Cyclic Changes in Shape of A Non-Nucleate Egg Fragment of Tubifex (Annelida, Oligochaeta)

A non-nucleate fragment separated from the fertilized Tubifex egg at metaphase of the second meiosis showed temporary surface deformation at 3–3.5 hr intervals, i.e. , synchronously with the onset of formation of the second polar body and early cleavages in control eggs. From the two-cell stage on, the periodicity of the surface activity in the non-nucleate fragment was found to be synchronous with the cleavage cycles of the CD-cell and its descendants, but not with those of the AB-cell. This surface deformation was completely inhibited by cytochalasin B (50 μg/ml). Electron microscopy shows that microfilaments are present exclusively in the cortical layer of the deforming fragments. Cycloheximide-treated egg fragments commenced surface deformation after a delay of 1–2 hrs; pulse-treatment indicated that the surface deformation requires proteins synthesized specifically during the period of the previous surface deformation. These results are discussed in relation to the nucleus-independent cytoplasmic rhythm and asynchronous cleavage of Tubifex eggs.