Cell generation times in normal and talpid3 mutant chick limb mesenchyme

A comparative study of the cell cycle and its parameters, and of limb pattern development, was carried out in normal and talpid3 wing buds. The relative duration of the G2 + M phase is the least variable. The change in the length of the G1 phase and the S phase is associated with the appearance of mucopolysaccharides in chondrogenic zones and of myosin in myogenic zones. The effect of the ta3 gene is failure of chondrogenesis-induced lengthening of the G1 phase to appear in the chondrogenic condensation in the limb mesenchyme. The data also raise the question of the possible role of the apical ectodermal ridge in control of the cell division rate in the sub-ridge region.