Thyroid hormone-induced differential synthesis of water-insoluble proteins in epidermal cell cultures from the hind limb of Rana catesbeiana tadpoles in stages XII–XV and XVI–XIX

Abstract

Hind limb epidermal cell cultures from stage XII–XV and XVI–XIX tadpoles of the American bullfrog Rana catesbeiana were maintained for 36 and 120 hr in medium containing either fetal calf serum or thyroid hormone (3,3′,5-triiodothyronine, T 3; 3 × 10 −10 mol/ml). T 3 induces the precocious synthesis (within the first 36 hr) of a 59-kDa keratin associated with epidermal stratification in cultures from stages XII–XV. In epidermal cell cultures from stages XVI–XIX, T 3 produces an overall pattern of water-insoluble proteins, including keratins, which is strikingly similar to temporally differentiated cultures (120 hr). A 73-kDa protein is among the water-insoluble proteins precociously synthesized by 36-hr-old cultures from stages XVI–XIX treated with T 3. This protein, which is not immunoprecipitated by antibodies raised against keratins, corresponds in M r and p I to a mammalian differentiation-specific desmosomal plaque protein. Immunoprecipitation of keratins from 120-hr-old cultures shows that many of the water-insoluble proteins synthesized are, indeed, keratins. Further, quantitation, by laser densitometry, of immunoprecipitated keratins from 120-hr cultures demonstrates that greater amounts of keratins, particularly the 65 and 59 kDa which are associated with a differentiated epidermis, are present in stages XVI–XIX. This study indicates that epidermal cell cultures from stages XVI–XIX respond more quickly to the differentiating effects of T 3.