Studies on pattern regulation in Hydra. IV. The effect of colcemide and puromycin on polarity and regulation.

Regulation in hydra is polarized, the new hypostome always forming at the distal end of an isolated piece. Polarity is rigorously maintained in such pieces but can be altered in graft combination (Peebles, 1900; King, 1901; Morgan, 1901; Browne, 1909; Goetsch, 1929; Tardent, 1960; Webster, 19666). Previous investigations (Webster, 1966a, b; Webster & Wolpert, 1966) have suggested that polarized regulation occurs as a result of the interaction of three factors: time for hypostome determination, inhibition of hypostome determination and threshold for inhibition. All these factors appear to be graded along the axis. There is some evidence that time for hypostome determination and threshold for inhibition are closely linked factors (Webster, 19666) and in many experiments it is not possible to distinguish between them. For this reason they are referred to throughout this paper as 'time-threshold' factors or properties. If polarized regulation does result from interaction between the above factors, then experimental alteration of polarity would be expected to depend upon interference with these factors or with their interaction. Experimental alteration of polarity in graft combinations has previously been discussed in such terms (Webster, 19666) but no attention has been devoted to experimental alteration by other means. This is the subject of the present paper. A large body of literature exists on the effect of various environmental factors (chemical agents, temperature, electric current, etc.) on regulation and polarity (see e.g. Child, 1941). In some hydroids, but not hydra, polarity is normally rather labile and can be influenced by a variety of environmental factors. Tubularia is a good example (literature reviewed by Child, 1941; Tardent, 1960, 1963). Corymorpha is a hydroid which often shows bipolar regulation in short pieces and the frequency of such forms can be increased by exposing the pieces to inhibitory agents (cyanide, alcohol, low temperature, etc.)