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

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Abstract
A non-nucleate fragment separated from the fertilized Tubifex egg at metaphase of the 2nd meiosis showed temporary surface deformation at 3-3.5 h intervals, i.e., synchronously with the onset of formation of the 2nd polar body and early cleavages in control eggs. From the 2-cell stage on, the periodicity of the surface activity in the non-nucleate fragment was 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 .mu.g/ml). EM 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 h; 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.