Figure 1.

Schematic representation of normal developmental and wound-induced eyespot formation. (A) The first signs of eyespot specification are observed at the last larval stage with the detection of focus-specific gene expression (light blue circle represents the focus cells). At early pupal stages, signalling molecules are expressed in the focus, from where they spread to neighbouring cells, creating a gradient with higher levels close to the source (arrows represent the diffusing signal). As a response to different concentrations of the signal, the focus and cells surrounding it activate the expression of different transcription factors (represented by different coloured rings around the focus). The area where a transcription factor is expressed depends on the sensitivity of its cis-regulatory elements to the morphogen signal activating it and on the possible cross-regulatory interactions between the various transcription factors expressed in the eyespot. These transcription factors will finally activate different pigments generating the adult colour pattern. (B) In the absence of larval specification, wound-healing activated signals can induce expression of the transcription factors activating pigmentation. Thus, two distinct pathways can achieve the same morphological outcome, allowing freedom to co-opt different genes while conserving the same final output.