Experimental studies on axial polarity in hydra

Abstract

There is evidence which suggests that the polarity of regeneration in hydra is determined by axial gradients of some sort. The mechanisms which may be involved in the establishment and maintenance of the gradients have been investigated by studying the reversal of polarity in graft combinations. Complete polarity reversal can be effected by a grafted hypostome or by a grafted hypostome and peduncle. Partial polarity reversal can be effected by a graft of a peduncle only. Changes in regional properties associated with polarity changes have been investigated using isolation and transplantation techniques. The experimental results suggest that the axial gradient behaves as a gradient of a substance. Such a gradient could be produced by either (a) simple diffusion of a substance from a source or (b) unidirectional transport of a substance plus back-diffusion. Some of the experimental results are incompatible with mechanism (a). All the experimental results are compatible with mechanism (b). Some of the problems raised by the interpretation of the axial gradient in terms of a polarized transport model are briefly discussed.

Canalized Morphogenesis Driven by Inherited Tissue Asymmetries in Hydra Regeneration

“…The polarity of regenerating Hydra tissues can also exhibit substantial plasticity and even be reversed under certain conditions, generated, e.g., by grafting different tissues or the application of exogenous Wnt [ 10 , 11 , 20 , 21 ]. Recent results highlight the importance of injury response in activating the Wnt signaling pathway associated with oral regeneration [ 16 , 17 , 18 , 22 ].…”

Signaling gradients in surface dynamics as basis for planarian regeneration

“…Hydra. The regeneration of hydra, a freshwater polyp, shows similarities to that of planarians, with comparable outcomes for most of the experiments mentioned above; see [80,33,71,70,12,84] and references therein. Different In grafting experiments (center), the head region of a donor planarian is grafted into a host planarian, retaining roughly the distribution of cell concentrations and signaling molecules from its original location.…”

Positional information and tissue scaling during development and regeneration

“…Adult Hydra polyps retain a permanent stem cell population, and axial polarity is maintained by signals from the hypostome (Hobmayer et al, 2000). If the head and foot parts of the animal are removed, the gastric section regenerates and maintains the original polarity (Wilby and Webster, 1970). After mid-gastric bisection, both pieces regenerate the missing body parts, with head-organizer activity being established after 3 h in the head-regenerating tip and retained for about 2 days (MacWilliams, 1983).…”