Functional analysis of keratin components in the mouse hair follicle inner root sheath

BACKGROUND: Recently, a family of novel type I keratins of the inner root sheath of the hair follicle were discovered, increasing the number of keratins known to be expressed in the hair follicle. The mouse database shows three keratins that are possible orthologues of these inner root sheath keratins. The sequences of these keratins include rather unusual changes to a highly conserved motif at the end of the alpha-helical rod domain of the proteins, thought to be important in filament assembly. OBJECTIVES: To investigate whether these keratins are expressed in the inner root sheath and to determine whether they assemble normally. METHODS: To investigate this, polyclonal antibodies were raised for immunolocalization of the keratins and their cDNAs were cloned for transfection into cultured cells. RESULTS: At least two of these keratins were expressed in the inner root sheath but the timing of expression of the different keratins was variable. Transfection of the relevant cDNAs into cells in culture indicated that these keratins were capable of integrating into existing keratin networks without disruption, but that de novo filament assembly with the type II inner root sheath keratin, mK6irs, was poor. CONCLUSIONS: These results provide further evidence of the complexity of keratin expression in the three concentric layers of the inner root sheath.