CNIDOCIL REGENERATION IN NEMATOCYTES OF HYDRA

By means of light and electron microscopy we demonstrate that nematocytes of Hydra attenuata regenerate lost cnidocils within 3 h. Following decnidociliation by treatment with 6% ethylene glycol, cnidocil regeneration starts within 5 min. For about 2 h the elongation rate is nearly constant. Cnidocils can be regenerated over at least three successive decnidociliation and regeneration cycles. The regeneration is completely inhibited by micromolar concentrations of colchicine. However, inhibitors of protein synthesis, such as cycloheximide or puromycin, do not completely block regeneration but reduce its capacity to two cycles with diminished cnidociliar length. This indicates that nematocytes contain a pool of cnidociliar precursor proteins. During cnidocil elongation, an increased number of vesicles can be observed at the cnidocil base. About 20 min after decnidociliation the cnidocils come into contact with the surrounding stereovilli. The components become connected by intermembrane linkages which increase in number until the cnidocil grows out of the stereovillar cone. Thereafter, further elongation of the cnidocil occurs without changes in the linkages. The nematocytes lose mechanical and/or chemical sensitivity by decnidociliation but become excitable again before complete restoration of the original cnidociliar length. © 1990 Springer-Verlag.