Meeting Abstract

P1.159  Saturday, Jan. 4 15:30  Isolating the effects of T4 and T3 on cartilage growth and cartilage shape change in Xenopus tadpoles ROSE, C.S.*; CAHILL, J.W.; James Madison Univ., Harrisonburg, Va; James Madison Univ., Harrisonburg, Va rosecs@jmu.edu

Experimental investigations of how thyroid hormone (TH) regulates metamorphic remodeling in Xenopus at the molecular and cellular levels commonly apply TH to induce metamorphic changes in tadpole-stage specimens. Studies in salamanders indicate that the precociously induced remodeling of skeletal tissues can vary in stage- and dose-dependent ways and does not always resemble skeletal remodeling in natural metamorphosis. This study aims to quantify the stage-dependency of size and shape changes induced in two pharyngeal arch cartilages (Meckels cartilage or MC and ceratohyal or CH) by the two different forms of TH (T4 and T3). We treated Xenopus tadpoles at early and late tadpole and early metamorphic stages (NF 46, 57 and 59/60) with 50 nM of either T4 or T3 and compared the effects on body size and size and shape of the two cartilages to the changes that occurred in controls and in natural metamorphosis. TH-treated and control specimens were first pretreated with methimazole to arrest them at the three starting stages, and methimazole and iopanoic acid were applied during the TH treatments to block endogenous TH production and prevent the conversion of T4 and T3 to other forms of TH. Animals were photographed before and after treatments, cleared and stained for cartilage and bone, and their MC and CH dissected and photographed. Body size and cartilage size and shape were quantified from landmarked photographs. The induced size and shape changes differed with stage of induction and type of TH and only those changes induced at NF 59/60 closely resembled natural remodeling. The discrepancy between T3 and T4 effects was most pronounced at NF 46 and resulted from T3 inducing cartilage shape change at the expense of cartilage growth