29. Driesch performed famous ‘pressure plate” experiments involving intricate recombination with 8- celled Sea urchin embryo. This procedure reshuffled the nuclei that normally would have been in the region destined to form endoderm into the presumptive ectoderm region. If segregation of nuclear determinants had occurred, resulting embryo should have been disordered. However, Driesch obtained normal larvae form these embryos possible interpretations regarding the 8-celled sea urchin embryo are:
A. The prospective potency of an isolated blastomere is greater than its actual prospective fate
B. The prospective potency and prospective fate of blastomere were identical
C. Sea-urchin embryo is a “harmoniously equipotential system” because all of its potentially independent parts interacted together to form single embryo.
D. Regulative development occurs where location of a cell in the embryo determines its fate.
Which of the interpretation(s) is/are true?
(1) only A                                                      (2) only D
(3) only A and B                                             (4) A, C and D

The correct interpretations of Driesch’s famous “pressure plate” experiment with an 8-celled sea urchin embryo are:

• A. The prospective potency of an isolated blastomere is greater than its actual prospective fate.

• C. Sea-urchin embryo is a “harmoniously equipotential system” because all of its potentially independent parts interacted together to form single embryo.

• D. Regulative development occurs where location of a cell in the embryo determines its fate.

Statement B (that prospective potency and prospective fate were identical) is incorrect in light of Driesch’s findings because the experiment showed that the blastomere potency is greater than its usual fate.

Final Answer:

(4) A, C and D

Introduction

The debate over whether embryonic development is predetermined (“mosaic”) or involves cellular interactions (“regulative”) was significantly informed by Hans Driesch’s classic pressure plate experiments in sea urchins. By mechanically rearranging nuclei and blastomeres in 8-cell embryos, Driesch demonstrated the remarkable plasticity and regulative nature of early development.

Overview of Driesch’s Experiment

• Driesch compressed sea urchin embryos between glass plates at the 8-cell stage, mixing nuclei usually destined for specific embryonic regions.

• Contrary to expectations that such rearrangement would produce abnormal embryos, normal larvae developed.

• This suggested cells retained higher developmental potency than their normal fate and that embryonic cells function together as a harmonious system.

Key Conclusions from the Experiment

• The prospective potency (what a cell can potentially become) is greater than its actual developmental fate, meaning cells can compensate if moved or altered.

• Embryos are equipotential systems, where cells interact collectively to form a complete organism.

• Cell fate is influenced by cell position and the surrounding environment, highlighting the importance of regulative development.

Implications for Developmental Biology

• Driesch’s findings countered the mosaic theory, which postulated rigid, autonomous cell fates determined strictly by inherited factors.

• It laid the foundation for understanding how embryonic cells communicate and regulate each other to ensure proper development.

• These insights are fundamental to stem cell biology, regenerative medicine, and developmental genetics.

Conclusion

Driesch’s pressure plate experiment beautifully illustrated that early sea urchin embryos possess considerable regulative capacity. The differences between prospective potency and fate, the embryo’s equipotentiality, and the role of cell position collectively underscore a sophisticated system of developmental regulation beyond strict preformation.

Final Answer:
(4) A, C and D