Modification of the DNA content in translocated regions of Drosophila polytene chromosomes

Abstract

The DNA content of translocated polytene chromosome regions in Drosophila melanogaster is affected by heterochromatic position effect. Microdensitometric studies on wm258-21 translocation heterozygotes showd (Hartmann-Goldstein and Cowell, 1976; Cowell and Hartmann-Goldstein, 1980) that band region 3D1-E2, adjacent to the breakpoint, contained less DNA than the homologous non-translocated region whereas the neighbouring 3C1-10 region contained more DNA than its non-translocated counterpart. In the nuclei selected for measurement the translocated X chromosome was morphologically euchromatic, but both regions undergo heterochromatisation in other nuclei within the same salivary gland. To explore the relationship between changes in DNA content and heterochromatisation, the effect on DNA content of two known modifiers of heterochromatisation has now been studied. Larvae cultured at 15 degrees C, which exhibit more heterochromatisation than those grown in 25 degrees C, have the same relative DNA contents as at the higher temperature. The addition of a Y chromosome markedly reduced heterochromatisation; in XXY larvae there was no difference between the DNA contents of translocated and non-translocated 3D1-E2 regions, and in region 3C1-10 the percentage excess of DNA in the translocated homolgue was approximately double that found in XX larvae. The relationship between replication behaviour and compaction suggested by these results is discussed.

Reduced DNA polytenization of a minichromosome region undergoing position-effect variegation in Drosophila

“…Although small reductions in DNA content were reported previously in some cases (Schultz, 1941;Ananiev and Gvozdev, 1974;Cowell and Hartmann-Goldstein, 1980;Kornher and Kaufman, 1986) other workers detected no evidence for changes in copy number (Cole and Sutton, 1941;Henikoff, 1961;Rushlow et al, 1984). Most measurements were made at an unknown distance from the inducing breakpoint.…”

“…Although local changes in the appearance of variegating polytene chromosomes are easily seen (Prokofyeva-Belgovskaya, 1939;Schultz and Caspersson, 1939) only small changes in DNA copy number, at most 2-to 3-fold, have been reported (Cowell and Hartmann-Goldstein, 1980;Kornher and Kaufman, 1986). After correcting for changes in chromatin structure, Henikoff (1981) detected no differences in the polytenization of a variegating heat shock puff.…”

The genetics of position — effect variegation modifying loci inDrosophila melanogaster

“…The compact packaging of heterochromatin is extended into the adjoining euchromatic region resulting in repression of the affected loci. Modifiers such as temperature, amount of Y chromosome heterochromatin and mutations display identical effects on phenotypic variegation and heterochromatinization at the chromosomal level (Hartmann-Goldstein 1967;Cowell and Hartmann-Goldstein 1980;Reuter et al 1982a;Zhimulev et al 1986). Variegated mutant expression of the affected genes reflects not only high variability but also clonal initiation of heterochromatinization (Janning 1970).…”

Characteristics of SP600125 Induced Tetraploid Cells in Comparison With Diploid and Tetraploid Cells of Fish

“…Tetraploid is an organism with four chromosome groups in somatic cells. It has been shown that the tetraploid cells had chromatin instability owing to the difficulties in dividing genomes with double number of centrosomes and chromosomes ( Cowell 1980 ; Mayer and Aguilera, 1990 ; Fujiwara et al, 2005 ; Margolis 2005 ; Storchova et al, 2006 ; Coward and Harding 2014 ). In general, an increasing nuclear DNA content has important effects on gene expression in cells ( Hancock, Martin, and Lelchuk 1993 ).…”