Quantitative immunogold ultracryomicrotome stidies of the distribution of periimplantation proteins in the sheep

Summary

Several mammalian uterine and conceptus proteins are produced at specific stages of implantation. Ovine trophoblast protein-1 (OTP-1) is only synthesised of pregnancy (dpc). This immunogold ultracryosection study shows that, during this period, OTP-1 immunoreactivity is only found in the Golgi body of the trophectodermal cells. A second protein, of 14 kD molecular weight (14K protein), has a more varied distribution being found in membrane-bounded crystals in uterine epithelium and trophectodermal cells, and distributed throughout the cytosol and nucleoplasm of the uterine epithelium. There are only trace amounts of the 14 K protein in the fetomaternal syncytium which replaces the uterine epithelium during implantation, and no crystals are found in the trophectoderm after cotyledonary villus formation is initiated at 24–25 dpc. The crystals containing 14 K protein persist throughout pregnancy in the intercotyledonary areas. The narrow time window of OTP-1 occurrence reinforces the suggestion that this represents an important developmental signal, whereas the distribution of the 14 K protein indicates a more general nutritive function.