Positive evidence for defective germ nucleus generated by transplantation in Paramecium tetraurelia

Three cell lines initiated by transplantation of the micronucleus into amicronucleate recipient underwent abortive autogamy: the micronuclei disappeared in 95% of the autogamous cells and nonfunctional macronuclear anlagen were formed in a few; all postautogamous cells died except when regeneration of fragments of the prezygotic macronucleus occurred. The physical basis for the abnormality was investigated by two series of transplantation experiments: (1) The micronuclei from these cell lines were transplanted into normal amicronucleates. The resulting combination nevertheless uniformly exhibited the same kind of abortive autogamy. (2) Micronuclei from normal cells were transplanted into cells of the three abnormal cell lines; this yielded cell lines that were able to undergo normal autogamy. The two experiments thus demonstrated that the physical basis of the abortive autogamy in the three cell lines resided in defective micronuclei in these, and not in any other possible defect in other parts of the cells. Some considerations also indicated that the defects in such micronuclei only originated during or after transplantation into the amicronucleate recipients.