Despite massive research efforts, the molecular etiology of bovine polledness and the developmental pathways involved in horn ontogenesis are still poorly understood. In a recent article, we provided evidence for the existence of at least two different alleles at the Polled locus and identified candidate mutations for each of them. None of these mutations was located in known coding or regulatory regions, thus adding to the complexity of understanding the molecular basis of polledness. We confirm previous results here and exhaustively identify the causative mutation for the Celtic allele (PC) and four candidate mutations for the Friesian allele (PF). We describe a previously unreported eyelash-and-eyelid phenotype associated with regular polledness, and present unique histological and gene expression data on bovine horn bud differentiation in fetuses affected by three different horn defect syndromes, as well as in wild-type controls. We propose the ectopic expression of a lincRNA in PC/p horn buds as a probable cause of horn bud agenesis. In addition, we provide evidence for an involvement of OLIG2, FOXL2 and RXFP2 in horn bud differentiation, and draw a first link between bovine, ovine and caprine Polled loci. Our results represent a first and important step in understanding the genetic pathways and key process involved in horn bud differentiation in Bovidae.

The availability of genetic tests to detect different mutations in the myostatin gene allows the identification of heterozygous animals and would warrant the superiority of these animals for slaughter performance if this superiority is confirmed. Thus, 2 mutations of this gene, Q204X and nt821, were studied in 3 French beef breeds in the program Qualvigène. This work was done with 1,114 Charolais, 1,254 Limousin, and 981 Blonde d'Aquitaine young bulls from, respectively, 48, 36, and 30 sires and slaughtered from 2004 to 2006. In addition to the usual carcass traits recorded at slaughter (e.g., carcass yield, muscle score), carcass composition was estimated by weighing internal fat and dissecting the 6th rib. The muscle characteristic traits analyzed were lipid and collagen contents, muscle fiber section area, and pH. Regarding meat quality, sensory qualities of meat samples were evaluated by a taste panel, and Warner-Bratzler shear force was measured. Deoxyribonucleic acid was extracted from the blood samples of all calves, the blood samples of 78% of the dams, and the blood or semen samples of all the sires. Genotypes were determined for 2 disruptive mutations, Q204X and nt821. Analyses were conducted by breed. The superiority of carcass traits of calves carrying one copy of the mutated allele (Q204X or nt821) over noncarrier animals was approximately +1 SD in the Charolais and Limousin breeds but was not significant in the Blonde d'Aquitaine. In the Charolais breed, for which the frequency was the greatest (7%), young bulls carrying the Q204X mutation presented a carcass with less fat, less intramuscular fat and collagen contents, and a clearer and more tender meat than those of homozygous-normal cattle. The meat of these animals also had slightly less flavor. Also in the Charolais breed, 13 of 48 sires were heterozygous. For each sire, the substitution effect of the wild allele by the mutant allele was approximately +1 SD for carcass conformation and yield, showing that the estimate of the substitution effect was independent of family structure, as it ought to be for a causal mutation. These results illustrate the challenge of using genetic tests to detect animals with the genetic potential for greater grades of carcasses and meat quality.

The objectives of the study were to evaluate allelic frequencies and to test the association of polymorphisms in the calpastatin (CAST) and µ-calpain (CAPN1) genes with meat tenderness in 3 French beef breeds. A total of 1,114 Charolais, 1,254 Limousin, and 981 Blonde d'Aquitaine purebred young bulls were genotyped for 3 SNP in the CAST gene and 4 SNP in the CAPN1 gene. Two of these markers, 1 in each gene, can be found in Australian or American commercial genetic tests. Others have previously been reported in American studies or are newly evidenced SNP. The quantitative traits studied were Warner-Bratzler shear force and a tenderness score evaluated by trained sensory panels. All the SNP were informative in the 3 breeds. Associations of individual markers or haplotypes with traits were analyzed. The results differed in the 3 breeds. The G allele of a CAST marker (position 97574679 on Btau4.0) was found to exert a significant effect on the shear force (+0.18 phenotypic SD; RSD) and tenderness score (-0.22 RSD) in the Blonde d'Aquitaine breed. In the same breed, this marker was associated with another CAST SNP (position 97576054 on Btau4.0) such that the GA haplotype appeared to be associated with tougher meat. Two CAPN1 markers (positions 45221250 and 45241089 on Btau4.0) had a significant effect on both traits in the Charolais breed (from |0.11| to |0.25| RSD). In the same breed, these markers were associated with another CAPN1 SNP (position 45219395 on Btau4.0) such that the ACA and AGG haplotypes appeared to be associated with a tender meat and a tougher meat, respectively. Consequently, the present results indicate that the effects of the markers studied are breed-specific and cannot be extended to all Bos taurus breeds. Further studies are also required to identify other more appropriate markers for French beef breeds.

BackgroundPrevious research programmes have described muscle biochemical traits and gene expression levels associated with beef tenderness. One of our results concerning the DNAJA1 gene (an Hsp40) was patented. This study aims to confirm the relationships previously identified between two gene families (heat shock proteins and energy metabolism) and beef quality.ResultsWe developed an Agilent chip with specific probes for bovine muscular genes. More than 3000 genes involved in muscle biology or meat quality were selected from genetic, proteomic or transcriptomic studies, or from scientific publications. As far as possible, several probes were used for each gene (e.g. 17 probes for DNAJA1). RNA from Longissimus thoracis muscle samples was hybridised on the chips. Muscles samples were from four groups of Charolais cattle: two groups of young bulls and two groups of steers slaughtered in two different years. Principal component analysis, simple correlation of gene expression levels with tenderness scores, and then multiple regression analysis provided the means to detect the genes within two families (heat shock proteins and energy metabolism) which were the most associated with beef tenderness. For the 25 Charolais young bulls slaughtered in year 1, expression levels of DNAJA1 and other genes of the HSP family were related to the initial or overall beef tenderness. Similarly, expression levels of genes involved in fat or energy metabolism were related with the initial or overall beef tenderness but in the year 1 and year 2 groups of young bulls only. Generally, the genes individually correlated with tenderness are not consistent across genders and years indicating the strong influence of rearing conditions on muscle characteristics related to beef quality. However, a group of HSP genes, which explained about 40% of the variability in tenderness in the group of 25 young bulls slaughtered in year 1 (considered as the reference group), was validated in the groups of 30 Charolais young bulls slaughtered in year 2, and in the 21 Charolais steers slaughtered in year 1, but not in the group of 19 steers slaughtered in year 2 which differ from the reference group by two factors (gender and year). When the first three groups of animals were analysed together, this subset of genes explained a 4-fold higher proportion of the variability in tenderness than muscle biochemical traits.ConclusionThis study underlined the relevance of the GENOTEND chip to identify markers of beef quality, mainly by confirming previous results and by detecting other genes of the heat shock family as potential markers of beef quality. However, it was not always possible to extrapolate the relevance of these markers to all animal groups which differ by several factors (such as gender or environmental conditions of production) from the initial population of reference in which these markers were identified.