Monoclonal antibody against a conjugation-specific nuclear antigen in Paramecium caudatum

To understand molecular mechanisms controlling the sexual reproduction process (conjugation) in Paramecium caudatum, we have tried to detect conjugation-specific antigens with monoclonal antibodies. We obtained a monoclonal antibody (CSN-1) against an antigen that appears in the nuclei only during conjugation. This nuclear anti-gen began to appear both in micro- and macronuc-lei at micronuclear stage II or III early in the conjugation process (4 h after the mating reaction at 25°C). In the macronucleus, the nuclear antigen persisted until the stage of macronuclear fragmen-tation (about 35 h) and then disappeared before degeneration of the macronuclear fragments. In the micronucleus, the antigen existed until the crescent stage (stage V) of the first meiotic division (8h). The antigen in the micronucleus disappeared after the crescent stage but reappeared again in the eight nuclei produced by the third postzygotic division (25 h). Then it persisted only in the four macronu-clear anlagen differentiated from the eight nuclei (about 30 h). When exconjugant cells had under-gone two successive postconjugational cell div-isions and thus possessed only one new macronuc-leus as in the vegetative cells, the antigen disappeared completely from the new macronuc-leus in most cells. These cells without the antigen began to appear about 50 h after the mating reac-tion. As the antigen is specific to conjugation and localized in nuclei, it may play some important role(s) in the conjugation process