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

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

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

Genetic control of multiple births in low ovulating mammalian species

In mammals, litter size is a highly variable trait. Some species such as humans or cattle are monotocous, with one or sometimes two newborns per birth, whereas others, the polytocous species such as mice or pigs, are highly prolific and often produce a dozen newborns at each farrowing. In monotocous species, however, two or three newborns per birth may sometime be unwanted. In more polytocous species such as sheep or pigs, litter size is studied in order to increase livestock prolificacy. By contrast, twinning rates in humans or cattle may increase birth difficulties and health problems in the newborns. In this context, the aim of our review was to provide a clearer understanding of the genetic and physiological factors that control multiple births in low-ovulating mammalian species, with particular focus on three species: sheep, cattle, and humans, where knowledge of the ovulation rate in one may enlighten findings in the others. This article therefore reviews the phenotypic and genetic variability observed with respect to ovulation and twinning rates. It then presents the QTL and major genes that have been identified in each species. Finally, we draw a picture of the diversity of the physiological mechanisms underlying multiple ovulation. Although several major genes have been discovered in sheep, QTL detection methods in humans or cattle have suggested that the determinism of litter size is complex and probably involves several genes in order to explain variations in the number of ovulations

Presence of causative mutations affecting prolificacy in the Noire du Velay and Mouton Vendéen sheep breeds

For many decades, prolificacy has been selected in meat sheep breeds as a polygenic trait but with limited genetic gain. However, the discovery of major genes affecting prolificacy has changed the way of selection for some ovine breeds implementing gene-assisted selection as in the French Lacaune and Grivette meat breeds, or in the Spanish Rasa Aragonesa breed. Based on statistical analysis of litter size parameters from 34 French meat sheep populations, we suspected the segregation of a mutation in a major gene affecting prolificacy in the Noire du Velay and in the Mouton Vendeen breeds exhibiting a very high variability of the litter size. After the genotyping of mutations known to be present in French sheep breeds, we discovered the segregation of the FecL(L) mutation at the B4GALNT2 locus and the FecX(Gr) mutation at the BMP15 locus in Noire du Velay and Mouton Vendeen, respectively. The frequency of ewes carrying FecL(L) in the Noire du Velay population was estimated at 21.2% and the Mouton Vendeen ewes carrying FecX(Gr) at 10.3%. The estimated mutated allele effect of FecL(L) and FecX(Gr) on litter size at + 0.4 and + 0.3 lamb per lambing in Noire du Velay and Mouton Vendeen, respectively. Due to the fairly high frequency and the rather strong effect of the FecL(L) and FecX(Gr) prolific alleles, specific management programmes including genotyping should be implemented for a breeding objective of prolificacy adapted to each of these breeds