PATTERN REGULATION IN AUTOGRAFTS OFHYDRA OLIGACTIS: POSITIONAL VALUES AND DIFFUSABLE MORPHOGENS

Abstract

Grafted Hydra oligactis are employed in this study in an attempt to determine if head regeneration in autografts of the species conforms to a positional-information-type control. Two groups of hydras are used: one group has the gastric regions reversed (g-reversal), and a second group with gastric regions and budding regions reversed (gbr-reversal). Regeneration of secondary (2°) heads in the original subhypostomal region of the reversed body regions is observed for both groups at 48, 72, and 96 hours post-grafting. Secondary heads occur in both groups with a significantly greater frequency of 2° heads forming in the gbr-reversal group. These results concur with those seen in "multiply-grafted" hydras wherein tandemly arranged gastric regions are inserted into the grafted animal. Namely, 2° head formation is more frequent at borders located progressively farther from the terminal head. The findings of this study argue strongly for the occurrence of an inhibitory signal (positional information signal) being superimposed upon the graded positional values (for head formation) along the hydra's body column. Furthermore, this study demonstrates that the occurrence of similar results in "multiply-grafted" hydras is a function of intrinsic controls of pattern formation and not an artifactual consequence of abnormal elongation of the animals.