Corneal goblet cells and their niche: implications for corneal stem cell deficiency.

Goblet cells are terminally differentiated cells secreting mucins and antibacterial peptides that play an important role in maintaining the health of the cornea. In corneal stem cell deficiency, the progenitor cells giving rise to goblet cells on the cornea are presumed to arise from differentiation of cells that migrate onto the cornea from the neighboring conjunctiva. This occurs in response to the inability of corneal epithelial progenitor cells at the limbus to maintain an intact corneal epithelium. This study characterizes clusters of cells we refer to as compound niches at the limbal:corneal border in the unwounded mouse. Compound niches are identified by high expression of simple epithelial keratin 8 (K8) and 19 (K19). They contain variable numbers of cells in one of several differentiation states: slow-cycling corneal progenitor cells, proliferating cells, nonproliferating cells, and postmitotic differentiated K12+Muc5ac+ goblet cells. Expression of K12 differentiates these goblet cells from those in the conjunctival epithelium and suggests that corneal epithelial progenitor cells give rise to both corneal epithelial and goblet cells. After wounds that remove corneal epithelial cells near the limbus, compound niches migrate from the limbal:corneal border onto the cornea where K8+ cells proliferate and goblet cells increase in number. By contrast, no migration of goblet cells from the bulbar conjunctiva onto the cornea is observed. This study is the first description of compound niches and corneal goblet cells and demonstration of a role for these cells in the pathology typically associated with corneal stem cell deficiency.