SPRR1 gene induction and barrier formation occur as coordinated moving fronts in terminally differentiating epithelia

Stratified, terminally differentiated epithelia, such as epidermis and oral epithelia, provide protective barriers against the environment. We recently developed wholemount assays that demonstrate epidermal barrier function during late gestation and showed that epidermal barrier forms at specific sites (epidermal initiation sites), and then spreads around the body as apparent moving fronts. We now ask if this is a fundamental and widespread mode of epithelial developmental change. If so, then the pattern should be apparent when assaying for developmental change other than barrier institution (e.g., gene induction) and similar types of patterned change should be apparent in other types of epithelia. In this study we demonstrate patterned barrier function in a range of additional stratified epithelia from the oral cavity and show that the gene induction pattern of a stratum corneum precursor small proline-rich region protein 1 (SPRR1) precedes barrier function and occurs in the barrier pattern, i.e., gene induction occurs first at initiation sites and propagates across epithelia as apparent moving fronts. These results demonstrate that late gestational developmental change in multiple terminally differentiating epithelia occurs via initiation sites and moving fronts. The pattern precedes barrier formation and results in a developmental gradient that influences gene induction.