Figure 3.

Schematic diagram of extracellular and cellular process associated with differentiation of mesenchymal cells to osteoblast cells. Undifferentiated mesenchymal cells surrounding the brain express diffusible extracellular molecules, which play a key role in cell differentiation (① and ②). One of the molecules (activator) activates signaling pathways to initiate cell differentiation of mesenchymal cells into osteoblasts (③). In an extracellular process, the activator simultaneously enhances itself (④) and the other key molecule (inhibitor) (⑤), while the inhibitor inhibits the activator (⑥). These two proteins eventually establish a regulatory loop and diffuse in space with different speed (⑦) to form an inhomogeneous spatial pattern of concentration.