Molecular cloning, sequence characteristics, and polymorphism analyses of the tyrosinase-related protein 2 / DOPAchrome tautomerase gene of black-boned sheep (Ovis aries)

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Abstract:

Tyrosinase-related protein 2 (TYRP2) plays a pivotal role in the biosynthesis of eumelanin. Black-boned sheep have excessive melanin and eumelanin, resulting in dark (black) muscles and organs. This study was designed to investigate the effects of variants of the TYRP2 gene on black traits and coat colour of black-boned sheep. Melanin traits were measured in three populations of sheep (Nanping black-boned, Nanping normal, and Romney Marsh) and compared in this study. From the TYRP2 cDNA, all 8 exons and their flanking regions were amplified and characterized. Fifteen single nucleotide polymorphisms (SNPs) were identified in the exons and their flanking regions. Five exonic polymorphic sites, including two synonymous (c.93T>G and c.1140C>T) and three non-synonymous mutations (c.163C>T (p.R55W), c.605G>A (p.R202H), and c.1141A>G (p.T381A)), were retrieved. PCR-RFLP analysis of c.605G>A showed that the frequencies of allele G in the Nanping black-boned, Nanping normal, and Romney Marsh sheep were 0.632, 0.603, and 0.886, respectively. Sheep with the GG genotype had significantly (P < 0.05) lower tyrosinase activity, alkali-soluble melanin content, and ratio of eumelanin : total melanin than sheep with GA and AA genotypes when measured across all investigated samples but not when samples within each population of sheep were compared. However, there was no association of TYRP2 genotype at a single SNP position with coat colour across populations. Nonetheless, the two breeds with higher overall tyrosinase activity did produce darker and more varied coat colours than the breed with lower tyrosinase activity.

La protéine 2 apparentée à la tyrosinase (TYRP2) joue un rôle important dans la biosynthèse de l’eumélanine. Les moutons à chair noire ont des quantités excessives de mélanine et d’eumélanine ce qui leur confère des muscles et des organes foncés (noirs). Cette étude a été conçue pour investiguer les effets de différents variants du gène TYRP2 sur les caractères noirs et la couleur du pelage chez les moutons à chair noire. Dans ce travail, les caractères affectés par la mélanine ont été mesurés et comparés chez trois populations du mouton (Nanping black-boned, Nanping normal et Romney Marsh). L’ADNc, les huit exons et les régions bordantes du gène TYRP2 ont été amplifiés et caractérisés. Quinze SNP ont été identifiés au sein des exons et des régions bordantes. Cinq sites polymorphes dans les exons, deux mutations synonymes (c.93T>G et c.1140C>T) et trois non-synonymes (c.163C>T (p.R55W), c.605G>A (p.R202H) et c.1141A>G (p.T381A)), ont été relevés. Par analyse PCR-RFLP du polymorphisme c.605G>A, il a été montré que les fréquences de l’allèle G au sein des populations Nanping black-boned, Nanping normal et Romney Marsh étaient respectivement 0,632, 0,603 et 0,886. Les moutons de génotype GG affichaient une activité tyrosinase, une teneur en mélanine soluble en conditions alcalines et un ratio eumélanine : mélanine totale significativement (P < 0,05) plus faibles que chez les moutons de génotype GA ou AA lorsque les mesures comparées étaient prises sur l’ensemble des animaux mais pas au sein de chaque population. Cependant, aucune association n’a été observée entre le génotype de TYRP2 à une seule position SNP et la couleur du pelage chez ces populations. Néanmoins, les deux races avec une activité tyrosinase globalement plus élevée présentaient des pelages plus foncés et plus variés que la race à faible activité tyrosinase.

Document Type: Research Article

Publication date: December 1, 2009

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  • From its inception in 1957, this international cytogenetics journal has catered to the research areas of the members of the Genetics Society of Canada; traditionally, these have included agriculture, entomology, genetics/cytogenetics, and evolutionary mechanisms. The contents of the journal have evolved as contributors developed new technologies and interests. A 20-member Editorial Board is composed of scientists from around the world. Reviews and commentary from respected experts are often featured.
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