Investigating the role of BCAR4 in ovarian physiology and female fertility by genome editing in rabbit

Efficient and repeatable in vitro fertilization in rabbits

Rabbits constitute an interesting model to understand gamete interaction and test novel Artificial Reproductive Techniques, but in vitro fertilization (IVF) is particularly problematic in this species. We have conducted a series of experiments to develop a consistent IVF technique. Initially, we checked viability, acrosome integrity, capacitation and motility in ejaculated sperm purified by a density gradient and incubated at different times in three different media: Tyrode's Albumin Lactate Pyruvate (TALP), human tubal fluid (HTF), and Brackett and Oliphant (BO). Total and progressive motility at 10-24 h and linearity from 3 h onwards was significantly higher in BO medium compared to TALP and HTF. Subsequently, cumulus-oocyte complexes (COCs) collected 10 h after induction of ovulation were incubated with sperm in TALP, HTF or BO for 18 h with or without performing sperm pre-incubation for 6 h. Pronuclear formation rate at 18 h was significantly higher in BO compared to other media (∼84 % vs. 17-22 %) and was not improved by pre-incubation. As COCs recovery rate was low at 10 h after induction of ovulation, COCs were collected at 12 h and co-incubated with sperm in BO. Pronuclear formation rate was similar than those obtained in COCs collected at 10 h (∼85 %), and when embryos were allowed to develop in vitro, the protocol yielded high cleavage and blastocyst rates (91 and 59 %, respectively). In conclusion, ejaculated rabbit sperm purified in a density gradient fertilize efficiently COCs collected at 12 h in BO medium.

Characterization of the long noncoding RNA transcriptome in human preimplantation embryo development

PURPOSE

Infertility remains a human health burden globally. Only a fraction of embryos produced via assisted reproductive technologies (ARTs) develop to the blastocyst stage in vitro. lncRNA abundance changes significantly during human early embryonic development, indicating vital regulatory roles of lncRNAs in this process. The aim of this study is to obtain insights into the transcriptional basis of developmental events.

METHODS

scRNA-seq data and SUPeR-seq data were used to investigate the lncRNA profiles of human preimplantation embryos. The top 50 highly expressed unique and shared lncRNAs in each stage of preimplantation development were identified. Comparative analysis of the two datasets was used to verify the consistent expression patterns of the lncRNAs. Differentially expressed lncRNAs were identified and subjected to functional enrichment analysis.

RESULTS

The lncRNA profiles of human preimplantation embryos in the E-MTAB-3929 dataset were similar to those in the GSE71318 dataset. The ratios of overlap among the top 50 highly expressed lncRNAs between two pairs of stages (2-cell stage vs. 4-cell stage and 8-cell stage vs. morula) were aberrantly low compared with those between other stages. Each stage of preimplantation development exhibited unique and shared lncRNAs among the top 50 highly expressed lncRNAs. Among the between-group comparisons, the 2-cell stage vs. 4-cell stage showed the highest number of differentially expressed lncRNAs. Functional enrichment analysis revealed that differentially expressed lncRNAs and their associated super enhancers and RNA binding proteins (RBPs) are closely involved in regulating embryonic development. These lncRNAs could function as important cell markers for distinguishing fetal germ cells.

CONCLUSIONS

Our study paves the way for understanding the regulation of developmental events, which might be beneficial for improved reproductive outcomes.

DMRT1 is a testis-determining gene in rabbits and is also essential for female fertility

DMRT1 is the testis-determining factor in several species of vertebrates, but its involvement in mammalian testes differentiation, where SRY is the testis-determining gene, remains ambiguous. So far, DMRT1 loss-of-function has been described in two mammalian species and induces different phenotypes: Disorders of Sex Development (46, XY DSD) in men and male infertility in mice. We thus abolished DMRT1 expression by CRISPR/Cas9 in a third species of mammal, the rabbit. First, we observed that gonads from XY DMRT1-/- rabbit fetuses differentiated like ovaries, highlighting that DMRT1 is involved in testis determination. In addition to SRY, DMRT1 is required in the supporting cells to increase the expression of the SOX9 gene, which heads the testicular genetic cascade. Second, we highlighted another function of DMRT1 in the germline since XX and XY DMRT1-/- ovaries did not undergo meiosis and folliculogenesis. XX DMRT1-/- adult females were sterile, showing that DMRT1 is also crucial for female fertility. To conclude, these phenotypes indicate an evolutionary continuum between non-mammalian vertebrates such as birds and non-rodent mammals. Furthermore, our data support the potential involvement of DMRT1 mutations in different human pathologies, such as 46, XY DSD as well as male and female infertility.

Fetal Estrogens are not Involved in Sex Determination But Critical for Early Ovarian Differentiation in Rabbits

AROMATASE is encoded by the CYP19A1 gene and is the cytochrome enzyme responsible for estrogen synthesis in vertebrates. In most mammals, a peak of CYP19A1 gene expression occurs in the fetal XX gonad when sexual differentiation is initiated. To elucidate the role of this peak, we produced 3 lines of TALEN genetically edited CYP19A1 knockout (KO) rabbits that were devoid of any estradiol production. All the KO XX rabbits developed as females with aberrantly small ovaries in adulthood, an almost empty reserve of primordial follicles, and very few large antrum follicles. Ovulation never occurred. Our histological, immunohistological, and transcriptomic analyses showed that the estradiol surge in the XX fetal rabbit gonad is not essential to its determination as an ovary, or for meiosis. However, it is mandatory for the high proliferation and differentiation of both somatic and germ cells, and consequently for establishment of the ovarian reserve.

A Comparative Analysis of Oocyte Development in Mammals

Sexual reproduction requires the fertilization of a female gamete after it has undergone optimal development. Various aspects of oocyte development and many molecular actors in this process are shared among mammals, but phylogeny and experimental data reveal species specificities. In this chapter, we will present these common and distinctive features with a focus on three points: the shaping of the oocyte transcriptome from evolutionarily conserved and rapidly evolving genes, the control of folliculogenesis and ovulation rate by oocyte-secreted Growth and Differentiation Factor 9 and Bone Morphogenetic Protein 15, and the importance of lipid metabolism.