Expression of Syncytin 1 (HERV-W), in the preimplantation human blastocyst, embryonic stem cells and trophoblast cells derived in vitro

Abstract

Studyquestion: As Syncytin 1 (human endogenous retrovirus (HERV-W)) is crucial for human embryo placentation is it expressed during preimplantation embryo development? summaryanswer: Syncytin 1was expressed mainly in trophoblast cells of the blastocyst particularly in cells underlying the inner cell mass (ICM). what is known already: Syncytin 1 (along with HERV-FRD or Syncytin 2) is expressed in first-trimester placenta and required for cell-cell fusion to enable formation of syncytiotrophoblast and effective placentation. study design, size and duration: Preimplantation human embryos donated for research were cultured in vitro and protein expression of Syncytin 1 at the blastocyst stage of development investigated. Comparisons were made with protein (Syncytin 1) and mRNA (Syncytin 1and 2) expression inhumanembryonic stemcells (hESCs) under going differentiation to trophoblast-like cells in vitro. In total,10blastocysts (×3 or 4 replicates) were analysed and 4 hESC lines. The study was terminated after consistent observations of embryos were made. participants/materials, setting, methods: Donated embryos were thawed and cultured to blastocyst, fixed with 4% w/v paraformaldehyde. Syncytin 1 protein expressionwas determined by immunofluorescent localisation and confocalmicroscopy. Additionally, hESCs were differentiated to trophoblast-like cells in standard and conditioned culturemediumwith growth factors (bonemorphogenetic protein 4 (BMP4) or fibroblast growth factor 4 (FGF4) and assessed for mRNA (Syncytin 1 and 2) by quantitative polymerase chain reaction (qPCR) and protein expression by immunolocalization and western blot. main results and role of chance: Syncytin 1 was expressed in cytoplasm and on the cell surface of some trophoblast cells, and consistently the trophectodermunderlying the ICMof the blastocyst.Therewasweak butconsistent expression of Syncytin 1 in cells onthe periphery of the ICMalso displaying pluripotency antibody marker (Tra-1-60). Three-dimensional reconstruction of confocal slice data provided good visualization of expression. The time course of expression of Syncytin 1was replicated in hESCs differentiated in vitro confirming the embryo observations and providing statistically significant differences in protein and mRNA level (P= 0.002) and (P < 0.05), respectively. limitation, reasons for caution: Culture of a limited number of embryos to blastocyst in vitro may not replicate the range and quality of development in situ. Probes (antibodies, PCR) were tested for specificity, but might have non-specific reactions. wider implications of findings: Syncytin expression is a prerequisite for embryo implantation and placentation. Understanding when expression first occurs during embryo development may be informative for understanding conditions of abnormal gestations such as pre-clampsia. study funding/competing interests: The studywas supported partly by an ERASMUS training grant and grantG0801059 from the Medical Research Council, U.K. There were no competing interests.