Led by Professor Magdalena Zernicka-Goetz from the California Institute of Technology and the University of Cambridge, the study aimed to enhance our understanding of pre-implantation human development. Noting that 70 percent of IVF implantations fail, the researchers tracked the differentiation of cells labelled at the two-cell stage to determine any bias in their contributions.
Professor Zernicka-Goetz, whose study was published in Cell, expressed her longstanding interest in cellular fate decisions. Pre-implantation development, which spans from fertilization to implantation around day seven, is critical for IVF success. During this period, the embryo, starting as a single zygote, undergoes a series of divisions and differentiates into a few hundred cells by the time of implantation. These cells are categorized into three types: those forming the placenta, the embryo, and the yolk sac.
Initially, the zygote divides into two cells, which continue to divide into four, eight, and so on. These early cells are considered equal and totipotent, capable of generating all cell types. Differentiation begins at the 8-16 cell stage, with outer cells becoming placenta precursors and inner cells forming the embryo and yolk sac.
Using green fluorescent protein, the researchers labelled one of the two cells to track its descendants. They found that one cell is truly totipotent, contributing to both body and placenta, while the other mainly forms the placenta. This research marks the first detailed cell tracking in early-stage human embryos.
Professor Nicolas Plachta of the University of Pennsylvania, who was not involved in the study, praised the cell tracking efforts. Despite the rarity of obtaining donated embryos at the zygote stage, the researchers utilized time-lapse imaging from IVF clinics to monitor embryo development, underscoring the importance of collaboration between researchers and clinics. This improved understanding of early embryo development could lead to better strategies for addressing IVF implantation failures.
