Mono or poly ovulation, evolutionary role of the BMP15 gene in mammals – MONOPOLY

To carry out our project we use physiology methodological approaches at the cellular and molecular levels (study of gene activity) and animal genetics (study of mutations). We are supported by software tools for analyzing biological data banks.
Physiology approaches involve the isolation of the oocyte, the female reproductive cell in which the BMP15 gene operates. Although this is the largest cell in the body (20µm), the oocyte is a single cell within the ovarian follicles and it must be isolated and captured using a laser cutting. Once isolated, we collect the genetic material (DNA and RNA) located within the oocytes and using amplification and quantification techniques, we measure the level of BMP15 gene activity (i.e. expression) and we compare it between the different studied species.
From a genetic standpoint, we decipher by DNA sequencing the genetic code of the BMP15 gene in sheep, cows or sows that show significant differences in the number of newborns. Thus we can identify anomalies in the code (i.e. mutation) that explain these differences.
Finally, using the databases of BMP15 genetic codes in different mammal species and their analysis by computer programs, we evaluate the speed of evolution through the ages of the BMP15 gene compared to other genes. We evaluated also the genetic selection pressure exerted on this gene.

The first analyses of the BMP15 gene expression in oocytes show that it is 5 times more expressed in sows than in cows, which would run contrary to our concept presented above. But we must determine the level of activity of the gene product, the BMP15 protein, later in the project to really conclude.
At the genetic level, we have identified two anomalies in the genetic code of BMP15 from ewes of the French Grivette (Massif Central) and the Polish Olkuska breeds. In both cases, these ewes carrying those natural mutations may have 4 or 5 lambs at each lambing, but they never become sterile as we have previously seen for other natural mutations appeared elsewhere in the genetic code of BMP15.
Regarding the evolution of the BMP15 gene, we showed that it had evolved faster than other genes of the BMP family (which he is the 15th member). Furthermore, the gene is subject to a positive genetic selection on specific locations of the code, which in theory should give it a selective advantage. We tested this theory by artificially altering the code and we change the gene activity. The artificial modification that we made is also naturally occurring in women with early ovarian insufficiency syndrome, which proves that this region of the BMP15 code is very important for proper ovarian function.

In terms of basic research, this project will increase the knowledge of the role the BMP15 gene in the ovarian function and the control of ovulation rate. From a more applied perspective, the results to be obtained could be used to develop new strategies for reproductive biotechnologies to improve the fertility of farm animals as part of sustainable development of agriculture, or may have clinical implications with the development of new therapies against ovarian pathologies in women. Finally, a direct application of this project is to improve the «genetic marker-assisted selection« in the conduct of French farms sheep, cattle and pigs, with the discovery of new mutations in BMP15 able to predict the number of newborns at each farrowing (i.e. prolificacy).

The first results we obtained were presented to the world scientific community in the fields of animal reproduction and genetics at four international congresses (15th International Congress of Endocrinology, Florence, Italy; 33rd Conference of the International Society of Animal Genetics, Cairns, Australia; 17th International Congress on Animal Reproduction, Vancouver, Canada; 63rd annual Meeting of the European Federation of Animal Science, Bratislava, Slovakia). We have also written three articles for international journals. A review article published in «Mammalian Genome« where we present the current state of global knowledge for the genetic control of ovulation rate in mammals. We proposed an article to the «Human Mutation« journal on the genetic evolution of the BMP15 gene. Finally, we proposed an article to the «PLoS Genetics« journal about the discovery of two new BMP15 mutations increasing the number of ovulations in ewes.

Among mammalian species, it exists a strong variability in ovulation rate from 1-2 (human, bovine, ovine) to more than 10 (rodents, porcine) - The ovulation rate can be genetically regulated as demonstrated in ovine species by the discovery of the Bmp-15 fecundity gene. Thus, we aim to determine if BMP15 has specialized during evolution to be considered as 'THE key gene' controlling ovulation rate in mammals. The concept is that fully functional BMP15 would strictly control mono-ovulation, while altered BMP15 action would allow poly-ovulation to occur. Using mono- (woman, cattle) vs. poly-ovulating (sow) species as model, we propose to study the expression and the structure/function of the BMP15 gene in a comparative biology perspective, with the combination of molecular and cellular physiology approaches (expression, cell culture, recombinant protein, transcriptome and proteome) and animal genetics (genotyping, selection). The research we plan to develop in the present project will lead to a better understanding of the ovarian function in farm animals with possible fallout for animal breeding and ovarian diseases in human.