Skip to Main Content

Oct-4 Expression in the Equine Embryo

Abby Obermiller, Young-Ho Choi, Katrin Hinrichs

Veterinary Physiology and Pharmacology, Texas A&M College of Veterinary Medicine, College Station, Texas, USA


The transcription factor Oct-4 is thought to be an essential factor in controlling early embryonic development and pluripotency.  Oct-4 expression in the mouse and rhesus monkey is low in early cleavage-stage embryos, appears at the 16-cell stage and is expressed only in the inner cell mass at the blastocyst stage.  Recent studies in porcine and bovine embryos have shown significant differences in Oct-4 expression compared to that of the mouse and monkey.     No work on Oct-4 expression has been performed in the horse.  This study investigated the expression pattern of Oct-4 in the early equine embryo, as determined by immunocytochemistry in oocytes and developing preimplantation embryos.  Immature oocytes expressed Oct-4 in the cytoplasm and germinal vesicle.  Early embryos also showed cytoplasmic and nuclear staining.  Staining in both compartments decreased from Day 1 to Day 4.  Nuclear, but not cytoplasmic, staining then increased from Day 5 to Day 7.  In blastocysts, Oct-4 staining was present in both the inner cell mass and in the trophoblast.  However, staining appeared to be more vivid in the inner cell mass, and allowed visualization of the inner cell mass not possible under DAPI staining.  Some trophoblast nuclei did not stain for Oct-4.  Better understanding of Oct-4 and its expression will contribute to knowledge of the biology of the equine embryo, as well as aiding researchers in the study of stem cells by potentially providing a reliable marker for pluripotent embryonic stem cells in this species.