HAIR FOLLICLE HAS A NOVEL ANAGEN-SPECIFIC PROTEIN, MKAP13

To identify the anagen hair follicle-specific proteins, we screened th e cDNA library prepared from the murine skins of anagen phase by the d ifferential hybridization technique. Fifty-four cDNA clones expressed specifically in anagen phase were isolated, and most were found to cor respond to known proteins in the hair follicles. Alternatively, we iso lated a cDNA clone encoding a novel protein that possessed an entire o pen reading frame of 501 base pairs. This protein with a molecular wei ght of 17.9 kDa has no specific motifs nor significant homology to pro teins already reported, although it contains some direct repeats that are often observed in intermediate filament-associated proteins and ha s a similar amino acid composition as a member of them, Northern blot analysis demonstrates that the transcript of this protein is skin spec ific, and that it is present in mid- and late anagen but not in catage n, telogen, and early anagen phases. The transcript appears to be expr essed specifically in the keratogenous zone of the cortical cells of h air follicles, as exhibited by in situ hybridization, Furthermore, imm unohistochemical study confirms that the protein is distributed in the cytoplasms of the keratinizing cortical cells and is undetected in th e completely keratinized ones. These results suggest that this protein can be identified as a new member of intermediate filament-associated proteins and is related to the keratinization of the cortical cell la yer in mouse hair. Therefore, we have termed this novel protein mKAP13 according to the unified nomenclature.