Part I: Substances Secreted by the Preimplantation Human Embryo

Human preimplantation embryos secrete a number of soluble factors into their environment, be it in vivo or in vitro. In vivo, these signals are fundamental for survival and implantation of the blastocysts. In vitro, during an assisted reproduction treatment, embryo-derived signals may be detected in the conditioned culture media and might serve for the estimation of embryo quality and its capacity to implant. Furthermore, the same fundamental soluble factors may be added to preimplantation embryo culture media or instilled into the uterus during embryo transfer. Several molecules have been detected in conditioned embryo media. The available literature about the most prominent factors, HLA-G, interleukins, hCG, PAF, leptin, SP-1, EPF, and Wnt beta catenin, are reviewed in this article. Several published results are contradictory or are based on doubtful analyses, which detect protein concentrations in the media which exceed the weight of the entire blastocyst. This review discloses the littleness of the current knowledge about the human embryo secretome, the difficulties of analyses and the need of further investigation.

Keywords: Preimplantation embryos, HLA-G, interleukins, hCG, PAF, leptin, SP-1, EPF, Wnt beta catenin.