Mutants of TETRAHYMENA THERMOPHILA with Temperature-Sensitive Food Vacuole Formation. I. Isolation and Genetic Characterization

Efficient mass transformation of Tetrahymena thermophila by electroporation of conjugants

Conjugating cells of the ciliate Tetrahymena thermophila were electroporated in the presence of plasmid DNA containing a paromomycin-resistant ribosomal RNA gene (rDNA). Cells were selected with paromomycin following 12-24 hr of growth on nonselective medium. Resistant cells appeared after 2-3 days. Processing vectors containing the micronuclear rDNA and somatic vectors containing the macronuclear gene transformed the cells, with the former yielding frequencies up to 900 transformants per microgram of plasmid DNA. A ribosomal protein gene (rpL29) conferring cycloheximide resistance also transformed conjugating cells. The transformation efficiency of the plasmid containing only the rpL29 gene was increased by insertion of an rDNA replication origin and by cotransformation and preselection with an rDNA vector. These results indicate that electroporation can be used for the production of large numbers of transformed Tetrahymena.

Polypeptides during early conjugation in Tetrahymena thermophila

As Tetrahymena thermophila cells differentiate from their vegetative life cycle to sexual reproduction, their polypeptide pattern undergoes a series of changes. These changes have been traced in extracellular, cellular, and subcellular compartments. The first alteration is induced by the nutritional shift-down and results in stimulation of at least one ciliary polypeptide and affects a series of polypeptides from other compartments. The second alteration is induced by mixing starved cells of complementary mating types and this stimulates the synthesis of nine ciliary polypeptides before pairs have formed and eight afterwards. At least five of these early and one of the late conjugation-related ciliary polypeptides are removed by low concentrations of EDTA, indicating that they are located on the external side of the plasma membrane. No differences were observed between polypeptides excreted during starvation and after mixing of complementary mating types. At Tris concentrations restrictive for conjugation, cilia lack the conjugation-related polypeptides. Some of these are instead found among the excreted polypeptides. Using O'Farrell gels and silver staining on isogenic cells of all possible mating types, we have been unable to correlate changes in polypeptide patterns to specific mating types.

Stage-specific changes in protein synthesis during conjugation in Tetrahymena thermophila

Conjugation in the free-living ciliate Tetrahymena thermophila is an inducible developmental system which results in a synchronized reorganization of the genetic material in both mates of a pair. The cytological events were followed by Feulgen stainings of simultaneously mating cells and protein synthesis was revealed using [35S]methionine pulse labelling and two-dimensional gel electrophoresis. At least 33 proteins, including 24 conjugation-specific proteins, with apparent molecular weights (Mr) between 61 and 200 X 10(3) are stimulated during conjugation. Two slightly acidic proteins (Mr 89 and 73 X 10(3), respectively) are stimulated shortly after mixing of mating-competent cells and mainly before tight pairs are formed. Ten proteins are stimulated during meiosis, and two of these (Mr 90 and 78 X 10(3), respectively) are particularly interesting, since they are highly stimulated and more basic (pI values around 8.5) than most other proteins detected. Twelve proteins are stimulated essentially between pairing and early macronuclear development, three are stimulated from shortly before zygote formation and during the post-zygotic divisions, and six are stimulated during late conjugation, at various parts of macronuclear development. The functions of the conjugation-stimulated proteins are discussed.

Osmotic shock prevents nuclear exchange and produces whole-genome homozygotes in conjugating Tetrahymena

Exposure of conjugating Tetrahymena to a hyperosmotic shock blocks the exchange of gametic nuclei and produces self-fertilized exconjugants that are homozygous for their whole genome. Cells are sensitive to this induction during a brief period after meiosis. The high efficiency of the treatment and the fertility of the progeny make this a useful method for the isolation of induced recessive mutations and enhances the value of Tetrahymena as an animal-cell model system in which genetic dissection is practical. The sharp peak of sensitivity is useful in the study of those cellular mechanisms responsible for the independent handling of several functionally distinct nuclei during conjugation.