FIGURE 14.

A hypothetical model depicting establishment and tandem duplication of anterior–posterior gradients of positional information in the ciliate cell cortex. (A) Hypothetical packages of “cortical morphogen” (CMPs) are synthesized and diffuse out to the cell cortex. (B) CMPs are loaded onto the exposed basal microtubule tracks, where plus‐end or minus‐end directed motors transport them towards the cell's anterior or posterior poles respectively. (C) CMPs become more concentrated in the anterior and posterior poles of the cell depending on their motor‐protein orientations. (D) If such vesicles up‐load and off‐load stochastically, and dock to deliver their contents at the cell surface (where lateral diffusion is limited), one would expect monotonic gradients of anterior morphogen (pink), highest at the cell anterior, and posterior‐morphogen (turquoise) highest at the cell posterior. (E, F) Disrupting morphogen transport at midbody would create two “high‐point” destinations for each class of CMP, one at the cell's original pole, and a second at midbody