Meiosis and Nuclear Behavior in Tetrahymena pyriformis*

Abstract

SUMMARY. Chromosome behavior of strains WH‐6, and WH‐14 mating types I and II respectively of variety 1, of T. pyriformis was studied during conjugation. Meiosis takes place during the first two prezygotic divisions. The chromosomes are at late pachytene‐early diplotene during the maximum elongation of the crescent in prophase of the first micronuclear division. As the crescent shortens, five bivalent chromosomes are readily recognized. Five dyads go to each pole at the end of the first division. Following a brief interphase the second meiotic division results in four micronuclear products, each with five chromosomes. Three of these products disintegrate; the fourth undergoes mitosis resulting in two pronuclei each with five chromosomes. Following a reciprocal interchange of the migratory pronuclei between the two conjugants, the synkaryon of each is formed just anterior to the macronucleus. The diploid number of ten chromosomes has been counted at the first division of the synkaryon.

Tetrahymena contain two distinct and unusual high mobility group (HMG)-like proteins.

“…To gain more insight into possible functions of these proteins, the synthesis of LG-1 and LG-2 during the sexual phase of the Tetrahymena life cycle, conjugation, was investigated. Conjugation is an ordered developmental process during which cells of opposite mating type pair, undergo meiosis, and genetic exchange that results in the formation of new somatic (macro-) and germinal (micro-) nuclei (Ray, 1956). To determine when during conjugation LG-1 and LG-2 are synthesized, mating cells were pulsed for 1 h with [3H]lysine at various times throughout conjugation.…”

Phosphorylation of the SQ H2A.X Motif Is Required for Proper Meiosis and Mitosis in Tetrahymena thermophila

“…During Tetrahymena conjugation, micronuclei undergo meiosis, adopting a highly elongate crescent shape (60). During crescent formation the round MIC elongates gradually to the crescent form, which, when maximally extended, can be up to twice as long as the cell, and then shortens and condenses at metaphase I.…”

CHROMOSOMAL ASSOCIATION AND ARRANGEMENT AT MEIOTIC PROPHASE OF THE MICRONUCLEUS IN <i>PARAMECIUM</i>

“…Moreover, end-to-end chromosomal association is known in Tetrahymena which has the most prominent crescent (Ray 1956;Sugai and Hiwatashi 1974). In this case, a chromosome of genome size was observed in the pachytene crescent, while five bivalents were found at meiotic metaphase I.…”