The temporal and spatial expression of the novel Ca++-binding proteins, Scarf and Scarf2, during development and epidermal differentiation

During the process of epidermal differentiation, intracellular and extracellular calcium (Ca++) concentrations induce an array of signaling pathways [Berridge, M.J., Lipp, P., Bootman, M.D., 2000. The versatility and universality of calcium signaling. Nature Rev. Mol. Cell. Biol. 1, 11-21]. Keratinocytes follow a complex Ca++-dependent program of differentiation moving from the basal proliferative layer, through the spinous and granular differentiated layers to ultimately culminate in the formation of the cornified layer of the epidermis. Members of the Ca++-binding proteins play a central role in the transduction of Ca++ signals. Utilizing a suppressive subtractive hybridization screen comparing basal and differentiated keratinocytes, we identified the novel Ca++-binding protein genes, Scarf (skin Calmodulin-related factor) and Scarf2, which have homology to calmodulin (CaM). In this study, we present a comprehensive analysis of the expression pattern for Scarf and Scarf2 transcripts and proteins in the developing mouse. To examine Scarf2 expression during embryogenesis, we performed in situ hybridization, and detected expression in the hair follicle, skin and nasal epithelium. These results showed substantial overlap with the previously reported Scarf gene expression [Hwang, M., Morasso, M.I., 2003. The novel murine Ca2+-binding protein, Scarf, is differentially expressed during epidermal differentiation. J. Biol. Chem. 278, 47827-47833]. Comparing the expression patterns of Scarf and Scarf2 proteins in neonatal and adult mouse skin with several structural epidermal proteins, i.e. keratin 14 (K14), keratin 1 (K1), loricrin (LOR) and filaggrin (FIL) showed that their expression overlaps K1, an early marker of keratinocyte differentiation. Interestingly, Scarf and Scarf2 were also detected in the tongue and oral epithelia, rib bone undergoing ossification and in the medullar region of thymus.