Sequential Nuclear Differentiation in Tetrahymena

Abstract

UCLEAR differentiation is often responsible for phenotypic differences among genically identical lines in ciliates and is demonstrated by patterns of assortment in vegetative pedigrees. The first example of such a nuclear differentiation ( SONNEBORN 1937( SONNEBORN , 1939 was the "caryonidal inheritance" of mating types in syngen 1 of Paramecium aurelia. In this case, macronuclei usually differentiate in an "all-or-none" fashion early in their development, and mating types are distributed at the cell divisions at which whole new macronuclei are assorted. Macronuclear differentiation is also the basis for mating type determination in the Group B syngens of P. aurelia, which appeared initially to manifest "cytoplasmic inheritance" (SONNEBORN 1954; NANNEY 1957). In syngen 1 of Tetrahymena pyriformis, macronuclear differentiation is again responsible for intraclonal mating type differences, but the diploid subunits of a single compound macronucleus often differentiate to express different mating types and then continue to assort for many cell divisions (NANNEY 1956; ALLEN and NANNEY 1958). Submacronuclear differentiation and vegetative assortment have also been demonstrated to underlie intraclonal variations in the H-immobilization antigens (NANNEY and DUBERT 1960) and the esterase and acid phosphatase isozymes (ALLEN 1960(ALLEN ,1961 ALLEN, MISCH and MORRISON 1963).

GENETICS OF THE ST SEROTYPE SYSTEM IN TETRAHYMENA PYRIFORMIS, SYNGEN 1

“…Later work (BLEYMAN, SIMON and BROSI 1966), however, suggests that all H differentiation may occur before the first fission. Similar analyses for the mating-type locus indicate that differentiation occurs prior to the first macronuclear division (BLEYMAN, SIMON and BROSI 1966). The T serotype locus, however, does not differentiate until approximately 30 fissions (PHILLIPS 1967b), and the esterase and phosphotase loci do not differentiate until 40-50 fissions after conjugation (ALLEN 1965).…”

T Serotype Differentiation in Tetrahymena

“…Quantitative information on the Tbc heterozygote was first obtained from a vegetative pedigree experiment in which sublines from a Tbc (TBIC, P I E ) heterozygote were tested for H and T serotypes 65 fissions after conjugation (BLEYMAN, SIMON and BROSI 1966). At this time about 20% of the sublines were pure for either Tb or Tc, but 95% of the sublines were pure for H serotype.…”

“…The P-l locus has a third stable type found in low frequency which requires the presence of both parental alleles (ALLEN, MISCH and MORRISON 1963). The time of the phenotypic differentiations has been established for the H serotype system, as occurring in different cases before the first, second or third macronuclear division after conjugation ( NANNEY, NAGEL and TOUCHBERRY 1964; BLEYMAN, SIMON and BROSI 1966). Estimates for the other systems give 25 or more fissions after conjugation for the T locus, and at least 40 to 50 fissions for the E-1, E-2 and P-l loci (ALLEN 1965 and unpublished).…”

“…1963). In addition, cells heterozygous at three different loci with output ratios close to equality (Hcd, Tbc, E-lbc) begin segregating pure lines at three distinct times in the life cycle (BLEYMAN, SIMON and BROSI 1966;ALLEN 1965). Such precise sequential timing is not compatible with random loss of chromosomes or haploid sets or with random somatic crossing over.…”