The Xenopus embryonic epidermis is a mucociliary epithelium - analogous to that found in mammalian airways. This tissue is characterised by the presence of multiciliated cells (MCCs) and goblet cells. A third cell type, the ion-secreting cell, was recently discovered in the Xenopus epidermis. Two papers now identify a final cell type in the frog embryonic skin, the small secretory cell (SSC). Eamon Dubaissi and colleagues () show that SSCs are specified by the transcription factor Foxa1, are characterised by the presence of large secretory vesicles containing mucin-like (glycosylated) proteins and are important for immune defence: tadpoles lacking SSCs die from bacterial infection. Axel Schweickert and co-workers () find that these cells also secrete serotonin and provide evidence for serotonin-mediated regulation of ciliary beat frequency in MCCs, as in other systems. Given the value of the Xenopus epidermis as a model for mucociliary epithelia and disease, the identification of SSCs provides important insights into the nature and function of this epithelium.
