Embryonic POU5F1 is Required for Expanded Bovine Blastocyst Formation

<jats:title>Abstract</jats:title><jats:p>POU5F1 is a transcription factor and master regulator of cell pluripotency with indispensable roles in early embryo development and cell lineage specification. The role of embryonic POU5F1 in blastocyst formation and cell lineage specification differs between mammalian species but remains completely unknown in cattle. The CRISPR/Cas9 system was utilized for targeted disruption of the <jats:italic>POU5F1</jats:italic> gene by direct injection into zygotes. Disruption of the bovine <jats:italic>POU5F1</jats:italic> locus prevented blastocyst formation and was associated with embryonic arrest at the morula stage. POU5F1 knockout morulas developed at a similar rate as control embryos and presented a similar number of blastomeres by day 5 of development. Initiation of SOX2 expression by day 5 of development was not affected by lack of POU5F1. On the other hand, CDX2 expression was aberrant in embryos lacking POU5F1. Notably, the phenotype observed in bovine <jats:italic>POU5F1</jats:italic> knockout embryos reveals conserved functions associated with loss of human embryonic POU5F1 that differ from <jats:italic>Pou5f1</jats:italic>- null mice. The similarity observed in transcriptional regulation of early embryo development between cattle and humans combined with highly efficient gene editing techniques make the bovine a valuable model for human embryo biology with expanded applications in agriculture and assisted reproductive technologies.</jats:p>