Method of Introducing Tritiated Thymidine into the Tissues of Hydra

Cellular, Metabolic, and Developmental Dimensions of Whole-Body Regeneration in Hydra

Here we discuss the developmental and homeostatic conditions necessary for Hydra regeneration. Hydra is characterized by populations of adult stem cells paused in the G2 phase of the cell cycle, ready to respond to injury signals. The body column can be compared to a blastema-like structure, populated with multifunctional epithelial stem cells that show low sensitivity to proapoptotic signals, and high inducibility of autophagy that promotes resistance to stress and starvation. Intact Hydra polyps also exhibit a dynamic patterning along the oral-aboral axis under the control of homeostatic organizers whose activity results from regulatory loops between activators and inhibitors. As in bilaterians, injury triggers the immediate production of reactive oxygen species (ROS) signals that promote wound healing and contribute to the reactivation of developmental programs via cell death and the de novo formation of new organizing centers from somatic tissues. In aging Hydra, regeneration is rapidly lost as homeostatic conditions are no longer pro-regenerative.

Cell Proliferation in Hydra: An Autoradiographic Approach

Hydra cells take up substantial amounts of tritiated thymidine if the label is injected into an animal's gastric cavity shortly after feeding. Autoradiographic analysis shows that the isotope becomes incorporated into cell nuclei. The distribution of labeled nuclei probably represents the pattern of cell proliferation and is similar to the distribution of mitotic figures in histological preparations. The data show that cell proliferation is distributed along the body column and that there is no localized growth zone.

Archeology as Anthropology: A Case Study

Anthropological inferences, made possible by advances in techniques for collecting data in archeological field work and the processing of data with a computer, permit a comparison to be made between the modern western Pueblos and their prehistoric background. One point in the development of Pueblo social organization (approximately A.D. 1200) is examined and compared with the present.