Abstract
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.
Highlights
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
BCAR4 appears involved in embryonic development in vitro, but its role during in vivo embryo development, as well as its expression and function during folliculogenesis, remains uncharacterised
This study shows for the first time that BCAR4 is transcribed in ovarian preantral follicles
Summary
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. Over the past twenty years, the combination of expressional and functional genomics has unveiled a number of mammalian genes whose preferential expression in the oocyte is often associated with a role in ovarian folliculogenesis, fertilisation, or early embryonic development[1,2,3]. Following microinjection of siRNA into in vitro matured bovine oocytes, BCAR4-knocked-down embryos displayed a compromised development to the morula stage. A second argument for rabbit as model organism relates to ovarian development, which is convenient for studying in offspring In this species, meiosis is initiated at birth in the female gonad. Females carrying an altered BCAR4 gene, in parallel with their control wild-type littermates, were analysed on several parameters related to ovarian physiology and reproduction
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