A model for pattern formation of hypostome, tentacles, and foot in hydra: how to form structures close to each other, how to form them at a distance.
نویسنده
چکیده
A model for head, tentacle, and foot formation in Hydra is proposed. The model shows that systems which suggest a positional information scheme may be realized by a set of hierarchically coupled pattern forming systems: a structure generates the precondition for a second structure but excludes this structure locally. In this way, a well-regulated neighborhood of structures is enforced. According to the model, head, tentacle, and foot formation are under the control of separate activator-inhibitor systems. These systems are coupled via the source density. The head activator increases the source density and the activation takes place preferentially in regions of highest source density. The foot activation has the opposite behavior. It appears at the lowest source density and lowers the effective source density further. Therefore, head and foot activation appear preferentially at opposite positions of the field. Tentacle activation occurs in the region of highest source density that is not occupied by a primary head activation. Tentacle activation requires a certain threshold level of the source density. As shown by computer simulations, the model accounts for many so far unexplained observations, such as during regeneration the tissue obtains tentacle-like properties until the newly formed hypostome displaces the tentacles into a subhypostomal region. Since no direct inhibition between head and foot is involved, both structures can appear close to each other in experimental situations. The dramatic effects of treatment with diacylglycerol, such as the formation of new tentacles preceding the formation of additional hypostomes, become understandable under the simple assumption that the agent increases the source density. Budding is regarded as a trigger of a second head activator maximum. Budding can occur only beyond a minimum distance from the head due to the head inhibitor and beyond a minimum distance from the foot since the source density would be too low there. The model accounts for the periodic spacing of secondary structures around a primary organizing region such as that found in the arrangement of leaves and flower elements in plants around the primary meristem. Similarities to the vulva development of Caenorhabditis elegans and to the segmentation of insects are discussed.
منابع مشابه
Induction of secondary axis in hydra revisited: New insights into pattern formation
In 1909, several years before the famous `Organizer’ experiments of Spemann and Mangold, Ethel Browne demonstrated induction of a secondary axis in hydra by grafting a hypostome. Based on this and subsequent work, in the late sixties, Lewis Wolpert proposed the theory of morphogen gradients and positional information. We have studied secondary axis induction by hypostome and foot tissue using t...
متن کاملLinkage of several pattern forming reactions to generate complex structures: head, foot and tentacle formation of the freshwater polyp Hydra as an example
The complexity of patterns in higher organisms requires a hierarchical linkage of many pattern-forming reactions. Basic arrangements are two structures that appear either adjacent to each other or at opposite poles of a field. The freshwater polyp Hydra will be used to illustrate corresponding mechanisms. The hypostome (mouth opening) with the surrounding tentacles is an example for two adjacen...
متن کاملRedesigning Bazaar Physical Structure According to its Dealing Culture Structure- Case Study: Arab Bazaar in Ahvaz City
Redesigning Bazaar Physical Structure According to its Dealing Culture Structure Case Study: Arab Bazaar in Ahvaz City The Bazaar physical structure is formed from the arrangement syntax of division units, Interfaces, joints and boundaries to each other and the Arabic Bazaar also follows this example. This structure is the result of arrangement syntax of division units with linear pattern a...
متن کاملNucleic acid and protein synthesis and pattern regulation in hydra. I. Regional patterns of synthesis and changes in synthesis during hypostome formation.
Hydra provides a convenient system for the study of the regulation of a linear pattern of organization. Almost any region is capable of being reconstituted into the whole organism and regulation is always polarized, i.e. distal structures (hypostome and tentacles) are formed from distal ends and proximal structures (peduncle and basal disk) from proximal ends. Two models have recently been prop...
متن کاملInduction of secondary axis in hydra revisited: New insights into pattern formation
In 1909, several years before the famous `Organizer' experiments of Spemann and Mangold, Ethel Browne demonstrated induction of a secondary axis in hydra by grafting a hypostome. Based on this and subsequent work, in the late sixties, Lewis Wolpert proposed the theory of morphogen gradients and positional information. We have studied secondary axis induction by hypostome and foot tissue using t...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Developmental biology
دوره 157 2 شماره
صفحات -
تاریخ انتشار 1993