Nucleo-Cytoplasmic Interaction During Macronuclear Differentiation in Ciliate Protists: Genetic Basis for Cytoplasmic Control of SerH Expression During Macronuclear Development in Tetrahymena thermophila

ABSTRACT A novel class of mutations affecting the developmental expression of SerH cell surface antigen genes of Tetrahymena thermophila is described. Unlike previous categories of mutation, the four independently isolated mutations of this class act through the cytoplasm to affect SerH genes during macronuclear development. That is, macronuclei which develop under the influence of mutant cytoplasm do not subsequently express H, most likely because the developmental processing of SerH genes is affected. The cytoplasmic effect is specific for the SerH locus and is independent of which SerH allele is present. In place of H, hitherto unknown antigens are expressed. Expression of SerH can be rescued during development either by wild-type cytoplasm exchanged between conjugants or by the homozygous wild-type genotype. The mutations segregate independently of the SerH genes and identify one, possibly two, bistable genes. Possible models to explain these results are discussed.

GENES INFLUENCING SELECTIVE FERTILIZATION IN NEUROSPORA CRASSA

ABSTRACT The mutual attraction of conidia to protoperithecia of the opposite mating type was studied genetically in crosses where a mixture of conidia from two different strains, one of which was marked by an ascospore color mutant gene tan spore (ts), was applied to protoperithecia. Selective fertilization was measured as the frequency of perithecia fertilized by conidia from one strain in competition with conidia from another strain. Selective fertilization by a given strain varied throughout the range from 10 to 97% according to the strains of protoperithecial parent. The selective fertilization was revealed to be under the control of two or more loci, which appeared to have multiplicative action. No indication of a cytoplasmic effect on selective fertilization was obtained. The strength of the mutual attraction between conidia and protoperithecia decreased as genetic similarity increased.