Meeting Abstract
To study the effects of thyroid hormones (TH) on frog metamorphosis, researchers often apply TH to tadpoles to induce metamorphosis precociously. However, precociously induced remodeling might not resemble natural remodeling because remodeling might be induced before larval tissues are fully competent to respond to TH or before they attain the shapes at which natural remodeling starts. Also, remodeling induced in young tadpoles occurs during a period of exceptionally fast growth, and fixed concentrations of T3 or T4 are unlikely to have the same effects as the changing T3 and T4 levels in natural metamorphosis. This study aims to clarify how precociously induced remodeling affects the size and shape changes in two pharyngeal arch cartilages, Meckel’s cartilage (MC) and ceratohyal (CH). Xenopus tadpoles were pretreated at early, mid and late tadpole and early metamorphic stages with 1 mM methimazol to arrest them at different starting stages (NF 46, 53, 57 and 59/60). The tadpoles were subsequently treated with 0, 1, 5, 10, or 50 nM T3 or T4 as well as 1 mM methimazol and 10 uM iopanoic acid, which prevent the tadpoles from making their own TH and converting T3 or T4 into another form of TH. Specimens were photographed before and after treatments and then fixed and stained for cartilage and bone. The MC and CH were dissected out and photographed, and the photographs were landmarked and digitized to calculate final dimensions. Initial dimensions were estimated from start photographs using equations from a previous study of untreated individuals that relate external to internal dimensions. The shape changes induced at NF 46 are significantly different from natural metamorphosis due to early tadpole growth, T4 has different effects from T3, and though changes induced at higher stages are more like natural remodeling, some produce abnormalities.
