The syncytiotrophoblast is a multinuclear cell layer maintained through fusion events with cytotrophoblasts and plays a key role in the properties of the placenta. Monitoring fusion in this cell layer is important in studies aimed at understanding its function. We herein propose a new fusion assay based on the transactivating potential of the human immunodeficiency virus type 1 (HIV-1) Tat protein on its promoter present in the long terminal repeat (LTR) region. We used 2 BeWo cell populations, one stably transfected with the HIV-1 LTR positioned upstream of the luciferase gene and the other stably transfected with a Tat expression vector. Both stable cell lines were responsive to Tat-mediated LTR transactivation and demonstrated normal fusion and human chorionic gonadotropin (hCG) secretion upon stimulation. When both BeWo cell lines were cocultured, forskolin-mediated induction of fusion led to an increase in luciferase activity, which was sensitive to anti-syncytin 1 and -2 antibodies and syncytin 2 small interfering RNAs (siRNAs). Similar results were obtained in primary trophoblasts. Our results highlight the effectiveness and accuracy of this new quantification assay for trophoblast fusion.
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Benirschke K, Kaufmann P. Pathology of the human placenta. In: Verlag S, (ed.), Pathology of the Human Placenta. 4th ed. New York, NY; 2000.
Mi S, Lee X, Li X, et al. Syncytin is a captive retroviral envelope protein involved in human placental morphogenesis. Nature. 2000;403(6771):785–789.
Frendo JL, Olivier D, Cheynet V, et al. Direct involvement of HERV-W Env glycoprotein in human trophoblast cell fusion and differentiation. Mol Cell Biol. 2003;23(10):3566–3574.
Blond JL, Lavillette D, Cheynet V, et al. An envelope glycoprotein of the human endogenous retrovirus HERV-W is expressed in the human placenta and fuses cells expressing the type D mammalian retrovirus receptor. J Virol. 2000;74(7):3321–3329.
Vargas A, Moreau J, Landry S, et al. Syncytin-2 plays an important role in the fusion of human trophoblast cells. J Mol Biol. 2009;392(2):301–318.
Huppertz B, Bartz C, Kokozidou M. Trophoblast fusion: fusogenic proteins, syncytins and ADAMs, and other prerequisites for syncytial fusion. Micron. 2006;37(6):509–517.
Aplin JD, Straszewski-Chavez SL, Kalionis B, et al. Trophoblast differentiation: progenitor cells, fusion and migration—a workshop report. Placenta. 2006;27(suppl A):S141–S143.
Taylor RN, Newman ED, Chen SA. Forskolin and methotrexate induce an intermediate trophoblast phenotype in cultured human choriocarcinoma cells. Am J Obstet Gynecol. 1991;164(1 pt 1):204–210.
Wice B, Menton D, Geuze H, Schwartz AL. Modulators of cyclic AMP metabolism induce syncytiotrophoblast formation in vitro. Exp Cell Res. 1990;186(2):306–316.
Lyden TW, Ng AK, Rote NS. Modulation of phosphatidylserine epitope expression by BeWo cells during forskolin treatment. Placenta. 1993;14(2):177–186.
Borges M, Bose P, Frank HG, Kaufmann P, Potgens AJ. A two-colour fluorescence assay for the measurement of syncytial fusion between trophoblast-derived cell lines. Placenta. 2003;24(10):959–964.
Mounier C, Barbeau B, Vaillancourt C, Lafond J. Endocrinology and cell signaling in human villous trophoblast. Methods Mol Biol. 2009;550:89–102.
Kudo Y, Boyd CA, Kimura H, Cook PR, Redman CW, Sargent IL. Quantifying the syncytialisation of human placental trophoblast BeWo cells grown in vitro. Biochim Biophys Acta. 2003;1640(1):25–31.
Fischer I, Redel S, Hofmann S, et al. Stimulation of syncytium formation in vitro in human trophoblast cells by galectin-1. Placenta. 2010;31(9):825–832.
Barbeau B, Fortin JF, Genois N, Tremblay MJ. Modulation of human immunodeficiency virus type 1-induced syncytium formation by the conformational state of LFA-1 determined by a new luciferase-based syncytium quantitative assay. J Virol. 1998;72(9):7125–7136.
Pare ME, Gauthier S, Sun JF, et al. A new sensitive and quantitative HTLV-I-mediated cell fusion assay in T cells. Virology. 2005;338(2):309–322.
Sun J, Barbeau B, Tremblay MJ. HIV-1-mediated syncytium formation promotes cell-to-cell transfer of Tax protein and HTLV-I gene expression. Virus Res. 2006;118(1–2):120–129.
Garcia JA, Harrich D, Soultanakis E, Wu F, Mitsuyasu R, Baynor RB. Human immunodeficiency virus type 1 LTR TATA and TAR region sequences required for transcriptional regulation. Embo J. 1989;8(3):765–778.
Cullen BR. Trans-activation of human immunodeficiency virus occurs via abimodal mechanism. Cell. 1986;46(7):973–982.
Kliman HJ, Nestler JE, Sermasi E, Sanger JM, Strauss JF 3rd. Purification, characterization, and in vitro differentiation of cytotrophoblasts from human term placentae. Endocrinology. 1986;118(4):1567–1582.
Vargas A, Moreau J, Le Bellego F, Lafond J, Barbeau B. Induction of trophoblast cell fusion by a protein tyrosine phosphatase inhibitor. Placenta. 2008;29(2):170–174.
Benveniste R, Scommegna A. Human chorionic gonadotrophin (HCG) and free alpha subunit secreted by cultured human choriocarcinoma (JEG-3) cells. Placenta Suppl. 1981;3:241–250.
Bergemann C, Reimer T, Muller H, et al. Stimulation of hCG protein and mRNA levels in trophoblast tumour cells Jeg3 and BeWo by glycodelin A. Anticancer Res. 2003;23(2A):1107–1113.
Zachar V, Ebbesen P, Thomas RA, Zacharova V, Goustin AS. Basal and Tat-transactivated expression from the human immunodeficiency virus type 1 long terminal repeat in human placental trophoblast rules out promoter-enhancer activation as the partial block to viral replication. J Gen Virol. 1994;75(pt 6):1461–1468.
Dalton P, Christian HC, Redman CW, Sargent IL, Boyd CA. Membrane trafficking of CD98 and its ligand galectin 3 in BeWo cells—implication for placental cell fusion. FEBS J. 2007;274(11):2715–2727.
Langbein M, Strick R, Strissel PL, et al. Impaired cytotrophoblast cell-cell fusion is associated with reduced Syncytin and increased apoptosis in patients with placental dysfunction. Mol Reprod Dev. 2008;75(1):175–183.
Malassine A, Frendo JL, Evain-Brion D. A comparison of placental development and endocrine functions between the human and mouse model. Hum Reprod Update. 2003;9(6):531–539.
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Vargas, A., Larocque, É., Toufaily, C. et al. A New Luciferase-Based Quantitative Assay for the Evaluation of Human Trophoblast Fusion. Reprod. Sci. 19, 374–382 (2012). https://doi.org/10.1177/1933719111424437
- cell fusion
- human trophoblasts
- syncytin 1
- syncytin 2
- HIV-1 Tat