Identification d'un gène majeur influençant le taux d'ovulation en race ovine Lacaune

Chez les ovins, la prolificité est un critère important sélectionné pour la production d'agneaux. En race Lacaune, une mutation autosomale (FecL, chromosome 11 ovin) qui augmente le taux d'ovulation et donc la prolificité des brebis a été mise en évidence. Les objectifs de cette thèse étaient d'une part, la localisation fine et le clonage positionnel de FecL et d'autre part, la caractérisation des conséquences physiologiques de la mutation. Une centaine de marqueurs génétiques ont été développés à partir des séquences disponibles, puis par séquençage haut débit. Le génotypage de familles expérimentales a permis de réduire le locus FecL à une région de 190 kb qui comprend deux gènes, IGF2BP1 et B4GALNT2. Différents éléments, tels que la présence d'un SNP dans un intron du gène B4GALNT2 en total déséquilibre de liaison avec la mutation et une très forte surexpression des ARNm de B4GALNT2 dans les ovaires des brebis mutées, désignent ce gène comme le gène FecL. Au niveau physiologique, les brebis mutées sont caractérisées par un plus grand nombre de follicules matures et une expression augmentée du récepteur à FSH dans l'ovaire, une concentration plus élevée en œstradiol circulant qui entraine une accélération de la pulsatilité et une décharge préovulatoire de LH plus précoce. L'hypothèse retenue serait une action de FecL sur le phénomène de sélection des follicules conduisant à une augmentation du taux d'ovulation. Jusqu'à présent, dans l'espèce ovine, toutes les mutations identifiées influençant le taux d'ovulation concernent le système TGFß. Cette thèse met en évidence une nouvelle voie de régulation de la fonction ovarienne et du taux d'ovulation chez la brebis.In sheep, prolificacy is a important criteria selected in lamb production. In the Lacaune breed, an autosomal mutation (FecL, chromosome 11) increasing ovulation rate and therefore ewes prolificacy has been evidenced. The goals of this work were on one hand, the fine mapping of FecL, and on the other hand, the endocrine characterization of the reproductive axis in highly prolific Lacaune sheep. About one hundred markers have been developed first from available sequences then from high-throughput sequencing. Genotyping of experimental families led to a locus of 190kb containing FecL, encompassing two genes, IGF2BP1 and B4GALNT2. The presence of a SNP completely associated with the mutation localized in an intron of B4GALNT2 gene and the over expression of B4GALNT2 mRNA in mutated ovaries led us to consider this gene as the FecL gene. Physiologically, the mutated ewes have a greater number of mature follicles and an over expression of the FSH receptor in ovary, a higher plasmatic oestradiol concentration leading to a higher LH pulsatility and then a precocious LH preovulatory surge. One hypothesis could be that FecL influences follicles selection leading to an increased ovulation rate. Until now, in sheep breed, all the identified mutations influencing ovulation rate belong to the TGFß system. This work evidences a new regulatory pathway of the ovary function and ovulation rate in ewes

Assessing the age-related relationship between plasma anti-Müllerian Hormone (AMH) and ovarian follicle population in prepubertal ewes (abstract)

Publishe

Identification d'un gène majeur influençant le taux d'ovulation en race ovine Lacaune

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Mutations in two genes are associated with increased ovulation rate and litter size in progeny of Lacaune meat sheep

A new autosomal major gene affecting ovulation has been evidenced by a statistical approach in the Lacaune population. A full genome scan localized this autosomal prolificacy gene (FecL) on sheep chromosome 11. Further investigations allowed the reduction of the localization interval between markers BM17132 and FAM117A, corresponding to one synteny block of human chromosome 17 of 1.1 megabases, containing 20 genes. This fine mapping is still going on. The expression of those 20 genes was tested by qPCR and no difference was found in homozygous mutants versus wild type, in four tissues (granulosa and theca cells, hypothalamus and pituitary gland). A particular haplotype was associated with the FecL mutation, which allowed marker associated classification of animals as carriers or non-carriers of the mutation. In addition, ewes with extreme ovulation rate have been isolated in the Lacaune population and it was hypothesized that another mutation was segregating in the population. A new mutation has been evidenced in the Bmp15 coding sequence (chromosome X). This mutation is a non conservative substitution (C53Y) that prevents the processing of the protein. Synergic action of the two mutations (in FecL and Bmp15 genes) on both ovulation rate and litter size was demonstrated

L'efficacité alimentaire en cuniculture : impacts technico-économiques et environnementaux

L'efficacité alimentaire est un indicateur essentiel pour juger de la performance et de la rentabilité d'un système d'élevage. En cuniculture, l'indice de consommation technique (maternité+engraissement) est passé de 3,8 à 3,4 durant les 15 dernières années. Ainsi, les rejets azotés et phosphorés ont été réduits d'environ 10%. Cette amélioration provient des progrès conjoints sur : la maîtrise sanitaire, les techniques d'alimentation (notamment le rationnement), la maîtrise du logement (ventilation, température, etc.) et le potentiel génétique. Cette synthèse résume l'impact de ces différents paramètres sur l'efficacité alimentaire. A l'avenir, il semble possible d'améliorer encore l'efficacité alimentaire, et donc de réduire à la fois les intrants et les rejets, pour atteindre un indice de consommation technique d'environ 3,0, comparable à celui enregistré en système porcin

