EVOLUTION OF VERTEBRATE LIMBS - ROBUST MORPHOLOGY AND FLEXIBLE DEVELOPMENT

New information about molecular mechanisms of development can be combi ned with existing knowledge about embryology, anatomy and paleontology to allow for an increased understanding of evolutionary biology. The tetrapod limb is appropriate for such an approach since much is known about both its structural variation and development. To this end we ar e investigating molecular regulatory mechanisms in urodele limb develo pment and regeneration, Urodeles have unique patterns of limb developm ent compared to other tetrapods, In addition they are able to regenera te their limbs as adults, thus providing the opportunity to conduct co mparative studies of the molecular mechanisms involved in development and regeneration in an identical genetic background. We have investiga ted the role of several homeobox-containing genes in the control of gr owth and pattern formation during limb development and regeneration, a nd have found that although there can be considerable variation in the ways in which expression of these genes is regulated in time and spac e, their expression patterns relative to morphological landmarks is co nserved, These results suggest that the function of these genes is a d eeply conserved feature of all tetrapods, and may be the molecular man ifestation of the homology between different limb types. These conserv ed similarities are overlaid with changes in the time at which genes a re expressed and the sequence in which structures differentiate, It is these latter features that are most likely responsible for the wide v ariety of morphologies observed among tetrapod limbs.