Laboratory of Developmental Genetics, National Institute if Genetics, Mishima, Shizuoka 411, Japan
(Received May 30, 1989; Accepted July 3, 1989)
Keywords: Injury, Hydra, Head, Regeneration
Abstract. The effect of injury of hydra head regeneration was examined. Three different procedures, termed standard amputation, ligation, and mirror-image-grafting were used to remove the head from a polyp of the standard wild-type strain of Hydra magnipapillata (strain 105). A significantly reduced percentage of head regeneration was obtained by mirror-image-grafting at the mid-gastric region. Lateral transplantation was employed to examine the changes in head activation and inhibition levels after amputation. It was shown that the increase in head activation level after amputation was greater in normally amputated polyps than mirror-image-grafts, whereas the decrease in head inhibition level after amputation showed no apparent difference between the two procedures. These observations show that not only decapitation but also the state of the injured tissue after decapitation have a strong effect on the activation increase and subsequent head regeneration. This strongly supports the "injury effect". proposed by MACWILLIAMS (1982, 1983). An actual mechanism of the injury effect will be discussed.