Changing ratio of human chorionic gonadotropin subunits synthesized by early and full-term placental polyribosomes

The diagnostic significance of hCG and hPL via immunohistochemistry of placental tissues in pregnancies diagnosed with IUGR and IUD

Placentas of patients diagnosed with intrauterine growth restriction (IUGR) and intrauterine death (IUD) were examined by immunohistochemistry for alpha-beta subunits of human chorionic gonadotropin (hCG) and human placental lactogen (hPL) antibodies, and compared with placentas from women with healthy pregnancies. In total, 114 subjects were evaluated. The patient group comprised 27 cases of IUGR and 57 of IUD, and the control group consisted of 30 women with normal pregnancies. Placental specimens were examined for primary antibodies using immunohistochemical techniques. Placentas from 22 cases of IUGR were stained positively for alpha-hCG. All 27 specimens obtained from this group were stained positively for beta-hCG and hPL. Among the cases of IUD, 44 placentas were stained positively for alpha-hCG, and all 57 specimens were stained positively for beta-hCG and hPL.

Localization of human chorionic gonadoptropin and placental lactogen by immunogold labeling for electron microscopy: technique and limitations

To demonstrate human chorionic gonadotropin (hCG) and human placental lactogen (hPL) secretory granules in placenta and to illustrate newer embedding techniques and specific immunospecificity problems in the placenta, labeling experiments using immunogold or peroxidase combined with avidin-biotin enhancement in epoxy LX-112-, Araldite-, or LR gold-embedded tissue fixed in 2.5% glutaraldehyde or 2.5% paraformaldehyde were carried out in term and first-trimester normal human placenta and in partial hydatidiform moles. Increased sensitivity of the low-temperature LR gold method was found for hPL-labeled granules. beta hCG-labeled granules were noted in syncytium of first-trimester placenta, and beta hCG-containing granules in hydatidiform moles were similar to those of normal placenta. Paraformaldehyde fixation and LR gold embedding permitted identification of endoplasmic reticulum-associated labeling not observed with other methods. A brief review and discussion of immunolabeling methods, controls, and embedding materials is presented. We conclude that further refinement of peptide localization methods in the placenta is possible but must take into account the abundant potentially cross-reacting peptides present in the placenta.

Isolation of ribosomal subunits containing intact rRNA from human placenta: estimation of functional activity of 80S ribosomes

We have elaborated a method for the isolation of ribosomal subunits from fresh unfrozen human placenta containing intact rRNA and a complete set of ribosomal proteins. Activity of 80S ribosomes obtained by reassociation of 40S and 60S subunits in nonenzymatic poly(U)-dependent binding of Phe-tRNA(Phe) was equal to 80% (above 1.5 mol [14C]Phe-tRNA(Phe) is coupled to 1 mol of ribosomes). The activity of 80S ribosomes in poly(U)-directed synthesis of polyphenylalanine was tested in a polysome-free protein-synthesizing system from rabbit reticulocytes. About 100 mol of phenylalanine residue was polymerized by a mole of ribosomes at a rate of 0.83 residues per minute in this system (2 h, 37 degrees C).

Immunolocalization of alpha and beta chains of human chorionic gonadotropin, placental lactogen and pregnancy-specific beta-glycoprotein in term placenta by a touch preparation method

Touch preparations of human placenta yield cells retaining antigenic reactivity to immunoperoxidase stains for alpha and beta chains of human chorionic gonadotropin, placental lactogen, and pregnancy-specific beta glycoprotein. This method is a rapid and simple alternative to conventional frozen and paraffin-embedded sections for detection of placental peptides.

Only three of the seven human chorionic gonadotropin beta subunit genes can be expressed in the placenta

Human chorionic gonadotropin (hCG) is a placental hormone essential for the maintenance of pregnancy. While the alpha subunit of this hormone is encoded by a single gene, the beta subunit is encoded by a complex family of seven very similar genes or pseudogenes. Two approaches have been taken to establish which of these genes are functional. First, we have used two restriction enzyme site polymorphisms to correlate 15 independently isolated beta hCG cDNA clones with their corresponding genes. Second, we have used transient expression in COS cells to assay for correctly-initiated transcription from six of the seven beta hCG gene promoters. From these data, we conclude that, at most, only three of the seven beta hCG genes are expressed in the placenta. Comparison of the sequences of a functional and a non-functional beta hCG gene reveals no obvious differences, such as promoter changes, that could account for this differential expression.

