Single-cell “trajectories” shed light on gene regulation. (A) An idealized regulatory network consisting of two genes can have three distinct stable states. If the ratio of A to B is sufficiently high, the system will fall into a state in which only A is expressed (green region). Likewise, cells expressing predominantly B will eventually express only B. However, cells with roughly equal expression of A and B will remain in a “poised” state (blue) region. The shaded areas are referred to as “basins of attraction,” which determine where cells at different initial positions (white circles) will ultimately rest at equilibrium. (B) Gene expression profiles for individual differentiating cells can be informatically organized into trajectories, potentially revealing regulatory network structure and cell fate dynamics.
