Stem Cell-Based Embryo Models: En Route to a Programmable Future

Engineering a computable epiblast for in silico modeling of developmental toxicity

Developmental hazard evaluation is an important part of assessing chemical risks during pregnancy. Toxicological outcomes from prenatal testing in pregnant animals result from complex chemical-biological interactions, and while New Approach Methods (NAMs) based on in vitro bioactivity profiles of human cells offer promising alternatives to animal testing, most of these assays lack cellular positional information, physical constraints, and regional organization of the intact embryo. Here, we engineered a fully computable model of the embryonic disc in the CompuCell3D.org modeling environment to simulate epithelial-mesenchymal transition (EMT) of epiblast cells and self-organization of mesodermal domains (chordamesoderm, paraxial, lateral plate, posterior/extraembryonic). Mesodermal fate is modeled by synthetic activity of the BMP4-NODAL-WNT signaling axis. Cell position in the epiblast determines timing with respect to EMT for 988 computational cells in the computer model. An autonomous homeobox (Hox) clock hidden in the epiblast is driven by WNT-FGF4-CDX signaling. Executing the model renders a quantitative cell-level computation of mesodermal fate and consequences of perturbation based on known biology. For example, synthetic perturbation of the control network rendered altered phenotypes (cybermorphs) mirroring some aspects of experimental mouse embryology, with electronic knockouts, under-activation (hypermorphs) or over-activation (hypermorphs) particularly affecting the size and specification of the posterior mesoderm. This foundational model is trained on embryology but capable of performing a wide variety of toxicological tasks conversing through anatomical simulation to integrate in vitro chemical bioactivity data with known embryology. It is amenable to quantitative simulation for probabilistic prediction of early developmental toxicity.

Cell Transdifferentiation: A Challenging Strategy with Great Potential

With the discovery and development of somatic cell nuclear transfer, cell fusion, and induced pluripotent stem cells, cell transdifferentiation research has presented unique advantages and stimulated a heated discussion worldwide. Cell transdifferentiation is a phenomenon by which a cell changes its lineage and acquires the phenotype of other cell types when exposed to certain conditions. Indeed, many adult stem cells and differentiated cells were reported to change their phenotype and transform into other lineages. This article reviews the differentiation of stem cells and classification of transdifferentiation, as well as the advantages, challenges, and prospects of cell transdifferentiation. This review discusses new research directions and the main challenges in the use of transdifferentiation in human cells and molecular replacement therapy. Overall, such knowledge is expected to provide a deep understanding of cell fate and regulation, which can change through differentiation, dedifferentiation, and transdifferentiation, with multiple applications.

Building a baby: are stem cell-based, embryo-like models the key to unlocking the secrets of human development?

Developments in stem-cell technology have presented researchers with a powerful method with which to examine why things go wrong in early embryonic development, yet with this advance in research ability comes a polarizing ethical dilemma.