Potential >. Fate 2 cell stage each cell is totipotent (Nuclei are totipotent – Nuclear Transfer Experiments Pluripotent Cells are Determined Potential = Fate Determined Induction Competence

What is the Inducer? Are cells Determined? Is it reversible or irreversible? Are cells Competent? At all times?

Spemann and Mangold: The Organizer The Inducer of Neural Ectoderm is ______.

Is all Ectoderm competent at all times? Dorsal Lip transfer to Early Gastrula Dorsal Lip transfer to Late Gastrula

Is Determination Irreversible? Future Neural Ectoderm from Early Gastrula Future Neural Ectoderm from Late Gastrula

Mechanism of Organizer Action The search for the "organizer molecule" was one of the first worldwide biological research programs. Researchers from Germany, the United Kingdom, the United States, the Netherlands, Japan, Finland, Belgium, and China all sort this elusive entity. neural induction could occur through a 150 micron thick, 0.8 micron pore size filter, strongly suggesting that the inducer was diffusible. Problems: Other tissues could stimulate the development of Neural Ectoderm Freezing cells and adding Methylene blue stain causes induction Molecules found to have organizer function: Follistatin, Chordin, Noggin, Xenopus nodal-related-3, and Cerberus