Life stage specific expression of a myosin heavy chain in the hydrozoan Podocoryne carnea

In order to study life stage specific gene-expression and also to investigate the molecular components of jellyfish muscle we cloned a tissue specifically expressed cDNA of the metagenetic hydrozoan Podocoryne carnea. A monoclonal antibody was made that reacts with the filaments of striated muscle of the medusa stage. The mAb detects a protein of 220 kDa in Western blots. The antibody was used to clone a cDNA from an expression library. Sequence analysis showed that the clone codes for the rod part of a myosing heavy chain (MHC). Surprisingly, the sequence is more similar to MHCs from striated muscle than to smooth muscle or non-muscle MHCs from either invertebrates or vertebrates. A particularly well conserved region, which may be correlated to a function in striated muscle, was found. Expression studies showed that the corresponding RNA is only present in the striated muscle cells of the medusa. During medusa development, the transcript became detectable at the same time as muscle differentiation becomes visible in the electron microscops.