He then partially constricted the egg, causing all the nuclear divisions to remain on one side of the constriction. His procedure was ingenious: Shortly after fertilizing a newt egg, Spemann used a baby's hair taken from his daughter to lasso the zygote in the plane of the first cleavage. The experiment that began this research program was performed in 1903, when Spemann demonstrated that early newt blastomeres have identical nuclei, each capable of producing an entire larva. More recently, the discoveries of the molecules associated with these inductive processes have provided some of the most exciting moments in contemporary science. The experiments of Spemann and his students framed the questions that experimental embryologists asked for most of the twentieth century, and they resulted in a Nobel Prize for Spemann in 1935. That such inductive interactions were responsible for amphibian axis determination was demonstrated by the laboratory of Hans Spemann at the University of Freiburg.
Such interactions are called inductions (see Chapter 6). In Chapter 3, we discussed the concept of regulative development, wherein (1) an isolated blastomere has a potency greater than its normal embryonic fate, and (2) a cell's fate is determined by interactions between neighboring cells. Amphibian axis formation is an example of regulative development. Rather, they arise progressively through a sequence of interactions between neighboring cells.
Vertebrate axes do not form from localized determinants in the various blastomeres, as in Drosophila. The Progressive Determination of the Amphibian Axes
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