The vegetal cells produce ligands of the TGF-beta superfamily that have a role in inducing ventral mesodermal cell fates. The organizer is thought to function in large part by inhibiting certain TGF-beta signals. The cells of the organizer secrete molecules that bind and inactivate these TGF-beta ligands. Inhibitors of Wnt signals have also been shown to mediate organizer function. The inhibitors secreted by the organizer dorsalize surrounding tissues.
Dorsalized ectoderm adopts a neural cell fate.
Many other transcription factors and signaling molecules have been identified as having important roles in organizer function. They are described in your text. As endodermal and mesodermal cells are internalized during gastrulation, they appear to adopt appropriate anterior-posterior fates. As shown in Fig. 10.39, they can also induce the corresponding A-P identities in overlying ectoderm.