Novel tools for the study of development, migration and turnover of nematocytes (cnidarian stinging cells).

The rhodamine derivatives tetramethyl-rhodamine-5/6-maleimide (TROMI) and tetramethyl-rhodamine-6-isothiocyanate (TRITC) were allowed to react with living Hydra vulgaris. The two fluorescent dyes stain the polyps to different degrees, apparently without impairing their viability and behaviour. Concerning nematocytes, TROMI preferentially couples to cytoskeletal elements only of mounted nematocytes whereas TRITC selectively reacts with structural components of cysts of late nematoblasts, which thereafter develop apparently normally into mature nematocytes. Hence TROMI-labelling indicates that nematocytes are mounted and ready for discharge; TRITC-labelling can be used as a tool to investigate the final maturation, migration and installation of nematocytes in Hydra. Together with a new non-fixative method to dissociate Hydra polyps into single, identifiable cells, the two labelling methods allow direct quantitative dynamic studies of nematocyte turnover and open new possibilities of investigating the regulation and the mechanisms of nematocyte supply and migration.