REGION-SPECIFIC PATTERNS OF BETA KERATIN EXPRESSION DURING AVIAN SKINDEVELOPMENT

The transient embryonic layers primarily composed of a periderm and su bperiderm cover most regions of the chick embryo and are the first sup rabasal cell layers covering the body ectoderm. This study presents ev idence for regional variation in the expression of beta keratin in the embryonic layers. Here we show that the embryonic layers covering the anterior metatarsal region of the chicken hindlimb (scutate scale for ming region) produce several members of the beta keratin family of pol ypeptides, designated beta (beta) 1-7. These specific polypeptides are later expressed in this region exclusively in the thick, cornified be ta strata of mature scutate scales. In contrast to this sequence of ev ents, the embryonic layers overlying the epidermis of the ventral foot pad (reticulate scale-forming region) and those covering the epidermi s in apteric regions of the body produce beta keratin polypeptides bet a1-3 and beta2,3, respectively, but no subsequent expression of these proteins occurs in the mature epidermises of these regions. Furthermor e, we find that the embryonic layers of the skin overlying the anterio r metatarsal region of birds homozygous for the mutation ''scaleless'' (sc/sc), which completely lack scutate scales, produce the same membe rs of the beta keratin family, beta1-7, as the embryonic layers and be ta strata of normal scutate scales. Thus, the accumulation of specific beta keratin polypeptides in the developing anterior metatarsal regio n appears to occur in two distinct phases; first, an early region-spec ific expression in cells of the embryonic layers followed by a second phase of expression which occurs in conjunction with appendage morphog enesis. The relationship between differentiation of embryonic skin and the expression of beta keratins is discussed. (C) 1993 Wiley-Liss, In c.