Bone morphogenetic protein 15 (BMP15), a member of the transforming growth factor beta superfamily, plays an essential role in ovarian follicular development in mono-ovulatory mammalian species. Studies using a biallelic knockout mouse model revealed that BMP15 potentially has just a minimal impact on female fertility and ovarian follicular development in polyovulatory species. In contrast, our previous study demonstrated that in vivo knockdown of BMP15 significantly affected porcine female fertility, as evidenced by the dysplastic ovaries containing significantly decreased numbers of follicles and an increased number of abnormal follicles. This finding implied that BMP15 plays an important role in the regulation of female fertility and ovarian follicular development in polyovulatory species. To further investigate the regulatory role of BMP15 in porcine ovarian and follicular development, here, we describe the efficient generation of BMP15edited Yorkshire pigs using CRISPR/Cas9. Using artificial insemination experiments, we found that the biallelically edited gilts were all infertile, regardless of different genotypes. One monoallelically edited gilt #4 (Δ66 bp/WT) was fertile and could deliver offspring with a litter size comparable to that of wild-type gilts. Further analysis established that the infertility of biallelically edited gilts was caused by the arrest of follicular development at preantral stages, with formation of numerous structurally abnormal follicles, resulting in streaky ovaries and the absence of obvious estrous cycles. Our results strongly suggest that the role of BMP15 in nonrodent polyovulatory species may be as important as that in mono-ovulatory species.

Summary sentence

Examination of BMP15-edited cloned pigs indicated that loss of function of BMP15 severely affects porcine female fertility, mainly because of the inhibition of follicular development into the antral stage.