Phenotypic conversion of mating type specificity induced by transplantation of macronucleoplasm inParamecium caudatum

Summary According to the classical genetic analysis inParamecium caudatumby Tsukii & Hiwatashi (1983), the E mating type of each syngen is expressed when the cell bears alleles specific for syngen at theMtlocus. The O mating type is expressed when cells are homozygous for the null allele,mt, at theMtlocus. In suchmt/mtcells the O syngen specificity is determined by alleles at two other loci calledMAandMB. Inthe study reported here, macronucleoplasmic transplantation technique was used to test the above hypothesis. When macronucleoplasm of type E3(mating type E of syngen 3) was injected into a macronucleus of type O12(mating type O of syngen 12), some recipients changed to type E of the donor syngen but some others changed to type E of the recipient syngen. Thus, syngen specificity of donor macronucleoplasm controlling type E was converted into that of the recipients, even though the latter has no gene that controls type E. When this transformant expressing type E of the recipiexnt syngen was re-injected back into E of the other syngen, the expression of the converted mating type in some way continued in the recipient. This suggests that syngen specificity of geneMtof the donor was changed to that of the recipients by intersyngenic transplantation of macronucleoplasm. We also obtained results suggesting that the gene dosage ratio ofMttomtorMttoMAandMBmay be important for syngen specific expression of type E.