In turn, the activation of T-box protein activates signaling cascades that involve the Wnt signaling pathway and FGF signals. Before limb development begins, T-box proteins initiate FGF10 expression in the proliferating mesenchymal cells of the lateral plate mesoderm, which form the limb bud mesoderm. WNT2B and WNT8C stabilize this FGF10 expression in the forelimb and hindlimb, respectively. This FGF10 expression stimulates WNT3 expression in the above ectodermal cells – resulting in formation of the apical ectodermal ridge as well as inducing FGF8 expression. The FGF8 secreted by the AER acts to keep the cells of the limb mesenchyme in a mitotically active state and sustains their production of FGF10. positive feedback loop between the limb mesenchymal cells and the AER maintains the continued growth and development of the entire limb.