Figure 7. Model of calcineurin regulation of Kcnk5b-mediated activation of developmental gene transcription.

Kcnk5b activation results in reduced cytoplasmic K⁺, which is sufficient to induce the transcription of the shh ligand and lef1 transcription factor as well as components of other developmental pathways to induce coordinated allometric growth of the tissues of the fish fin appendage. Scaling information from the body or local tissues in the fin activate calcineurin so that it dephosphorylates Kcnk5b on S345 to reduce its K⁺-channel activity, which results in isometric growth of the fin.