British Society for Investigative Dermatology: annual meeting, University of Nottingham, 30 September to 1 October 1983. Abstracts.

Abstract

Epidermal tonofilaments are composed of a complex group of keratins. These major differentiation products are synthesized by living keratinocytes and modified during the formation of mature corneocytes. More detailed study of keratins from different layers of living epidermis has revealed that alterations in keratin expression occur during keratinocyte maturation prior to cornification. Basal, spinous and granular cell fractions of mouse and human epidermis were prepared by trypsin treatment and percoll gradient centrifugation. Keratins were isolated from cytoskeletal preparations of each fraction and from pure statum corneum. These were characterized by one-and two-dimensional (IEF and NEpHGE) electrophoresis and peptide mapping after digestion with V8 protease. Basal cell fractions contained two major keratins (human 59K, 52K; mouse 59K, 54K), the larger of each pair belonging to the basic keratin group (pi 6-5-8-0) and the smaller to the acidic group (pi 5-0-5-5). Spinous cell fractions contained two additional major keratins (human 68K basic, 57K acidic; mouse 67K basic, 57K acidic) and in the granular cell fractions, these two additional keratins became the major components. In each case basic-acidic keratin pairs were present in a 1:1 ratio. Peptide mapping confirmed that the same-sized keratins from the different fractions were identical, all four keratins having unique maps. Corneocytes contained smaller and more acidic keratins (humans 64K, 57K, 55K; mouse 63K, 61K, 57K, 56K) and peptide mapping indicated that these were produced by proteolytic modification of the 67K/68K basic and 57K acidic keratins abundant in the granular layer. We conclude that cells which attain a suprabasal position express two additional keratins which later undergo further modification producing mature corneocyte keratin. The 'basal-cell type' keratins appear to be quantitatively reduced as terminal differentiation progresses.