Temporal Patterns in the Ciliated Protozoa

Bleyman, Lea K.

doi:10.1016/b978-0-12-156960-0.50009-x

Cited by 32 publications

(20 citation statements)

References 46 publications

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“…Some pairs halt conjugation before the development of a new macronucleus, retaining the parental macronucleus and, therefore, the parental phenotype. Since cells which have produced a new macronucleus in conjugation will not mate for 40 to 80 fissions (19), immaturity can be used as an assay to identify sexual progeny. In this cross, 116 pairs were isolated.…”

Section: Resultsmentioning

confidence: 99%

Isolation of homozygous mutants after induced self-fertilization in Tetrahymena.

Bruns¹,

Brussard²,

Kavka³

1976

Proc. Natl. Acad. Sci. U.S.A.

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(see ref. 5 for a review). The micronucleus, a diploid nucleus with about the same genome as the macronucleus (6), is capable of mitotic and meiotic division, is generally inert in transcription, but is active in conjugation; new macronuclei are developed following meiosis and subsequent exchange and fertilization of the micronuclei of a mating pair.The ability to isolate induced mutations is an obvious necessity in any modem experimental genetic system. Unfortunately, in Tetrahymena the ability to generate cells suitable for mutant selection is complicated by the separation of somatic and germinal functions into different nuclei. To be expressed, a mutation must reside in the macronucleus; to be heritable through conjugation, it must be in the micronucleus. Since progeny macronuclei are developmental derivatives of micronuclei following conjugation, schemes for mutagenesis must insert a mating between induction of mutations and selection for mutant phenotypes. In order to generate homozygotes for the expression of recessive mutations, the mating should be some form of self mating.The phenomenon of genomic exclusion has held great promise for mutagenesis since Allen (7,8) demonstrated that the first round of mating results in an induced self-fertilization; Fig. 1 outlines the events associated with the entire process. The sequence is initiated by mating with a strain containing a defective micronucleus; C*, a vegetative derivative of inbred strain C (7) is the best known of these, but other strains can induce the phenomenon. Although round one mating produces cells with homozygous micronuclei derived from the non-C* conjugant, the developmental process seemingly aborts before the production of a new macronucleus; newly formed macronuclei only occur as a consequence of a second round of mating. In order to recover homozygotes in mutagenesis, round one pairs must be isolated, cloned, and mated, to insure a remating of the same conjugants in round two (10).A related paper (9) 25 ,g/ml of cycloheximide (cy) and 15 ,ug/ml of 6-methylpurine (6-mp), respectively (17).As previously described (9), functional heterokaryons for each of the two dominant markers were created by constructing the resistant heterozygotes, subcloning after vegetative growth, and retaining subclones that expressed sensitivity. Homozygous heterokaryons were created by passing heterozygous functional heterokaryons through the first round of mating in genomic exclusion, and identifying by a suitable testcross the clones which had become homozygous for the desired alleles in the 3243

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Section: Resultsmentioning

confidence: 99%

Isolation of homozygous mutants after induced self-fertilization in Tetrahymena.

Bruns¹,

Brussard²,

Kavka³

1976

Proc. Natl. Acad. Sci. U.S.A.

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“…Though some possible explanations are discussed by Bleyman (1971), this problem requires a further study.…”

Section: Discussionmentioning

confidence: 96%

“…In the life cycle of Paramecium, the time of the onset of maturity is measured in terms of the number of fissions because notwithstanding the change of the length of immaturity under different environmental conditions, the onset of maturity depends upon the number of fissions after conjugation (Sonneborn 1957;Bleyman 1971;Miwa and Hiwatashi 1970). Though no extensive study on the onset of mating type instability under different environmental conditions has been performed so far, the conditions which cause fission rate to decline retarded the onset of mating type instability in actual time.…”

Section: Discussionmentioning

confidence: 99%

TEMPORAL PATTERNS IN THE APPEARANCE OF MATING TYPE INSTABILITY IN <i>PARAMECIUM CAUDATUM</i>

Myohara

Hiwatashi

1975

The Japanese journal of genetics

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“…The length of the immaturity interval is considered the most significant single character, for it estimates the time available for (dispersal between successive fertilizations [6]. While different species have different mean immaturity intervals, within species genetic variation is characteristic of every well-studied ciliate [6,14,[16][17][18], and some species even have a polymorphism in qualitative features such as the ability to undergo autogamy [ 19, 201. Our results in both the uniform environment (Table 2B) and the multiple environments (Table 3 B(1)) demonstrate that there is statistically significant genetic variation in the length of the immaturity interval in T. hegewischi. In both environments we estimated that a standard deviation of about 9 fissions was attributable to genetic factors.…”

Section: Genetic and Environmental Effects On The Immaturity Intervalmentioning

confidence: 99%

The immaturity interval in Tetrahymena: Genetic and environmental sources of variation

Nyberg¹,

Bishop²

1981

Dev. Genet.

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The development of sexual maturity has been studied in Tetrahymena hegewischi. Progeny lines d o not typically change from immaturity to mating with all different mating types during a single test interval, but about 30% d o mature abruptly. Some testers are more likely than others to participate in the earliest mating reactions of progeny lines which d o not mature abruptly. Subcaryonidal vegetative pedigrees of 10 pairs from 4 crosses revealed considerable intrapair variation in the time, measured in fissions, of maturity. The average intrapair coefficient of variation was 20%. A nested ANOVA revealed significant genomic effects on the immaturity interval, but no significant cytoplasmic or caryonidal effects; 56% of the total variation was non-genomic. Growth in different environments had highly significant effects on the immaturity interval. Subclones grown at 27°C with alternate day transfers took on the average 2 to 3 times as many fissions to mature as sister subclones grown at 27°C with daily transfers. Subclones grown at 18°C or 34°C and transferred on alternate days had intermediate maturation times. The greatest range in the immaturity interval among lines of the same genotype was from 34 to 143 fissions. The development of maturity in this species involves genetic control of timing, but the genetic differences are obscured by a large amount of intraclonal variation and sensitivity to the environment.

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Temporal Patterns in the Ciliated Protozoa

Cited by 32 publications

References 46 publications

Isolation of homozygous mutants after induced self-fertilization in Tetrahymena.

Isolation of homozygous mutants after induced self-fertilization in Tetrahymena.

TEMPORAL PATTERNS IN THE APPEARANCE OF MATING TYPE INSTABILITY IN <i>PARAMECIUM CAUDATUM</i>

The immaturity interval in Tetrahymena: Genetic and environmental sources of variation

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