This study has documented the major types of lineage progenitor cells at the second level of cell differentiation after the establishment of the primary germ layers in ectopic human embryos in vivo. These correspond to stages 8 and 9 of embryogenesis (weeks 3-4) in the Carnegie collection. The aim of this study was to provide images of fine structure of tissue progenitor cells to compare them with current imaging of their equivalent stem cells identified using fluorescent stem cell markers. These include neural, mesenchymal, endodermal, ectodermal (epidermal) and haematopoietic progenitor cells, including those for amniotic, yolk sac and chorionic tissues that are used in current stem cell research. Neural induction by the notochord has been imaged. This study should give valuable clues to understand the pattern of cell differentiation of embryonic stem cells (ESC) in vitro, which are more or less mimicked in ESC colonies, embryoid bodies and neurospheres as documented in the literature. The fine structure of week-3 and week-4 human ectopic embryos is presented to demonstrate progenitor tissue cells that will eventually form the brain, spinal cord, skin, gut, heart, blood, muscle, bone and other tissues of the human body later on in development. These images should help stem cell researchers using fluorescent markers and other techniques to identify embryonic and adult stem cells in culture.
Sathananthan, A. H., Selvaraj, K., & Clark, J. M. (2012). Fine structure of progenitor cells in early ectopic human embryos. Reproductive BioMedicine Online, 25(3), 315 - 321. https://doi.org/10.1016/j.rbmo.2012.05.008