-Previously, we have shown that alleles of the BM1500 microsatellite, located 3.6 kb downstream of the leptin gene in cattle, were associated with carcass fat measures in a population of 154 unrelated beef bulls. Subsequently, a cytosine (C) to thymine (T) transition that encoded an amino acid change of an arginine to a cysteine was identified in exon 2 of the leptin gene. A PCR-RFLP was designed and allele frequencies in four beef breeds were correlated with levels of carcass fat. The T allele was associated with fatter carcasses and the C allele with leaner carcasses. The frequencies of the SNP alleles among breeds indicated that British breeds have a higher frequency of the T allele whereas the continental breeds have a higher occurrence of the C allele. A ribonuclease protection assay was developed to quantify leptin mRNA in a separate group of animals selected by genotype. Animals homozygous for thymine expressed higher levels of leptin mRNA. This may suggest that the T allele, which adds an extra cysteine to the protein, imparts a partial loss of biological function and hence could be the causative mutation.leptin / cattle / obese / fat / marbling
Previously, we have shown that alleles of the BM1500 microsatellite, located 3.6 kb downstream of the leptin gene in cattle, were associated with carcass fat measures in a population of 154 unrelated beef bulls. Subsequently, a cytosine (C) to thymine (T) transition that encoded an amino acid change of an arginine to a cysteine was identified in exon 2 of the leptin gene. A PCR-RFLP was designed and allele frequencies in four beef breeds were correlated with levels of carcass fat. The T allele was associated with fatter carcasses and the C allele with leaner carcasses. The frequencies of the SNP alleles among breeds indicated that British breeds have a higher frequency of the T allele whereas the continental breeds have a higher occurrence of the C allele. A ribonuclease protection assay was developed to quantify leptin mRNA in a separate group of animals selected by genotype. Animals homozygous for thymine expressed higher levels of leptin mRNA. This may suggest that the T allele, which adds an extra cysteine to the protein, imparts a partial loss of biological function and hence could be the causative mutation.
The Roan locus is responsible for the coat coloration of Belgian Blue and Shorthorn cattle. The solid-colored and white animals are homozygotes, and the roan animals, with intermingled colored and white hairs, are heterozygous. The roan phenotype was mapped to cattle Chromosome (Chr) 5 with microsatellites, and a candidate gene was proposed (Charlier et al. Mamm Genome 7, 138, 1996). PCR primers to the exons of this candidate gene, the steel locus or mast cell growth factor (MGF) were designed. Solid-colored and white animals were sequenced. A missense mutation at 654 bp (amino acid 193, Ala --> Asp) was detected in these two groups. A PCR-RFLP was designed to this single base pair change, and 143 animals in total (Belgian Blue, Shorthorn, and various other breeds) were screened. In addition, the Canadian Beef Cattle Reference Herd (http://skyway. usask.ca/ approximately schmutz) was used to verify Mendelian inheritance of this marker with the phenotypic inheritance of roan. Our data suggest that this mutation in the bovine MGF gene is responsible for the roan phenotype.
A single nucleotide polymorphism (SNP) in the corticotrophin-releasing hormone gene (CRH C22G) alters the fourth amino acid in the signal sequence from proline to arginine. Two other SNPs (CRH A145G and C240G) occur in the propeptide region at residue positions 45 and 77, respectively, that result in serine/asparagine and histidine/aspartic acid substitutions respectively. These SNPs, as well as SNPs in pro-opiomelancortin (POMC), leptin (LEP) and melanocortin-4 receptor (MC4R), were evaluated for associations with average daily gain, end-of-test rib-eye area, shipping weight and hot carcass weight in a group of 256 steers using a general linear model. The CRH C22G SNP was associated with end-of-test rib-eye area (P < 0.034) and hot carcass weight (P < 0.0015). The SNP in POMC was associated with shipping weight (P < 0.0078) and hot carcass weight (P = 0.006) while it approached significance for average daily gain (P < 0.07). The SNP in MC4R approached significance for hot carcass weight (P < 0.085) while no significance was observed between the leptin SNP and the above listed traits. Because both CRH and POMC regulate appetite, potential interaction effects between these two genes were assessed. The absence of an interaction effect between CRH and POMC with hot carcass weight suggests that these genes act independently to increase carcass yield. These gene effects used singularly or together could result in an economic benefit to the beef industry.
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