Molecular Model for Limb Development

The paper proposes a possible molecular mechanism of cell fate specification during limb development. The mechanism is based on a step-by-step activation of cell determinants, which occurs at the transcriptional level. Activation of the next determinant (or reactivation of the previous one) occurs only after the next cell division, only one determinant being activated (reactivated) in each cell cycle. This mechanism may be a basis for both proximodistal and anteroposterior specification of cell fates. As a result of this mechanism, the limb bud mesoderm proves to be divided into cell areas. Cells of the specific area would be condensed to form the specific cartilaginous element.