Animal Molecular Breeding 2024, Vol.14, No.2, 165-177 http://animalscipublisher.com/index.php/amb 169 Another study investigated the genetic polymorphisms in pigmentation genes such as MC1R, MITF, TYR, TYRP1, and MLPHin four Chinese native rabbit breeds with different coat colors. The researchers discovered 14 genetic variants with low-to-moderate polymorphism and significant differences in gene frequency among the rabbit populations. These findings suggest that these genetic variations play a crucial role in regulating coat color in rabbits (Jia et al., 2021). 4.2 CRISPR and other genetic editing techniques The advent of CRISPR/Cas9 and other genetic editing techniques has opened new avenues for manipulating coat color in domestic rabbits. A groundbreaking study utilized the CRISPR/Cas9 system to induce mutations in the melanocortin 1 receptor (MC1R) gene, resulting in a novel pale-yellow coat color in rabbits. The researchers designed two single-guide RNAs (sgRNAs) for the MC1Rgene and confirmed the editing efficiency by injecting rabbit zygotes. The edited rabbits exhibited a loss of eumelanin synthesis, leading to the pale-yellow coat color. This study demonstrated the potential of gene editing technology to create novel phenotypes in rabbit breeding (Figure 1) (Xiao et al., 2019). In another study, researchers sequenced the MC1R gene in several domestic rabbits and identified four alleles, including two wild-type alleles and two alleles with in-frame deletions. These deletions were associated with different coat colors, such as dominant black and recessive red. The study highlighted the role of MC1R gene mutations in determining coat color and provided a foundation for further genetic editing experiments (Fontanesi et al., 2006). 4.3 Epigenetic factors influencing coat color Epigenetic modifications, such as DNA methylation, have been shown to influence coat color in domestic rabbits. A study on Rex rabbits compared genome-wide DNA methylation profiles in hair follicles between a Chinchilla group and a diluted Chinchilla group using whole-genome bisulfite sequencing (WGBS). The researchers identified 126 ,405 differentially methylated regions (DMRs) corresponding to 11,459 DMR-associated genes. These genes were primarily involved in developmental pigmentation and Wnt signaling pathways. The study provided evidence that inherited color dilution is associated with DNA methylation alterations in hair follicles, contributing to our understanding of the epigenetic regulation of rabbit pigmentation (Chen et al., 2020). Another study focused on the melanophilin (MLPH) gene, which is associated with coat color dilution in rabbits. The researchers identified two variants in the MLPH gene: an acceptor splice site variant (c.111-5C>A) and a frameshift mutation (c.585delG). They analyzed the allelic segregation and functional effects of these variants on MLPH transcript stability. The study revealed that the c.585delG variant showed perfect association with the dilution phenotype and led to a significant decrease in MLPH transcript levels in rabbits with diluted coat color. These findings provided new insights into the molecular mechanisms underlying coat color dilution. 5 Case Study: Genetic Analysis of a Specific Rabbit Population 5.1 Background and selection of the case study population The genetic basis of coat color variations in domestic rabbits (Oryctolagus cuniculus) has been a subject of extensive research due to its economic and breed characteristic importance. This case study focuses on the genetic analysis of coat color variations in a specific population of Chinese Rex rabbits. The Rex rabbit breed is known for its unique fur structure and a variety of coat colors, making it an ideal candidate for genetic studies on pigmentation. The selection of the Chinese Rex rabbit population for this case study is based on several factors. The breed exhibits a wide range of coat colors, including castor, red, blue, chinchilla, otter, and black, which provides a diverse genetic pool for analysis (Yang et al., 2015). Previous studies have identified several candidate genes associated with coat color variations in rabbits, such as MC1R, MITF, TYR, TYRP1, MLPHand ASIP, making it feasible to investigate these genes in the selected population (Utzeri et al., 2001; Fontanesi et al., 2006; Xiao et al., 2019; Chen et al., 2020; Jia et al., 2021; Zhang et al, 2023). Lastly, the economic significance of coat color in the Rex rabbit industry further justifies the selection of this population for genetic analysis (Zhang et al, 2023).
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