THE CAMP RESPONSE ELEMENT-BINDING PROTEIN IS INVOLVED IN HYDRA REGENERATION

Hydra provides an interesting developmental model system where pattern formation processes are easily accessible to experimentation during r egeneration. Previous studies have shown that the neuropeptide head ac tivator affects cellular growth and head-specific cellular differentia tion during head regeneration and budding. In order to investigate the signal transduction pathway and the regulatory genes involved in thes e processes, we measured cAMP levels after head activator treatment an d found that head activator leads to an increase in cAMP levels at con centrations where effects on nerve cell determination and differentiat ion are observed (10(-11) to 10(-9) M). Moreover, exposure of intact h ydra to a permeable form of cAMP stimulates nerve-cell differentiation and thus mimicks the effect of endogenous head activator. Band-shift assays were performed to detect changes in hydra nuclear protein bindi ng activity during regeneration or after head activator treatment. We found that the cAMP response element (CRE) promotes a specific and str ong DNA-binding activity which is dramatically enhanced and modified d uring early regeneration or after HA treatment. We also identified a s urprisingly highly conserved hydra gene encoding the cAMP Response Ele ment Binding protein, which is involved in this CRE-binding activity. Initiation of regeneration upon wounding provokes an endogenous releas e of HA which leads to the final differentiation of determined nerve c ells. We propose that the nerve-cell differentiation observed within t he first 4-8 hours of regeneration relies on the agonist effect of hea d activator on the cAMP pathway, which would in turn modulate the CRE- binding activity of the hydra CREB protein and thus regulate the trans criptional activity of genes involved in regeneration processes.