Cell Fusion pp 363-382 | Cite as

Fusion Assays and Models for the Trophoblast

  • Sascha Drewlo
  • Dora Baczyk
  • Caroline Dunk
  • John Kingdom
Part of the Methods in Molecular Biology™ book series (MIMB, volume 475)


A healthy syncytium in the placenta is vital to a successful pregnancy. The trophoblast builds up the natural barrier between the mother and the developing fetus and is the site of gas, nutrition, and waste exchange. An inadequate formation of this tissue leads to several pathologies of pregnancy, which may result in fetal death during the second trimester or iatrogenic preterm delivery due to intrauterine growth restriction, preeclampsia, or abruption.

Cytotrophoblastic cells fuse constantly with the overlying syncytiotrophoblast/syncytium to maintain the function of the trophoblast. Syncytin-1 is the only molecule known to directly induce fusion in the placental trophoblast. Many other proteins, such as gap junctions (e.g., connexin 40) and transcription factors, play a role in the molecular pathways directing the trophoblast turn over. Despite the significance of this process for successful placentation, the mechanisms regulating its activity remain poorly understood.

In this chapter we present several different model systems that can be utilized to investigate the regulation of the cell fusion process in the trophoblast. We describe cell-based assays as well as tissue-related protocols. We show how fusion can be monitored in (1) BeWo cells as a trophoblast cell line model, (2) HEK239 using syncytin-1 as a fusion molecule, and (3) a floating villi explant model. Furthermore, we will present strategies to inhibit fusion in the different models. These techniques represent powerful tools to study the molecular mediators of cell fusion in the trophoblast.

Key Words:

Cell fusion; trophoblast; syncytiotrophoblast; fusion assay; syncytin-1. 


  1. 1.
    Adler, R. R., Ng, A. K., and Rote, N. S. (1995) Monoclonal antiphosphatidylserine antibody inhibits intercellular fusion of the choriocarcinoma line, JAR. Biol. Reprod. 53(4), 905–910.CrossRefPubMedGoogle Scholar
  2. 2.
    Lyden, T. W., Ng, A. K., and Rote, N. S. (1993) Modulation of phosphatidylserine epitope expression by BeWo cells during forskolin treatment. Placenta 14(2), 177–186.CrossRefPubMedGoogle Scholar
  3. 3.
    Drewlo, S., et al. (2006) C-Terminal truncations of syncytin-1 (ERVWE1 envelope) that increase its fusogenicity. Biol. Chem. 387(8), 1113–1120.CrossRefPubMedGoogle Scholar
  4. 4.
    Baczyk, D., et al. (2004) Complex patterns of GCM1 mRNA and protein in villous and extravillous trophoblast cells of the human placenta. Placenta 25(6), 553–559.CrossRefPubMedGoogle Scholar
  5. 5.
    Morrish, D. W., et al. (1987) Epidermal growth factor induces differentiation and secretion of human chorionic gonadotropin and placental lactogen in normal human placenta. J. Clin. Endocrinol. Metab. 65(6), 1282–1290.CrossRefPubMedGoogle Scholar
  6. 6.
    Borges, M., et al. (2003) A two-colour fluorescence assay for the measurement of syncytial fusion between trophoblast-derived cell lines. Placenta 24(10), 959–964.CrossRefPubMedGoogle Scholar
  7. 7.
    Kudo, Y. and Boyd, C. A. (2002) Changes in expression and function of syncytin and its receptor, amino acid transport system B(0) (ASCT2), in human placental choriocarcinoma BeWo cells during syncytialization. Placenta 23(7), 536–541.CrossRefPubMedGoogle Scholar
  8. 8.
    Kudo, Y. and Boyd, C. A. (2002) Human placental amino acid transporter genes: expression and function. Reproduction 124(5), 593–600.CrossRefPubMedGoogle Scholar
  9. 9.
    Mi, S., et al. (2000) Syncytin is a captive retroviral envelope protein involved in human placental morphogenesis. Nature 403(6771), 785–789.CrossRefPubMedGoogle Scholar
  10. 10.
    Baczyk, D., et al. (2006) Bi-potential behavior of cytotrophoblasts in first trimester chorionic villi. Placenta 27(4–5), 367–374.CrossRefPubMedGoogle Scholar
  11. 11.
    Blond J. L., Lavillette D., et al. (2000) 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. 74(7), 3321–3329.CrossRefPubMedGoogle Scholar
  12. 12.
    Chang, C., et al. (2004) Functional characterization of the placental fusogenic membrane protein syncytin. Biol. Reprod. 71(6), 1956–1962.CrossRefPubMedGoogle Scholar
  13. 13.
    Morrish, D. W., et al. (1997) In vitro cultured human term cytotrophoblast: a model for normal primary epithelial cells demonstrating a spontaneous differentiation programme that requires EGF for extensive development of syncytium. Placenta 18(7), 577–585.CrossRefPubMedGoogle Scholar
  14. 14.
    Frendo, J. L., et al. (2003) Direct involvement of HERV-W Env glycoprotein in human trophoblast cell fusion and differentiation. Mol. Cell Biol. 23(10), 3566–3574.CrossRefPubMedGoogle Scholar
  15. 15.
    Lavillette, D., et al. (1998) A proline-rich motif downstream of the receptor binding domain modulates conformation and fusogenicity of murine retroviral envelopes. J. Virol. 72(12), 9955–9965.PubMedGoogle Scholar
  16. 16.
    Huppertz, B., et al. (2003) Hypoxia favours necrotic versus apoptotic shedding of placental syncytiotrophoblast into the maternal circulation. Placenta 24(2–3), 181–190.CrossRefPubMedGoogle Scholar
  17. 17.
    Black, S., et al. (2004) Syncytial fusion of human trophoblast depends on caspase 8. Cell Death Differ. 11(1), 90–98.CrossRefPubMedGoogle Scholar

Copyright information

© Humana Press, a part of Springer Science + Business Media, LLC 2008

Authors and Affiliations

  • Sascha Drewlo
    • 1
  • Dora Baczyk
    • 1
  • Caroline Dunk
    • 1
  • John Kingdom
    • 1
  1. 1.Womens and Infants Health, Samuel Lunenfeld Research Institute, Department of Obstetrics and Gynaecology, Mount Sinai HospitalUniversity of TorontoOntarioCanada

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