Dynamic aspects of protein deimination in developing mouse epidermis

The cornified layer of mammalian epidermis contains deiminated keratins and filaggrin whose arginine residues are partly converted to citrulline residues by peptidylarginine deiminase (EC 3.5.3.15). We have attempted to study dynamic aspects of protein deimination using late embryonic to early postnatal mouse skin. The epidermis was separated from the dermis by brief immersion of skin into a weakly alkaline ammonium chloride solution. The total homogenate of the epidermis was subjected to western blotting analyses for quantitative densitometry of major keratins, deiminated proteins and immunoreactive filaggrin. We found marked increases in both deiminated keratins and deiminated filaggrin from the 18th day of gestation to 2 h after birth followed by rapid decreases to minimum levels at 6 h and subsequent gradual increases surpassing the earlier levels by 72 h after birth. Such variations were associated with consistent changes of the intensity of deiminated proteins stained immunocytochemically. These results suggest that the protein deimination might play a role in dealing with the drastic environmental change after birth. Furthermore, we found compartmentalization of both total and deiminated filaggrins into soluble and particulate fractions. The soluble compartment contained relatively more deiminated filaggrin than the particulate fraction.