having a plausible function in yolk and follicle development. These genes are important to the initiation of embryogenesis, lipid transport, lipoprotein synthesis, lipid droplet promotion, and steroid hormone metabolism, respectively. Our study provides for the first time a genome-wide association (GWA) analysis for follicle and ovary weight. Identification of the promising loci as well as potential candidate genes will greatly advance our understanding of the genetic basis underlying dynamic yolk weight and ovarian follicle development and has practical significance in breeding programs for the alteration of yolk weight at different age points.

蛋黄作为卵母细胞的细胞质并提供大量储备物质，对胚胎发育具有重要生物学意义。卵巢及其卵泡层级结构是鸡体内负责蛋黄沉积的主要生殖器官。然而，蛋黄与卵巢卵泡重量的遗传调控机制仍未得到清晰阐释。本研究针对1534只由白来航鸡（White Leghorn, WL）与东乡鸡（Dongxiang chicken, DX）正反交获得的F2代蛋鸡开展全基因组关联研究（genome-wide association study, GWAS）：于产蛋起始至72周龄的11个年龄节点测定蛋黄重量（yolk weight, YW），并于73周龄时测定卵泡重量（follicle weight, FW）与卵巢重量（ovary weight, OW）。各年龄节点的蛋黄重量均表现出基于单核苷酸多态性（single nucleotide polymorphism, SNP）的中等遗传力估计值（0.25~0.38），而卵泡重量与卵巢重量的遗传力估计值相对较低，分别为0.16与0.20。针对各性状开展的独立单变量全基因组筛选，分别鉴定出12、3与31个与蛋黄重量、卵泡重量及卵巢重量相关的全新显著遗传关联位点。本研究筛选得到一批候选基因，包括ZAR1、STARD13、ACER1b、ACSBG2及DHRS12，上述基因分别在胚胎发生启动、脂质转运、脂蛋白合成、脂滴生成及类固醇激素代谢过程中发挥潜在功能。本研究首次针对卵泡重量与卵巢重量开展全基因组关联分析。鉴定到的潜在遗传位点与候选基因，将极大加深我们对动态变化的蛋黄重量及卵巢卵泡发育遗传基础的理解，并对不同年龄节点下蛋黄重量的育种改良具有重要实际应用价值。