Contact-mediated control of radial migration of corneal epithelial cells

Patients with a heterozygous mutation in the gene encoding the transcription factor, PAX6, have a degenerative corneal opacity associated with failure of normal radial epithelial cell migration across the corneal surface and a reported wound healing defect. This study investigated the guidance mechanisms that drive the directed migration of corneal epithelial cells.

In vivo corneal epithelial wounding was performed in adult wild-type and Pax6(+/-) mice, and the healing migration rates were compared. To investigate the control of the cell migration direction, primary corneal epithelial cells from wild-type and Pax6(+/-) mice were plated on grooved quartz substrates, and alignment relative to the grooves was assayed. A reconstructed corneal culture system was developed in which dissociated wild-type and genetically mutant corneal epithelial cells could be cultured on a de-epithelialized corneal stroma or basement membrane and their migration assayed with time-lapse microscopy.

The Pax6(+/-) cells efficiently re-epithelialized corneal wounds in vivo but had mild slowing of healing migration compared to the wild-type. Cells aligned parallel to quartz grooves in vitro, but the Pax6(+/-) cells were less robustly oriented than the wild-type. In the reconstructed corneal culture system, corneal epithelial cells continued to migrate radially, showing that the cells are guided by contact-mediated cues from the basement membrane. Recombining wild-type and Pax6 mutant corneal epithelial cells with wild-type and Pax6 mutant corneal stroma showed that normal Pax6 dosage was required autonomously in the epithelial cells for directed migration. Integrin-mediated attachment to the substrate, and intracellular PI3Kγ activity, were required for migration. Pharmacological inhibition of cAMP signaling randomized migration tracks in reconstructed corneas.

Striking patterns of centripetal migration of corneal epithelial cells observed in vivo are driven by contact-mediated cues operating through an intracellular cAMP pathway, and failure to read these cues underlies the migration defects that accompany corneal degeneration in patients with mutations in PAX6.