Maternal/zygotic knockout and droplet digital polymerase chain reaction analysis question the role of activin A in preimplantation mouse embryo development†

For many years, activin A, encoded by Inhba, has been thought to be present in both mouse and human oocytes and preimplantation embryos. However, its deficiency does not impede the proper embryonic development of the embryo until birth. It has been suggested that the lack of a phenotype in zygotic knockout embryos may be masked by the presence of maternal protein deposited in the oocyte during oogenesis or provided from the reproductive tract. Therefore, to explore whether maternally supplied activin A is required for embryo development, we carried out a conditional Inhba knockout in oocytes using Zp3-Cre/LoxP strategy. By examining Inhba maternal and maternal/zygotic knockout embryos, individually recorded using time-lapse imaging, immunostained, and genotyped, we revealed that the maternal pool of activin A affects the dynamics of mouse preimplantation development. These alterations are accompanied by impaired mitochondrial activity in oocytes. Surprisingly, using the droplet digital polymerase chain reaction approach, we provided evidence that the Inhba mRNA of zygotic origin is undetectable in mouse embryos.