DNA Synthesis and Cell Movement during Regeneration inTubularia

After hydranth removal of Tubularia the level of DNA synthesis, measured by nuclear incorporation of thymidine-H3. is uniform throughout the caulus from the time of hydranth amputation through wound healing. Synthesis is then suspended during massive cell movements until the primordium begins to form; activity resumes in both the ectodermis and endodermis in all subsequent regenerative stages with qualitative and quantitative differences along the caulus. Incorporation is highest in the proximal ectodermis and grades off distally; in the endodermis uptake increases in a distal direction and becomes highest in the primordium. As differentiation continues, synthesis appears in the future gonophore region, the inter-tentacular zone, and the developing tentacles. When differentiation is completed, further uptake occurs in the peduncle, basal hypostome, and both cell layers of the tentacles. Monitoring the movement of hydrocaular cells, labeled at amputation, confirms that there is a general shift of the coenosarc along the entire length of the caulus toward the distal end. Cells continue to migrate from both cell layers of the caulus into the hydranth primordium even after it is formed. Labeled proximal cauli grafted to unlabeled distal halves indicate that cells from the ectodermis and endodermis still contribute to the hydranth regenerate. There is no evidence for reverse cell movement. Incorporation of thymidine-H3 (suspended during massive cell movements) does accompany individual cell migration.