Expression of calcyclin, a calcium-binding protein, in the keratogenous region of growing hair follicles.

Changes in calcium levels control the differentiation of skin epithelial cells and thus may also affect the epithelial cells of the hair follicle. We have isolated a murine cDNA clone, pCAL-F559, for the calcium-binding protein calcyclin by differential screening of a cDNA library made from RNA isolated from hair follicles of 6-d-old mice. The identity of our cDNA clone was established by comparing the DNA sequence with the sequence of the human calcyclin gene. That the authentic calcyclin mRNA encoded by pCAL-559 is present in skin of 3-d-old mice was confirmed by S1 nuclease protection assays. As measured by RNA dot blots, calcyclin mRNA levels in the skin change in accordance with the hair cycle and reaches a peak a few days prior to the mRNA for structural hair proteins. Although we can demonstrate by in situ hybridization that mRNA for calcyclin is localized in the post-mitotic keratogenous region of the hair follicle we can only assume that this calcium binding protein is involved in the control of differentiation of these cells by regulating their Ca++ levels.