Hydra tropomyosin TROP1 is expressed in head-specific epithelial cells and is a major component of the cytoskeletal structure that anchors nematocytes

A cDNA clone encoding a 253 amino acid tropomyosin was isolated from Hydra in a differential screen for head-specific genes. The Hydra tropomyosin gene, designated trop1, is a single copy gene, lacks introns and is strongly expressed in tentacle-specific epithelial cells. Analysis of protein synthesis in head and gastric tissue indicated a high rate of tropomyosin synthesis in head tissue. Immunolocalization of tropomyosin in tentacle tissue revealed a cushion-like tropomyosin-containing structure within battery cells at the base of nematocytes. The structure appears to form part of the cytoskeletal anchor for nematocytes. Tropomyosin cushions were also observed in epithelial cells along the body column, which contain mounted stenotele nematocytes.