MUTANTS OF SEXUAL MATURITY IN PARAMECIUM CAUDATUM SELECTED BY ERYTHROMYCIN RESISTANCE

Abstract

Cells of Paramecium caudatum, syngen 3 usually become sexually mature about 50 fissions after conjugation. In order to study the genetic mechanisms that control fission-dependent expression of maturity, an attempt was made to obtain early mature mutants by treatment with N-methyl-N′-nitro-N-nitro-soguanidine. A new cytoplasmic marker, erythromycin resistance, was used to eliminate nonconjugant and macronuclear regeneration clones. Twenty early mature clones were obtained from five different mutagenized cultures. Three of them were genetically analyzed by crosses to wild-type stocks. The results show all three mutants to be controlled by incompletely dominant genes, i.e., the homozygotes became mature 20-25 fissions and the heterozygotes 15 fissions earlier than the wild-type clones. At least two different loci are suggested for the early maturity.

Factors Controlling the Length of Autogamy-Immaturity in Paramecium tetraurelia

“…Studies on sexual immaturity in P. multimicronucleatum, P. caudatum and P. bursaria, in which autogamy does not occur and thus there is no autogamy-immaturity, have shown that 1) its length is measured by some mechanism associated with the number of fissions (Kroll and Barnett, 1968;Miwa and Hiwatashi, 1970;Takagi, 1970), 2) its length is shortened by mytomicin (Miwa and Hiwatashi, 1970) or UV (Takagi, 1974) or codominant gene mutation (Myohara and Hiwatashi, 1978), 3) its length correlates with the length of the clonal life span (Smith- Sonneborn, 1981), 4) the transition from immaturity to maturity is stepwise and genetically controlled (Siegel, 1967;Takagi, 1988), and 5) immaturin, a protein of molecular weight 10,000 daltons, is responsible for maintaining the immature state (Haga and Hiwatashi, 1981;Miwa, 1984).…”

Artificial induction of autogamy inParamecium caudatum

“…Yt3 is a natural stock collected by Yuuji Tsukii. 27aG3 is an exautogamous clone derived from the early mature mutant clone Em IV-3S 27a established by Myohara & Hiwatashi (1978). Stock 16B205 is a CNR (non-reversal mutant) heterozygote produced by two back-crosses of 16B101 (cnrB/cnrB, Takahashi, 1979) to 27aG3.…”

Immaturin-Nuclease as a Model System for a Gene-Programmed Sexual Development and Rejuvenescence in Paramecium Life History

“…In most species of ciliates, the length of the immaturity period is determined by the number of cell divisions after conjugation, and this number differs among species [ 3 , 4 , 5 , 6 ]. An analysis of a few mutants that have altered the length of immaturity provides compelling evidence that genetic factors influence the duration of the immature phase [ 7 , 8 , 9 ]. Sonneborn proposed the importance of immaturity based on population genetics; the presence of sexual immaturity provides time for offspring from the same mating to scatter around each other, preventing mating between closest relatives and avoiding inbreeding [ 3 ].…”