The analysis of the expression of a novel gene, Xenopus polka dots, which was expressed in the embryonic and larval epidermis during early development

The epidermis serves as a barrier protecting organs and tissues from the environment, and comprises many types of cells. A cell renewal system is established in epidermis: old epithelial cells are replaced by newly differentiated cells, which are derived from epidermal stem cells located near basement membrane. In order to examine the mechanism of epidermal development, we isolated a novel gene expressed in Xenopus epidermis and named the gene Xenopus polka dots (Xpod) from its polka dot-like expression pattern throughout larval periods. Several immunohistochemical examinations showed that the Xpod-expressing cell type is neither p63-positive epidermal stem cells, nor the α-tubulin-positive ciliated cells, but a subset of the foxi1e-positive ionocytes. The forced gene expression of foxi1e caused the suppression of Xpod expression, while Xpod showed no effect on foxi1e expression. In a comparison of several osmotic conditions, we found that hypertonic culture caused the increase in number of the Xpod-expressing cell, whereas number of the foxi1e-expressing cells was reduced under the hypertonic condition. These results show the possibility that Xpod is involved in the establishment of a certain subpopulation of ionocytes under hypertonic conditions.