A Novel Functional Role for the Oocyte-Specific Transcription Factor Newborn Ovary Homeobox (NOBOX) during Early Embryonic Development in Cattle

Newborn ovary homeobox (NOBOX) is an oocyte-specific transcription factor essential for folliculogenesis and expression of many germ cell-specific genes in mice. Here we report the characterization of the bovine NOBOX gene and its role in early embryogenesis. The cloned cDNA for bovine NOBOX contains an open reading frame encoding a protein of 500 amino acids with a conserved homeodomain. mRNA for NOBOX is preferentially expressed in ovaries and undetectable by RT-PCR in somatic tissues examined. NOBOX protein is present in oocytes throughout folliculogenesis. NOBOX is expressed in a stage-specific manner during oocyte maturation and early embryonic development and of maternal origin. Knockdown of NOBOX in early embryos using small interfering RNA demonstrated that NOBOX is required for embryonic development to the blastocyst stage. Depletion of NOBOX in early embryos caused significant down-regulation of genes associated with transcriptional regulation, signal transduction, and cell cycle regulation during embryonic genome activation. In addition, NOBOX depletion in early embryos reduced expression of pluripotency genes (POU5F1/OCT4 and NANOG) and number of inner cell mass cells in embryos that reached the blastocyst stage. This study demonstrates that NOBOX is an essential maternal-derived transcription factor during bovine early embryogenesis, which functions in regulation of embryonic genome activation, pluripotency gene expression, and blastocyst cell allocation.