【正文】 A/proteins) localized in the vegetal region Vg1 is a member of TGFbeta family of signaling proteins The cortical rotation upon sperm entry can both specify the dorsal side of the amphibian embryo, and induce formation of the Spemann anizer The cortical rotation relocates those maternal factors , such as Wnt11 and Dishevelled protein originally located at the vegetal pole to a site approximately opposite to the sperm entry. These factors called dorsalizing factors specify their new location as the future dorsal side of the embryo, thus conferring the dorsalventral axis Model of the mechanism by which the Disheveled protein stabilizes betacatenin in the dorsal portion of the amphibian egg The role of Wnt pathway proteins in dorsalventral axis specification (I) E: Blocking the endogenous GSK3 in the ventral cells of the early embryo leads to formation of a second set of body axis The role of Wnt pathway proteins in dorsalventral axis specification (II) Model of the induction of the Spemann anizer in the dorsal mesoderm Localization of stablized betacatenin in the dorsal side of the embryo Activation of Wnt signaling activates genes encoding proteins such as Siamois Siamois and TGFbeta signaling pathway function together to activate the goosecoid gene in the dorsal portion Goosecoid as a transcription factor activates genes whose proteins are responsible for induction of the Spemann anizer in the dorsal mesoderm ? How was the anizer specified and formed? What caused the dorsal blastopore lip to differ from any other region of the embryo? ? What factors were being secreted from the anizer to create the dorsoventral and anteroposterior axes? ? How did the patterning of the embryo along the body axes bee acpanied? Mechanisms underlying role of the Spemann anizer in development of the body plan The functions of the Spemann anizer (I) ? The ability to selfdifferentiate dorsal mesoderm into prechordal plate, chordamesoderm (notochord脊索 ) etc ? The ability to dorsalize the surrounding mesoderm into paraxial (somiteforming) mesoderm (When it would otherwise form ventral mesoderm) ? The ability to dorsalize the ectoderm, inducing the formation of the neural tube ? The ability to initiate the movements of gastrulation. Once the dorsal portion of the embryo is established, the movement of the involuting mesoderm establishes the AP axis. In Xenopus (and other vertebrates), the formation of the AP axis follows the formation of the DV axis The functions of the Spemann anizer (II) ? The Organizer functions in setting up the dorsalventral axis by secreting diffusible proteins (Noggin, chordin, and follistatin) that antagonize/block the BMP signal. These diffusible proteins generate a gradient of BMP signaling that specifies the DV axis ? The Organizer is able to secret the Wnt blockers Cerberus, Dickkopf and Frzb in the anterior portion of the embryo that generate a gradient of Wnt signaling. Thus, the Wnt signaling gradient specifies the AP axis. The diffusible signal proteins secreted by the Spemann anizer (I) The Organizer functions in setting up the dorsalventral axis by secreting diffusible proteins (Noggin, Chordin, and Follistatin) that antagonize/block the BMP signal. These diffusible proteins generate a gradient of BMP signaling that specifies the DV axis Localization of noggin mRNA in the anizer tissue At gastrulation, noggin is expressed in the dorsal blastopore lip During convergent extension, noggin is expressed in the dorsal mesoderm (the notochord, prechordal plate etc ) Noggin protein is important for development of the dorsal and anterior structures of the Xenopus embryo Rescue of dorsal structures by Noggin protein Most top: The embryo lacks dorsal structures due to exposure to