Efficacité alimentaire en cuniculture : voies d'améliorations, impacts technico-économiques et environnementaux

Despite substantial advances in breeding efficiency over the last 40 years, feed still represents the majority of production cost (+/- 60 %). Feed efficiency, mostly expressed as Feed Conversion Ratio (FCR), is a key indicator to judge the financial and environmental performance of a farming system. Moreover, by improving the feed efficiency, excretion and gas losses in the environment are reduced. In conventional rabbit farming, the farm FCR (maternity + fattening units) in European farms was decreased by 10 % (decrease from 3.8 to 3.4) during the past 15 years, as well as nitrogen and phosphorus excretion. This improvement can be attributed to joined progresses in health control, feeding strategies (including feed restriction), housing management and genetic potential of animals. This review summarizes the impact of various factors to improve FCR for conventional rabbit farming. To optimize rabbit farm FCR, the reproducing stock as well as the fattening unit must be considered. After the sanitary management, the reproductive performances of the flock are a good leverage to improve farm FCR. The use of balanced diets preserving digestive health of the growing rabbit, together with an appropriate feeding restriction after weaning, is also a good leverage. Research in genetics also contributes in lowering farm FCR, by two ways: increasing the growth rate and/or reducing the feed intake for a fixed growth. The environmental impact of rabbit production varies between 7.6 and 10.5 kg of CO2 equivalent/kg of carcass produced (slightly higher than chicken) and does not differ from that of pork. In perspectives, further improvements of feed efficiency, and reductions in feed input and output in environment, should lead to a farm FCR of 3.0, similar to that of pig production

Quantitative genetics of feed efficiency in ducks

Given the worldwide diversity of duck production, genetics aspects of feed efficiency of ducks should be addressed depending on the production (broilers, layers, and “foie gras”) and on the genetic types (Muscovy duck, common duck, and their intergeneric cross mainly used in France for “foie gras” production after force-feeding, i.e. the mule duck). The two main criteria to characterize feed efficiency are the feed conversion ratio (FCR), computed as the ratio of food quantity divided by the output, and the residual feed intake (RFI) which is obtained through a multiple linear regression of feed intake by output and metabolic requirements. The former is a ratio, with undesirable statistic properties. In addition, it is uneasy to disentangle variations in net feed efficiency from variations in FCR due to production traits. The latter is supposed to be, at least phenotypically, independent from the constituent production traits. This is the reason why it gained popularity, even though it requires a thorough analysis of metabolic requirements, as in the overfed mule ducks, where the fat deposition capacity should not be impaired. In the literature, the values found for FCR depend on the genetic type and on the production: FCR≈2.5 at 12 wk. for male Muscovy and FCR >3.2 at 13 wk. for fatty mule ducks; FCR ≈ 1.9 at 42d for Pekin broilers; FCR ≈2.8 for layers. Usually RFI is moderately heritable (h²≈0.25 in layers; 0.3<h²<0.4 in Pekin broilers) and slightly more heritable than FCR. RFI heritability of fattened mule ducks needs to be refined. Genetic correlations between FCR and RFI vary between studies, from moderate (ρG=+0.34) to high (ρG=+0.99). Reliable assessment of individual feed intake is an issue. Development of RFID based automatic feeders greatly helped the improvement of feed efficiency in duck breeding programs. Such devices open the field for new studies, as they give access to feeding behavioral traits. They also allow for the joint modeling of trajectories for feed intake and production traits. Finally, as a complex trait, selection for feed efficiency should benefit from the availability of molecular tools

B4GALNT2, a new major fecundity gene in the Lacaune ovine breed

National audienc

Use of combined in silico expression data and phylogenetic analysis to identify new oocyte genes encoding RNA binding proteins in the mouse

International audienceDuring folliculogenesis, oocytes accumulate maternal mRNAs in preparation for the first steps of early embryogenesis. The processing of oocyte mRNAs is ensured by heterogeneous nuclear ribonucleoproteins (hnRNPs) genes that encode RNA binding proteins implied in mRNA biogenesis, translation, alternative splicing, nuclear exportation, and degradation. In the present work, by combining phylogenetic analyses and, when available, in silico expression data, we have identified three new oocyte-expressed genes encoding RNA binding proteins by using two strategies. Firstly, we have identified mouse orthologs of the Car1 gene, known to be involved in regulation of germ cell apoptosis in C. elegans, and of the Squid gene, required for the establishment of anteroposterior polarity in the Drosophila oocyte. Secondly, we have identified, among genes whose ESTs are highly represented in oocyte libraries, a paralog of Poly(A) binding protein-Interacting Protein 2 (Paip2) gene, known to inhibit the interaction of the Poly(A)-Binding Protein with Poly(A) tails of mRNAs. For all of these genes, the expression in oocyte was verified by in situ hybridization. Overall, this work underlines the efficiency of in silico methodologies to identify new genes involved in biological processes such as oogenesis. Mol. Reprod. Dev. 75: 1691-1700, 2008. (c) 2008 Wiley-Liss, Inc