Meeting Abstract
P1.45 Thursday, Jan. 3 A cell and molecular description of early limb development in frogs FOSTER, J.*; KENNEDY, M.; ROSE, C.; James Madison University; James Madison University; James Madison University rosecs@jmu.edu
Frogs differ from other tetrapods in three aspects of limb development. Their limbs develop postembryonically, most or all of limb development is mediated hormonally, and the rate is strongly modulated by environmental factors. Understanding the developmental basis of these features will shed light on how frog evolved their unique life histories and how plasticity in the size and age of frog metamorphosis is induced. We lack a comprehensive description of the cell and molecular biology of limb bud development in frogs. Also, the evidence for when limb development comes under hormonal control remains inconclusive. To begin to address these problems, we are documenting the expression of cell behaviors and genes that contribute to limb patterning, morphogenesis, and thyroid hormone (TH) mediation in Xenopus laevis. For limbs at NF stages 45-53, we documented cell division patterns using BrdU labeling, and gene expression patterns for Sonic hedgehog which marks AP patterning, Sox9 which marks onset of cartilage formation, TH receptors TR&alpha and TR&beta which indicate tissue sensitivity to TH, and deiodinases which regulate cell levels of T4 and T3. TSH gene expression was used to gauge production of TH, which is undetectable at these stages. Cell division occurs uniformly across the limb bud until NF 50, after which it is excluded from central regions that start expressing Sox9. At no stage do BrdU labeling patterns suggest the presence of a progress zone, as hypothesized for amniotes. TR&alpha and TR&beta expressions are uniformly strong across the limb from its appearance to onset of differentiation, but become excluded from the shafts of differentiated cartilages. These results will provide the background for experimental analyses of the effects of TH exposure and deprivation on limb patterning and morphogenesis.
