Embryonic development requires cells to become different from each other. The dominant view over the past few decades has been that cells become different because they are instructed to do so. A cell adopts a particular role because is receives a signal and responds accordingly. A neighbouring cell does not receive the signal and so adopts a different role. It is simple and attractive to imagine cells behaving as they are told. However a counter view, that cells make their own decisions, has recently resurfaced.
In an advanced review published in WIREs Developmental Biology, Jonathan Chubb illuminates the perspective of single cell decision-making during development, by taking us through the key conceptual and experimental battlegrounds, from differentiation in bacteria, through to recent work on stem cell differentiation. He places specific emphasis on the proposed role of unpredictable gene expression in providing the initial differences between cells that are then amplified to produce different mature cell types. Gene expression is inherently unpredictable, in all forms of life and a popular hypothesis has been that this unpredictability is functional, allowing cells to become different without being told to by some instructive event. Chubb views this hypothesis from several perspectives, from attempts to understand how unpredictable gene expression arises, to experimental approaches to monitor gene expression in individual cells over developmental transitions, through to experimental perturbations required to evaluate the importance of unpredictable expression for specific regulators. He also discusses how some developmental systems have evolved to make gene expression more predictable, to ensure that cells adopt the correct roles at the correct position in the embryo.
Text contributed by Jonathan Chubb