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

Breast Cancer Anti-estrogen Resistance 4 (BCAR4) was previously characterised in bovine species as a gene preferentially expressed in oocytes, whose inhibition is detrimental to in vitro embryo development. But its role in oogenesis, folliculogenesis and globally fertility in vivo remains unknown. Because the gene is not conserved in mice, rabbits were chosen for investigation of BCAR4 expression and function in vivo. BCAR4 displayed preferential expression in the ovary compared to somatic organs, and within the ovarian follicle in the oocyte compared to somatic cells. The transcript was detected in follicles as early as the preantral stage. Abundance decreased throughout embryo development until the blastocyst stage. A lineage of genome-edited rabbits was produced; BCAR4 expression was abolished in follicles from homozygous animals. Females of wild-type, heterozygous and homozygous genotypes were examined for ovarian physiology and reproductive parameters. Follicle growth and the number of ovulations in response to hormonal stimulation were not significantly different between genotypes. Following insemination, homozygous females displayed a significantly lower delivery rate than their heterozygous counterparts (22 ± 7% vs 71 ± 11% (mean ± SEM)), while prolificacy was 1.8 ± 0.7 vs 6.0 ± 1.4 kittens per insemination. In conclusion, BCAR4 is not essential for follicular growth and ovulation but it contributes to optimal fertility in rabbits.