CONLON, JM*; OHNUMA, A; KAWASAKI, H; IWAMURO, S; UAE University, Al-Ain, United Arab Emirates; Toho University, Chiba, Japan; Toho University, Chiba, Japan; Toho University, Chiba, Japan: Triiodothyronine differentially stimulates expression of genes encoding antimicrobial peptides in the skin of Tago�s brown frog Rana tagoi

For many anurans, the synthesis of polypeptides with a broad spectrum of antimicrobial activity in the granular glands present in the skin is an important feature of their defense strategy against pathogenic microorganisms. Using RT-PCR, two cDNAs encoding preprotemporins were cloned from a total RNA preparation from the skin of Tago�s brown frog Rana tagoi. Preprotemporin-1TGa cDNA directs the synthesis of temporin-1TGa (FLPILGKLLSGIL.NH₂), previously isolated from R. tagoi skin and shown to be active against Gram-positive bacteria. Preprotemporin-1TGb cDNA directs the synthesis of a novel 16 amino-acid-residue peptide (AVDLAKIANKVLSSLF.NH₂) that, atypically for members of the temporin family, inhibits the growth of Gram-negative bacteria more effectively than Gram-positive bacteria. Exposure of the animals to 10^-8M triiodothyronine (T₃) for 72 h enhanced expression of the preprotemporin-1TGb gene (approx. 3-fold) but did not change the level of expression of the preprotemporin-1TGa gene. Exposure of the animals to 10^-8M T₃ and 10^-6M bisphenol A, an endocrine disrupting chemical that potently inhibits the action of thyroid hormones, reduced expression of the preprotemporin-1TGb gene by 10-fold and the preprotemporin-1TGa gene by 3-fold. We propose that T₃-stimulated synthesis of antimicrobial peptides is important in protecting the animal against microorganisms, particularly at metamorphosis and during skin molting, but environmental pollutants can inhibit peptide synthesis and render the animal susceptible to invasion by pathogens.