The effect of protein and RNA synthesis inhibitors on the synthesis and secretion of hCG, alpha- and beta-hCG subunits, in organ culture

The relationship between the rate of RNA and protein synthesis and that of and its alpha- and beta-subunits was studied in an organ culture system using RNA and protein synthesis inhibitors. It was found that inhibiting protein synthesis by puromycin or cycloheximide results also in a nearly complete inhibition of the synthesis and/or processing of RNA molecules. Protein synthesis was found to be dependent upon continuous poly A(-) RNA synthesis. The intracellular content of hCG, alpha-hCG and beta-hCG remains constant during the entire incubation period and does not change in response to any of the inhibitors used. However, in the presence of some inhibitors, changes are observed in the amount of the secreted hormone and its two subunits as well as in the association ability of the subunits to form the complete native hormone. Nevertheless, synthesis and secretion of hCG, alpha-hCG and beta-hCG were almost identically affected by alpha-amanitin. These results might suggest that the mRNAs coding for the two subunits have the same relative metabolic stability and/or that these mRNAs are mobilized molecules from free cytoplasmic mRNP pools. The specific alpha- and beta-mRNAs seem to be less stable, however, than the mRNAs coding for the other newly synthesized proteins, since the inhibition of alpha- and beta-hCG synthesis by alpha-amanitin was consistently higher than the corresponding average inhibition of total protein synthesis.

Isolation of ribonuclease-free polysomes from human placenta

Human placenta is known to have a high level of polysome-bound ribonuclease which has hindered the isolation of intact polyribosomes from this tissue. We describe conditions for preparing polysomes devoid of apparent ribonuclease activity from both first trimester and term placenta. This stable preparation was achieved by utilizing buffer at low pH containing 300 mM LiCl and precipitating the polysomes chemically with 200 mM MgCl2. The yield of polysomes obtained by this procedure is 2-2.5 fold greater than that obtained by the conventional method of preparing placental polysomes. The polysomes are considered pure as judged by the ratios of absorbance 260/280 and 260/235. Moreover, the yield of polysomes obtained is greater than 95% of the tissue content and the profile of the polysomes is probably representative of the in vivo population. This is concluded from experiments in which a known amount of labelled chick polysomes was added to fresh placental tissue and the recovery of label and its distribution was analyzed.

The cDNA for the beta-subunit of human chorionic gonadotropin suggests evolution of a gene by readthrough into the 3'-untranslated region

A 579-base pair approximately full-length cDNA which codes for the 145-amino acid long beta-subunit of human chorionic gonadotropin (HCG) has been cloned in the plasmid vector pBR322 and its complete nucleotide sequence determined. A hydrophobic presequence of 20 amino acids can be identified from the nucleotide sequence. The amino acid sequence of the beta-subunit is known to be related to those of the beta-subunits of the other glycoprotein hormones LH, FSH and TSH, but the beta-subunit of HCG is unique in that it contains a C-terminal extension of about 30 amino acids which has no homologous counterpart in the other three hormones. Analysis of the beta HCG cDNA nucleotide sequence suggests that this extension may have arisen by the loss of the termination codon of an ancestral beta-like gene so that most of what was previously the 3'-untranslated region now codes for protein. The beta-subunit of HCG terminates with the codon UAA located 16 bases before the poly(A) in the sequence AAUAAA. This sequence is believed to be a recognition signal involved in either polyadenylation or processing and therefore has a dual role in this gene, serving both a coding and a regulatory function.

Predominance of gonadotropin alpha-subunit resulting from preferential loss of hCG beta production in an established cell line

The BeWo line of trophoblastic cells, maintained in continuous culture since 1966, was employed to investigate the phenomenon of gonadotropin alpha-subunit predominance that exists in several cell lines. The secretion of complete human chorionic gonadotropin (hCG) relative to alpha-subunit was compared in several different BeWo sublines, all of where were derived from BeWo stock roller tube colonies. In all of the BeWo sublines, secretion of hCG originally exceeded secretion of alpha-subunit. With time in culture, however, there was a marked decline in production of hCG/hCG beta, but not in alpha-subunit. Thus it appears that the production of hCG beta by BeWo choriocarcinoma cells is more labile than the production of the alpha-subunit.

Isolation, cloning and sequence analysis of the cDNA for the alpha-subunit of human chorionic gonadotropin

A 621-base pair fragment of the cDNA for the alpha-subunit of human chorionic gonadotropin has been isolated by cloning in a plasmid vector, and the complete nucleotide sequence determined. The entire coding region, including the 24-amino acid pre-sequence and most of the untranslated regions, are present in the fragment.