Specific DNA rearrangements in synchronously developing nuclei of Tetrahymena.

Abstract

Specific rearrangement of internal chromosomal regions occurs during development of the somatic macronucleus in Tetrahymena thermophila and results in elimination of germ-line (micronuclear) DNA sequences. The timing and mechanism of genome rearrangement within one particular 9.3-kilobase region, which contains three distinct eliminated sequences, were investigated. Portions of this cloned region were used as probes in Southern hybridization experiments to analyze DNA from developing macronuclei (anlagen). All three deletions were found to occur predominantly within a 2-hr time period in which the nuclear DNA contents increased from 4C to 8C (1C represents the amount of DNA present in a haploid genome). The three deletion events can occur independently because intermediate forms, having sustained one or two deletions, were detected. One of the deletions occurs in two alternative ways, resulting in two equally abundant products of different size. Because reciprocal products expected from unequal sister chromatid exchange were not detected, an intramolecular DNA splicing mechanism is suggested.

Centromeric Histone H3 Is Essential for Vegetative Cell Division and for DNA Elimination during Conjugation in Tetrahymena thermophila

“…However, an alternative possibility is that lack of zygotic expression of Cna1p may induce a checkpoint response that blocks NM development. Consistent with this idea is the observation that the second endoreplication of the NM genome, which occurs about the same time as DNA elimination in wild-type cells (3), is inhibited during conjugation of ⌬gCNA1 cells (Fig. 6C and 7B and C).…”

“…The first endoreplication occurs after the second postzygotic mitosis as the new MACs swell. The second occurs in exconjugants when the DNA elimination structures are formed (3). Because the size of the NMs changes little after the initial swelling, the second endoreplication was visually detectable when wild-type cells were stained with DAPI (Fig.…”

A family of DNA sequences is reproducibly rearranged in the somatic nucleus ofTetrahymena

“…That Is, a mic sequence may be rearranged In more than one way. Such variability has been reported In studies of rearranged sequences In caryonides (the four cells from a mating pair) (12,13).…”

Extreme heterogeneous composition of the Paramecium caudatum macronuclear genomic DNA between hemoglobin and nucleosome assembly protein-1 genes

“…This result raised several possibilities: (1) a hb gene family exists whose members are structurally and functionally related (Usuki et al, 1989), and are distributed on distinct chromosomes, like the mammalian α and β hb genes (Hardison, 1998); (2) several copies of the same or highly related hb gene, produced recently by gene duplication generating a tandem repeated gene cluster similar to mammalian and invertebrate hb gene clusters (Efstratiadis et al, 1980;Antoine and Niessing, 1984), exist; (3) IESs at the hb gene or its flanking regions are excised alternatively or differentially to generate heterogeneity during macronuclear development (Austerberry et al, 1984;Herrick et al, 1987); (4) IIDSs are imprecisely excised, leading either to chromosome fragmentation followed by the addition of new telomeres or to the rejoining of flanking sequences (Caron, 1992;Le Mouël et al, 2003); (5) homologous or non-homologous recombinations occur among the hundreds of copies of macronuclear DNA during or after macronuclear development (Deak and Doerder, 1998).…”