In general, cells in one region of an embryo synthesize and secrete proteins that determine the path of differentiation of cells nearby. In several cases, cells are now known to activate different genes according to the concentration of a single signalling molecule, which is therefore described as a morphogen. Activin is a candidate for the natural inducer of mesodermal differentiation which takes place a few hours after fertilization.
Cells respond to activin by transcribing various mesodermal genes in a concentration-dependent way.
We find that they do this by measuring the absolute number of activin-occupied receptors of one type. Our overall aim is to understand the mechanism of concentration-dependent signalling between cells in development. In addition to analysing how cells measure the concentration of an external signalling factor, we determine how signals are transduced quantitatively through the cytoplasm to the nucleus. To understand how embryonic cells are made to differentiate may help, eventually, to reveal ways of redirecting cancer cells from uncontrolled proliferation to a differentiated state. Eomes is expressed in the cells between the beads and the Xbra ripple.