Figure 2.

Regional Specification and the Role of Noise

(A) Layout of key functional areas in the mouse cortex (O'Leary et al., 2007). V1, primary visual cortex; A1, primary auditory cortex; S1, primary somatosensory cortex; F/M, frontal/motor cortex.

(B) Some of the molecular gradients that play a role in specifying areal identity in mouse cortex during development.

(C) One of the networks of interactions between signaling molecules in the model of Giacomantonio and Goodhill (2010) that generated arealization patterns most consistent with the experimental data. Shaded and unshaded labels indicate genes and proteins, respectively.

(D) Schematic of three sources of noise that constrain concentration measurement by a cell.

(E) Specification of boundaries in the developing zebrafish hindbrain by a gradient of retinoic acid. Top: schematic representation of the retinoid acid gradient. Any such gradient can only provide noisy information. Bottom: experimental image showing that by 12 hr postfertilization this gradient has nevertheless helped to specify sharply defined borders of the expression of krox20 (green) and hoxb1a (red). Adapted from Zhang et al. (2012).