Chapter IX Regulation of Cell Divisions in the Sea Urchin Embry

Abstract

Publisher Summary This chapter explains the regulation of cell divisions in the sea urchin embryo. The results presents in the chapter are compatible with the interpretations that mitoses in the growing sea urchin embryo are coordinated by a wave-like propagation of a chemical signal travelling along the embryonic axis. It is postulated in the chapter that the periodic event has the characteristics of a limit cycle oscillator originating from the instability of a biochemical feedback loop. This hypothesis is consistent with the results obtained with Actinomycin D, showing that the cell-division process is not inhibited by the block of genetic expression, thus suggesting a “cytoplasmic” localization of the mitotic clock. However, Actinomycin D treatment results in a practically “chaotic” pattern of mitoses when administered prior to the segregation of the micromeres. An important role may also be played by the cell interactions; the propagation of the signal from cell to cell can occur with suitable junctional contacts.