Cytological events involved in protein synthesis in cellular and syncytial trophoblast of human placenta. An electron microscope autoradiographic study of [3H]leucine incorporation.

Abstract

Electron microscope autoradiography has been used to study protein synthesis in syncytial and cellular trophoblast of term human placental villi incubated in vitro with tritiated leucine ([aH]leu). Autoradiographs were analyzed using the hypothetical grain analysis of Blackett and Parry (1973. J. Cell Biol. 57:9-15). The results of this study demonstrated that both cellular and syncytial trophoblast have marked capacities for protein synthesis. Cellular trophoblast synthesized protein in both its rough endoplasmic reticulum (RER) and its ground plasm which contained abundant free ribosomes. The vast majority of all-proteins remained within the cell, with some of the proteins synthesized ultimately appearing in the nucleus. A small percentage of grains was ultimately associated with the trophoblast basement membrane. In syncytial trophoblast, the RER was the dominant site for protein synthesis. The autoradiographic data suggested that, as in the cellular trophoblast, the vast majority of all-proteins synthesized by the syncytial trophoblast remained within the syncytial trophoblast throughout the incubation period. The major portion of [aH]leu-labeling present in the syncytial trophoblast of villi incubated the longest times (4 h+) remained in association with the RER. Labeled proteins did not become concentrated in syncytial trophoblast Golgi apparatus, vesicles, or granules. In contrast to cellular trophoblast, the nuclei in the syncytium did not contain 3H-proteins at any timepoint studied.KEY WORDS placenta electron microscopy protein synthesis autoradiography 9 trophoblast Human placental syncytial trophoblast is unique in being the only syncytial epithelium in the body and in releasing its secretory products directly into a blood vascular space. The placenta synthesizes a number of proteins which are secreted into the maternal circulation in high quantities but are found in the fetal circulation in only small amounts (see reference 19 for review). The best characterized of these proteins are human chorionic gonad-400

Cytological events involved in glycoprotein synthesis in cellular and syncytial trophoblast of human placenta. An electron microscope autoradiographic study of [3H]galactose incorporation.

“…This result is in striking contrast to that found in the preceding study of [aH]leucine incorporation by trophoblast where both cellular and syncytial trophoblast exhibited marked capacities for incorporation of the radioactive amino acid (35). Within cytotrophoblast, the RER incorporated the most [3H]gal into glycoprotein.…”

“…Tissue preparation and incubation conditions were as described in the preceding paper (35), except that Medium 199 (M199) contianed [~H]leueine ([IH]leu) and the radioactive label was 250 t~Ci/ml (= 42 /~M) ~ [1-3H]galactose ([gH]gal) (New England Nuclear (Boston, Mass. ); lot no.…”

“…In the preceding paper, both cellular and syncytial trophoblast were demonstrated to have marked capacities for the incorporation of [3H]leucine into proteins (35). To investigate the capacity of both forms of trophoblast to incorporate monosaccharide into macromolecules, term human placental villi were incubated with [SH]galactose and incorporation of radioactivity was followed by electron microscope autoradiography.…”

Nonuniform Distribution and Grouping of Insulin Receptors on the Surface of Human Placental Syncytial Trophoblast

“…sections of tissue as previously described. 28 Preparation offerritin-insulin. Ferritin-insulin conjugates (F-I) and monomeric ferritin-insulin (Fm-I) used in this study were prepared as previously described.…”

Morphology and glycoprotein synthesis of uterine glandular epithelium in human basal plate at term: An ultrastructural and autoradiographic study

“…These sections were heat-annealed to clean glass slides and coated with Kodak NTB-2 emulsion as previously described (Nelson et al, 1978). Emulsion was previously tested for background and sensitivity prior to its use for coating slides.…”