A new look into an old problem: keratins as tools to investigate determination, morphogenesis, and differentiation in skin.

Abstract

We have investigated keratin and keratin mRNA expression during (1) differentiation of stem cells into epidermis and hair follicles and (2) morphogenesis of follicles. Our results indicate that a type I keratin K14 is expressed early in embryonal basal cells. Subsequently, its expression is elevated in the basal layer of developing epidermis but suppressed in developing matrix cells. This difference represents an early and major biochemical distinction between the two diverging cell types. Moreover, because expression of this keratin is not readily influenced by extracellular regulators or cell culture, it suggests a well-defined and narrow window of development during which an irreversible divergence in basal and matrix cells may take place. In contrast to KI4, which is expressed very early in development and coincident with basal epidermal differentiation, a hairspecific type I keratin and its mRNA is expressed late in hair matrix development and well after follicle morphogenesis. Besides providing an additional developmental difference between epidermal and hair matrix cells, the hair-specific keratins provide the first demonstration that keratin expression may be a consequence rather than a cause of cell organization and differentiation.[Key Words: Hair-specific keratins; keratin mRNA expression; hair follicle morphogenesis]

The Role of the Hairless (hr) Gene in the. Regulation of Hair Follicle Catagen Transformation

“…This widening starts from the most distal (adjacent to the epidermis) region of the suprainfundibular ORS (Figure 3A), which exhibits an epidermal type of keratinization. 34 This may reflect hr mutation-related abnormalities in the interfollicular epidermis rather than in the HF itself, which actually displays normal morphological features at that time. hr mRNA expression has been reported not only in the HF, but also in the interfollicular epidermis 12 .…”

Galectin‐3 is expressed in the notochord, developing bones, and skin of the postimplantation mouse embryo

“…They stay fused until 6 days after birth, when a final separation occurs. There are also extensive epitheliaVmesenchyma1 transitions occurring in and around the whisker follicles at this time (Kopan and Fuchs, 1989) and galectin-3 may contribute to the "de-adhesiveness" necessary for this process. In support of this notion, galectins have been shown to "block off" glycoconjugates on the substratum to which cells normally adhere, allowing cells to become free to move away from anchorage points in the substratum.…”

Expression of keratin K14 in the epidermis and hair follicle: insights into complex programs of differentiation.

“…However, it is not known whether the temporal and spatial expression of K5 and K14 in the ORS is similar to that of epidermis, and moreover, it is controversial whether matrix cells truly contain K14: the only antibody which has detected K14 in matrix is an mAb (KA1) whose antigenic specificity has not yet been fully analyzed (Nagle et al, 1984(Nagle et al, , 1986. That this antibody has not yet been well characterized becomes an especially important issue in light of findings by other researchers that (a) common antigenic epitopes exist between keratins and nonkeratin proteins in hair (Lynch et al, 1986) and (b) other K14-and K5-specific probes have not detected these or other keratins in matrix cells (Moll et al,, 1982b;Heid et al, 1986;Lynch et al, 1986;Kopan and Fuchs, 1989). Hence the extent to which the mitotically active cells of the follicle are truly biochemically similar to epidermal basal cells remains to be determined.…”

“…basal epidermal cells. It is known, for example, that ORS cells express K5 and K14 (Moll et al, 1982b;Lynch et al, 1986;Stark et ai., 1987;Heid et al, 1988aHeid et al, , 1988bMoll et al, 1988;Kopan and Fuchs, 1989), and recently it was claimed that matrix cells also express K14 (Heid et al, 1988a(Heid et al, , 1988bMoll et al, 1988). However, it is not known whether the temporal and spatial expression of K5 and K14 in the ORS is similar to that of epidermis, and moreover, it is controversial whether matrix cells truly contain K14: the only antibody which has detected K14 in matrix is an mAb (KA1) whose antigenic specificity has not yet been fully analyzed (Nagle et al, 1984(Nagle et al, , 1986.…”