M.S. Ortega1, J.B. Cole2, T.E. Spencer1, and P.J. Hansen3
1Department of Animal Sciences, University of Missouri, Columbia 65211
2AGIL, ARS, USDA
3Department of Animal Sciences, University of Florida, Gainesville
2018 J. Dairy Sci. (?)
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Early pregnancy events in cattle include the ovulation of a competent oocyte, adequate sperm transport in the reproductive tract, and successful fertilization. The newly formed single-cell totipotent zygote relies mostly on maternally-derived mRNA stored in the oocyte for new protein synthesis until the activation of the embryonic genome at the eight-cell stage. By day 7, the embryo has developed into a multicellular blastocyst composed of a pluripotent inner cell mass and a differentiated trophectoderm. After hatching from the zona pellucida, the blastocyst undergoes elongation starting on day 13-14. The elongating conceptus secretes interferon tau (IFNT), which constitutes the signal for maternal recognition of pregnancy and induces the expression of IFN-stimulated genes that regulate uterine receptivity and conceptus elongation. After day 19 in cattle, adhesion of the conceptus to the luminal epithelium starts the process of placentation that involves differentiation of trophoblast giant binucleate cells, which are crucial for the formation of placentomes, nutrition of the fetus, and placental growth to term. All of the above-mentioned events are controlled by many gene systems and, to date, most of the identified mutations are loss-of-function alleles that are often lethal to embryos, such as the spliceosome associated protein homolog (CWC15). However, mutations associated with fertility indices, such as daughter pregnancy rate, have been identified in genes involved in a variety of processes, including oocyte quality (COQ9); fertilization (BSP3); formation of the trophectoderm in the embryo (WBP1); and lipid biosynthesis, which plays a central role in conceptus growth and cell signaling (ACAT2, HSD17B7 and HSD17B12). Functional studies, such as knock-outs in these genes, represent opportunities to better understand the tight regulation of reproductive processes in cattle.