Changing patterns of incorporation of (14C)histidine and (3H)leucine into epidermal proteins during differentiation of fetal rat skin

Abstract

Synthesis of epidermal proteins has been assessed during epidermal differentiation in fetal rat skin by studies of the simultaneous incorporation of [14C]histidine (H) and [3H]leucine (L) in vitro. Relative incorporation of the two amino acids into epidermal proteins was assessed in terms of H/L ratios and absolute rates of incorporation related to DNA content. Biochemical parameters were correlated with morphologic development. An increase in incorporation of both amino acids accompanied stratification and development of granular and cornified layers between 18 days of gestation and 3 to 5 days postpartum. Relatively greater incorporation of histidine after development of mature granular cells and stratum corneum was reflected in increasing H/L ratios. These results correlated with negative Pauly staining of the initial fetal keratohyaline granules at day 18 and positive staining of mature granules at subsequent stages of development. H/L ratios appear to represent a sensitive marker for differential protein synthesis during differentiation in whole epidermis. The results suggest that biosynthesis of histidine-rich protein is associated with production of mature keratohyaline granules during fetal development.