Effect Of The Apical Ectodermal Ridge On Mitotic Index In Hind Limb Bud Mesenchyme In Bufo Regularis

Abstract

The apical ectodermal ridge (AER) was formed at stage 51 of Bufo regularis, it persisted at stage 52 (limb bud acquiring paddle-shaped outline), then it disappeared by stage 53 (first indication of fourth and fifth toes). Mitotic index (MI) in the AER (stage 51) was higher (40%) than that of the apical ectoderm at stage 50, then it decreased (15%) by stage 52. By apical ectoderm removal at stage 50, the wound epithelium formed an AER by stage 51. The operated bud (80% of cases) showed a decrease in its volume and there was no significant difference in mesenchyme MI. By AER removal at stage 51, it reformed showing normal appearance (70% of cases), and a pronounced decrease in limb size was also observed. Mesenchyme MI (stage 51) was decreased 30% distally and 20% proximally, then distal mesenchyme revealed another decrease (15%), and by stage 52, MI increased distally (20%). Proximal mesenchyme exhibited a pronounced decrease (40%). It is suggested that AER removal reduced the mesenchyme mitotic activity and caused delaying of limb development in early stages, and might play an important role in morphogenetic pattern and in maintaining outgrowth.