Isolation of a marker for head-specific cell differentiation in hydra

A cDNA was isolated from Hydra vulgaris coding for a 360 amino acid long polypeptide with no significant similarity to any known protein. In situ hybridization showed that the corresponding transcript is expressed exclusively in endodermal cells of the hypostome, hence its name hyp 1. Hyp 1 therefore represents a highly specific marker for the head region of hydra. In accordance with this, we found that hyp 1 expression was strong in tissues regenerating a head. Hyp 1 reappeared early during head regeneration, namely 6–8 h after initiation of regeneration by cutting. These findings imply that hyp 1 is an excellent marker for monitoring early events in head-specific differentiation processes in hydra.