Altered keratin biosynthesis follows inhibition of scale morphogenesis by hydrocortisone

Hydrocortisone, administered onto the chorioallantoic membrane (CAM) of 7- to 10-day-old chick embryos, inhibits scale development, in a dose- and stage-dependent manner. The response is also region specific in that hydrocortisone treatment, at a specific dose and time, will completely block scutellate and interstitial scale development while leaving other scale types unaffected. Using histological, biochemical, and immunofluorescence techniques, we have shown that inhibition of scutellate scale morphogenesis prevents the subsequent formation of a beta stratum and alters expression of the alpha keratins. These data support the hypotheses that each avian scale type has its own distinctive temporal, morphological, and biochemical pattern of development; and in the case of scutellate scale development, hydrocortisone treatment alters keratin biosynthesis by interfering with earlier steps in morphogenesis.