What are the signaling centers controlling limb bud formation? Apical Ectodermal Ridge The Apical Ectodermal Ridge (AER) controls identity along the proximal/distal axis. The AER is a ridge of thickened ectoderm that forms along the entire edge of the limb bud at the dorsal/ventral boundary. This thickened ridge is analogous to ectodermal placodes in that [...]

What experiments demonstrate how the apical-basal axes are patterned in the neural tube? The Neural Tube Dorsal-Ventral Axes and the Role of Shh Starting at the ventral end, the following structures comprise the spinal cord: floor plate; cell bodies of somatic motor neurons; cell bodies of commisural neurons; roof plate. The floor plate guides axons [...]

Where is the intermediate mesoderm and how does it form? The Primary Organizer dorsalizes the mesoderm, resulting in dorsal mesoderm (gives rise to somites) and intermediate mesoderm (gives rise to kindey and gonad). Intermediate mesoderm is located between the paraxial mesoderm and the lateral plate. It develops paired epithelial thickenings. These paired epithelial thickenings are [...]

What controls A/P Patterning of endodermal organs? Hox genes are expressed collinearly along the antero-posterior axis in the endoderm and mesoderm. Distinct Hox expression domains oft coincide with distinct intestinal domains. This is reminiscent of Hox gene expression in morphologically distinct rhombomere and somite units. However, Hox deletions generally cause malformations (instead of homeotic transformations) [...]

What Are Ectodermal Placodes? What Sensory Organs Do They Form? A placode is a thickened region of the ectoderm, and are induced at the anterior end of the neural plate where BMP levels are intermediate (this same region gives rise to neural crest cells). Ectoderm is epithelial, while the mesoderm contains both mesenchymal and epithelial [...]

Neural crest cells Where do they arise? Neural crest cells form at the anterior end of the neural plate, at the border of the epidermis and neural plate. This is where BMP levels are intermediate. Sensory placodes arise from this region and are induced by the same signals. Neural crest cells migrate through the anterior [...]

Role of dorsal-ventral patterning system (DPP/Sog vs BMP/chordin) in neurulation In Drosophila, the dorsal-ventral patterning system causes a ventro-lateral portion of the blastoderm layer to become committed to a neurectodermal fate. The presumptive neurectodermal cells develop from nuclei that contain moderate levels of nuclear dorsal protein. Following cellularization of the blastoderm and the onset of [...]

How Does the Node Compare To the Spemann Organizer? What Is the Node? Hensen’s Node is present in birds and mammals. The Spemann Organizer is present in Xenopus. The Node establishes l What Different Types of Mesoderm Arise? Their Derivates? Inducing Signaling Molecules? For example, we learned that the mesoderm that comes to occupy the [...]

What are each germ layer’s derivatives? Which are dorsal and which are ventral derivates? Endoderm Epithelial lining of respiratory tract and GI tract. Mesoderm There are dorsal/ventral differences in what the mesoderm gives rise to. This is induced by differences in dorsal and ventral endoderm. Organizer cells self-diffrentiate into dorsal mesoderm (notochord), organizer cells dorsalize [...]