A CENTENNIAL DEBT OF DEVELOPMENTAL BIOLOGY TO THE SEA URCHIN

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Abstract
The fortunes of a field in Biology depend to a large extent on the organism selected for investigation. A successful case in point is the sea urchin in the study of development. The other side of the coin is that once such an organism has been discovered there is a tendency to consider it a general model for all organisms. Again, this has been the case of the sea urchin embryo. There is no question that the sea urchin embryo has played a key role in the field of embryology, equaled only by the amphibian embryo. Hence it seemed to me worthwhile to take the opportunity of this occasion to trace the early history of why and how the sea urchin came to acquire such a position. And in particular to analyze to what extent work on the sea urchin has contributed to laying the foundations of Cell and Developmental Biology, not only through important discoveries but also through the formulation of problems that have become central to present day Developmental Biology. Accordingly I shall confine myself to to the period that spans from the 1870s to the first decade of our century. Even granted this limitation the topic is too vast for this presentation, and hence I shall discuss only the three topics in which experiments with the sea urchin egg and embryo have either played a major role or have contributed significantly to the understanding of basic events of development. The three topics are: first, fertilization and initiation of development; second, the debate on the impact of evolution on the events of development; and finally, nuclear control of the events of development. When and why did the sea urchin start attracting the attention of zoologists interested in development? The earliest work on sea urchin development that I have been able to trace is that of Dufosse (1847). Even though his illustrations were rather crude, they nevertheless showed how well suited this embryo was for the study of development, its main advantages being its transparency and the ease with which it could be raised in the laboratory. Indeed, what zoologists were primarily aiming at, now that good quality microscopes were available, was to "see" what takes place within an egg while it develops; in this respect the sea urchin embryo was almost unique.

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