Animal Molecular Breeding 2024, Vol.14, No.2, 165-177 http://animalscipublisher.com/index.php/amb 166 Several genes are crucial in the pigmentation process, including the melanocortin 1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), and melanophilin (MLPH). These genes interact in complex pathways to regulate melanin synthesis and distribution. For instance, MC1Ris a critical receptor that influences the type of melanin produced by melanocytes. When activated, MC1R promotes the production of eumelanin over pheomelanin, leading to darker pigmentation (Fontanesi et al., 2006; Jia et al., 2021). MITF is a transcription factor that regulates the expression of several melanogenic enzymes, including TYR and TYRP1. TYRis the enzyme responsible for the first step in melanin synthesis, converting tyrosine to dopaquinone, which then undergoes further reactions to form either eumelanin or pheomelanin. TYRP1 assists in the stabilization and function of TYR, and mutations in these genes can lead to various pigmentation disorders (Utzeri et al., 2021; Jia et al., 2021). MLPH is involved in the transport of melanosomes, the organelles that store melanin, to the tips of melanocyte dendrites, where they are transferred to keratinocytes. Mutations in MLPHcan result in diluted coat colors due to the improper distribution of melanosomes (Fontanesi et al., 2014; Demars et al., 2018). 2.2 Key genes involved in rabbit coat color variations In domestic rabbits (Oryctolagus cuniculus), several genes have been identified as key players in determining coat color variations. These include MC1R, MITF, TYR, TYRP1, MLPH, and the agouti signaling protein (ASIP) gene. The MC1Rgene has been extensively studied in rabbits, with several alleles identified that correlate with different coat colors. For example, a 30-nucleotide in-frame deletion in MC1R is associated with red/fawn/yellow coat colors, while a 6-nucleotide in-frame deletion is linked to black coat colors (Fontanesi et al., 2006). These mutations affect the receptor's ability to bind to its ligand, leading to variations in melanin production. The TYR gene, responsible for the initial step in melanin synthesis, has also been linked to coat color variations in rabbits. Mutations in TYR can lead to albinism or other pigmentation phenotypes. For instance, specific missense mutations in TYR are associated with the albino, Himalayan, and chinchilla phenotypes in rabbits (Utzeri et al., 2021). MLPH mutations are known to cause the dilute coat color phenotype in rabbits. A frameshift mutation in the MLPHgene has been identified as the cause of the dilute (d) allele, which results in a lighter coat color due to the improper distribution of melanosomes (Fontanesi et al., 2014; Demars et al., 2018). The ASIP gene plays a role in the distribution of eumelanin and pheomelanin, with different alleles leading to various coat color patterns. For example, the wild-type allele (A) results in a light-bellied agouti phenotype, while other alleles can lead to black non-agouti or black and tan phenotypes (Yang et al., 2015; Zhang et al., 2023). 2.3 Molecular mechanisms of color expression The molecular mechanisms underlying coat color expression in rabbits involve complex interactions between various genes and their regulatory elements. These mechanisms include gene mutations, epigenetic modifications, and gene expression regulation. Mutations in key pigmentation genes can lead to changes in the structure and function of the proteins they encode, resulting in altered melanin production and distribution. For example, the frameshift mutation in the MLPH gene causes a loss of function, leading to the dilute coat color phenotype due to the improper transport of melanosomes (Fontanesi et al., 2014; Demars et al., 2018). Similarly, mutations in the MC1R gene can affect the receptor's ability to promote eumelanin production, leading to variations in coat color (Fontanesi et al., 2006). Epigenetic modifications, such as DNA methylation, also play a significant role in coat color expression. A study on Rex rabbits revealed that DNA methylation patterns in hair follicles are associated with inherited color dilution. Differentially methylated regions (DMRs) were identified between rabbits with different coat colors, suggesting that epigenetic regulation can influence pigmentation by altering gene expression (Chen et al., 2020).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==