Developmental mechanism involved in the embryonic reduction of limbs in reptiles.

ABSTRACT

The purpose of the studies here reported was to explain the mechanisms responsible for the reduction of limbs in the serpentiform reptiles. Descriptive and experimental embryology, ultrastructural studies, chemical action (with Ara-C) on embryos and (3H) thymidine autoradiography of limb buds were used in this study; they provide evidence that defects in the morphogenetic mechanisms involved in the development of limbs (somitic deficiency, incomplete differentiation and premature degeneration of the apical ectodermal ridge) are responsible for the cessation of growth of the limb buds in these reptiles. At the biochemical level, a strong decline in the rate of DNA synthesis in the mesodermal cells of the limb bud (during and after the degeneration of the apical ridge) is the main causative factor of the evolutionary arrest of limb development in serpentiform reptiles.