Genetic and molecular analysis of gene trans-inactivation caused by homologous eu-heterochromatic chromosome rearrangement in Drosophila melanogaster

Trans-inactivation: Repression in a wrong place

“…In(2)A4 induces robust and widespread trans-inactivation of mini-white reporter genes located on the homologous, non-rearranged chromosome as well as of genes in cis, located near the new eu-heterochromatin border. [18][19][20] Trans-inactivation effects in In (2)A4 and bw D are similar in many aspects, apparently reflecting common properties of trans-inactivation process in Drosophila. FISH data show that, like in the bw D case, the normal chromosome and the inversion are somatically paired, and the region of the inversion near the new eu-heterochromatin boundary and the homologous region of the normal chromosome are dragged into the heterochromatic nuclear compartment.…”

“…These include rearrangements with breakpoints near or inside the brown gene, such as the brown Dominant (bw D ) allele, 15,16 mini-white-containing transgenes over the PEV-inducing rearrangements 17 and the In(2)A4 inversion. [18][19][20] The beststudied trans-inactivation-inducing rearrangement is bw D allele, which emerged as a result of insertion of 1.6 Mb of AAGAG satellite into the coding region of the brown gene. 21 This allele can repress the wild-type brown gene on the opposite chromosome, as well as reporter genes inserted near the brown.…”

“…FISH data show that, like in the bw D case, the normal chromosome and the inversion are somatically paired, and the region of the inversion near the new eu-heterochromatin boundary and the homologous region of the normal chromosome are dragged into the heterochromatic nuclear compartment. 20 The dragging of a reporter gene into the heterochromatin correlates with its repression at the single-cell level, pointing to the dragging process as the direct cause of trans-inactivation. 19 The effects of genetic modifiers of PEV on In(2)A4-induced transinactivation resemble that at the bw D locus: Su(var)2-5 (HP1a) and Su(var)3-7 strongly suppress the inactivation while Su(var)3-9 HKMT mutations produce no effect.…”

“…E is the region near the histone genes cluster, no repression observed here, and F is the "island" of trans-inactivation after the histone genes cluster. Below the linear map, the putative organization of the loop of paired chromosomes in the nuclear space is shown according to a combination of FISH data [18][19][20] and polytene chromosomes arrangement. The light green is euchromatin; the brown gradient zone is HP1a-stained pericentromeric heterochromatin compartment.…”

The Differences BetweenCis- andTrans-Gene Inactivation Caused by Heterochromatin inDrosophila

“…The heterochromatinization of the trans-inactivated transgene probably induces the accumulation of HP1a on the opposite site on the homologous chromosome. Results of ChIP experiments demonstrate that the trans-inactivated transgene binds HP1a and that autonomous heterochromatinization of the transgene could induce the accumulation of HP1a on the opposite chromosome.Trans-Inactivation and the nuclear position of the histone clusterThe small, detached heterochromatin block in the A4 chromosome tends to conjugate with the pericentromeric heterochromatin in A4/A4 flies and is able to drag regions of somatically paired normal chromosome (in A4/+ flies) into the heterochromatic nuclear compartment (Abramov et al 2011;Lavrov et al 2013; unpublished data). Inversion A4 produces a peculiar pattern of mini-white transgene transinactivation along the chromosome: repression occurs on both sides of the histone gene cluster, while several transgenes (21396, 21432, 16407, and 12761) (Figure 3, region D) located close to the cluster show no mini-white repression.…”