Fig. 9

Biochemical and bioelectric signals guiding directed mesenchyme cell migration in feather. SHH and WNT7A protein produced in the epithelium diffuse into the underlying mesenchyme to induce the SHH and WNT-responding zone, respectively. Together they activate Connexin-43 expression to compose intercellular gap junction channels. Heterogeneously distributed VGCCs and CRAC channels contributed to the inward current observed at posterior–distal part of elongating feathers, while activation of Ca²⁺ -activated K⁺ channels may contribute to the outward current at anterior-basal part of feathers. The gap junction network establishes a low-resistance electrical path across feather mesenchyme, homogenizing differential Ca²⁺ channel activities among cells to allow synchronized Ca²⁺ oscillations to form. These slow oscillations coordinate the collective migration of mesenchymal cells. Meanwhile much faster Ca²⁺ transients occur sporadically in individual cells