[Show abstract][Hide abstract] ABSTRACT: Texel sheep are renowned for their exceptional meatiness. To identify the genes underlying this economically important feature, we performed a whole-genome scan in a Romanov x Texel F2 population. We mapped a quantitative trait locus with a major effect on muscle mass to chromosome 2 and subsequently fine-mapped it to a chromosome interval encompassing the myostatin (GDF8) gene. We herein demonstrate that the GDF8 allele of Texel sheep is characterized by a G to A transition in the 3' UTR that creates a target site for mir1 and mir206, microRNAs (miRNAs) that are highly expressed in skeletal muscle. This causes translational inhibition of the myostatin gene and hence contributes to the muscular hypertrophy of Texel sheep. Analysis of SNP databases for humans and mice demonstrates that mutations creating or destroying putative miRNA target sites are abundant and might be important effectors of phenotypic variation.
[Show abstract][Hide abstract] ABSTRACT: Studying the muscular hypertrophy of Texel sheep by forward genetics, we have identified an A-to-G transition in the 3'UTR of the GDF8 gene that reveals an illegitimate target site for microRNAs miR-1 and miR-206 that are highly expressed in skeletal muscle. This causes the down-regulation of this muscle-specific chalone and hence contributes to the muscular hypertrophy of Texel sheep. We demonstrate that polymorphisms which alter the content of putative miRNA target sites are common in human and mice, and provide evidence that both conserved and nonconserved target sites are selectively constrained. We speculate that these polymorphisms might be important mediators of phenotypic variation including disease. To facilitate studies along those lines, we have constructed a database (www.patrocles.org) listing putative polymorphic microRNA-target interactions.
Full-text · Article · Feb 2006 · Cold Spring Harbor Symposia on Quantitative Biology
[Show abstract][Hide abstract] ABSTRACT: A QTL for muscle hypertrophy has been identified in the Belgian Texel breed. A population of F2 and backcross lambs created from crosses of Belgian Texel rams with Romanov ewes was studied. Effects on carcass traits and muscle development of the Belgian Texel breed polygenes and Belgian Texel single QTL were compared. In both cases, carcass conformation and muscularity were improved. The Texel polygenic environment improved conformation mainly through changes in skeletal frame shape. Segments were shorter and bone weight lower. Muscles were more compact, shorter, and thicker. The single QTL affected muscle development. Thickness and weight of muscles were increased. Composition in myosin changed toward an increase of fast contractile type. The relative contribution of hind limb joint to carcass weight was increased. Differences in skeletal frame morphology among the three genotypes of the single QTL were small. Conformation scoring was mainly influenced by leg muscularity. Back and shoulder muscle development, which largely contributed to variability of muscularity, were less involved in the conformation scoring. Lastly, the QTL explains a small part of differences between these Belgian Texel and Romanov breeds for conformation or muscle development. A large part of genetic variability remains to be explored.
No preview · Article · Dec 2004 · Journal of Animal Science
[Show abstract][Hide abstract] ABSTRACT: Carcass conformation or morphology in sheep is an important trait for breeders, farmers and meat traders. The commercial value of carcasses is partially based on visual assessment of conformation. This trait is often subject to controversy because of its subjectivity and its weak relationship to muscle yield. The aims of this report are to present results on the biological significance of conformation and to evaluate the reliability of conformation assessment for the genetic improvement of butcher's qualities. This report is a synthesis of three independent studies, each based on the comparison of two genetic types, one with a good conformation and the other with a worse conformation. Conformation reflects muscle morphology, especially muscle deepness which is an important trait when retail products are whole carcasses or joints. Modification of individual muscle thickness is differential according to anatomical location. Conformation improvement increases carcass yield and muscle yield. Muscle to bone ratio is also increased, corresponding to a reduction of bone percentage and sometimes to an increase of muscle percentage. Often, individual muscle weights showed differential repartition on carcass segments. Fatness is not increased. Muscle thickness increase is related to a switch of contractile traits to fast myosin isoforms. These studies have shown that some modifications of biological features are rather related to breed characteristics than to a better conformation.
No preview · Article · Feb 2002 · Productions Animales -Paris- Institut National de la Recherche Agronomique-
[Show abstract][Hide abstract] ABSTRACT: A genome-wide linkage disequilibrium (LD) map was generated using microsatellite genotypes (284 autosomal microsatellite loci) of 581 gametes sampled from the dutch black-and-white dairy cattle population. LD was measured between all marker pairs, both syntenic and nonsyntenic. Analysis of syntenic pairs revealed surprisingly high levels of LD that, although more pronounced for closely linked marker pairs, extended over several tens of centimorgan. In addition, significant gametic associations were also shown to be very common between nonsyntenic loci. Simulations using the known genealogies of the studied sample indicate that random drift alone is likely to account for most of the observed disequilibrium. No clear evidence was obtained for a direct effect of selection ("Bulmer effect"). The observation of long range disequilibrium between syntenic loci using low-density marker maps indicates that LD mapping has the potential to be very effective in livestock populations. The frequent occurrence of gametic associations between nonsyntenic loci, however, encourages the combined use of linkage and linkage disequilibrium methods to avoid false positive results when mapping genes in livestock.
[Show abstract][Hide abstract] ABSTRACT: Growth performance data (weights and daily gains from birth to 130 days of age) of 3,082 lambs born from January 1989 to December 1996 in 158 flocks in the Southern part of Belgium were analysed to estimate non genetic effects and genetic parameters. Using a least-squares procedure and a linear model, non genetic effects of herd, sex, rearing types (artificial rearing, natural rearing with single lamb, with 2 lambs and with 3 lambs ), season and year of birth have been examined, showing the importance of the herd during the whole growth periode, and of the rearing type between 10 and 30 days of age. A single trait animal model and a REML procedure have been used to estimate variance components (genetic additive, management group and residual variances). The heritabilities computed from those variance components estimates ranged from 0.4 to 0.56.
No preview · Article · Mar 1999 · Annales de médecine vétérinaire
[Show abstract][Hide abstract] ABSTRACT: A whole genome scan was undertaken in a granddaughter design comprising 1158 progeny-tested bulls in order to map QTL influencing
milk yield and composition. In this paper we report the identification of a locus on the centromeric end of bovine Chromosome
(Chr) 14, with major effect on fat and protein percentage as well as milk yield. The genuine nature of this QTL was verified
using the grand2-daughter design, that is, by tracing the segregating QTL alleles from heterozygous grandsires to their maternal grandsons
and confirming the predicted QTL allele substitution effect.
[Show abstract][Hide abstract] ABSTRACT: As part of a whole genome scan undertaken to detect quantitative trait loci (QTL) affecting milk yield and composition, we have genotyped a granddaughter design comprising 1152 sons for six microsatellite markers spanning bovine chromosome 20. An analysis performed across families provided strong evidence (experiment-wise P-values < 0.01) for the presence of a QTL affecting primarily protein percentage towards the telomeric end of the chromosome. A founder sire, shown in a previous study to segregate for a similar QTL in the corresponding chromosome region, was characterized by 29 and 57 sons and maternal grandsons, respectively, in the present design. Sorting corresponding sons and grandsons by paternal or grandpaternal allele provided significant evidence for the segregation of a QTL on chromosome 20. Altogether these results confirm the location of a QTL affecting milk production on bovine chromosome 20.