Embryonic differentiation waves

Richard Gordon (theoretical biologist) and Natalie Gordon proposed that there is a mechanically sensitive bistable organelle in the apical ends of cells in cell sheets about to differentiate (that are competent) and they are under mechanical tension. Depending on where the cell is on the sheet, the tension will be resolved by either the apical end contracting or the apical end expanding. This will result in a biomechanical transduction signal from the cytoskeleton that is passed on to the nucleus which then changes gene expression. If the cell has experienced contraction, one signal is sent and it the cell has experienced expansion then another signal is sent. The signal is the determination of cell fate and is done by the cytoskeleton. They have outlined their research and their theory of differentiation waves in detail in their book *"Embryogenesis Explained"*. For example, the first differentiation takes place during mammalian compaction. Cells on the outside of the cell ball expand and become determined to be trophoblast, cells on the inside contract and become determined to be the inner cell mass. All the other activity, such as changes in gene expression, signalling proteins, release of morphogens, and epigenetic changes, are considered the result of differentiation after the cytoskeleton determines cell fate with purely mechanical signals.