Nuclear Differentiation in Paramecium caudatum: Analysis by the Monoclonal Antibody against a Macronuclear Antigen.

To know molecular mechanism controlling the differentiation of somatic nuclei (macronuclei) in Paramecium caudatum, I obtained the monoclonal antibody 36B against a macronuclear antigen. Immunocytochemical observations showed that the antigen 36B was dispersed in macronuclei. But in late stationary phase, large aggregation of the antigen was observed in some stocks, though this was not observed in another stock. In addition, the 36B-positive portion in macronuclei seemed to contain smaller amount of DNA than the remaining portion. These observations suggest that the antigen 36B exists in nucleoli in the macronucleus. In the late stage of conjugation, the antigen 36B was retained in the degenerating fragments derived from old macronuclei as long as the fragments persisted. In the beginning of the development of new macronuclei, the antigen 36B was not observed in four macronuclear anlagen, but after a while it appeared in all of them. This shows that the macronuclear anlagen newly get the antigen 36B during their development. Since the appearance of the antigen 36B coincides with the stage when macronuclei are known to be transcriptionally active, the antigen 36B may be involved in the expression of genes in macronuclei. This is consistent with the possibility that the antigen 36B may be a component of nucleoli.