A Distinct Type of Heterochromatin at the Telomeric Region of the Drosophila melanogaster Y Chromosome

Abstract

Heterochromatin assembly and its associated phenotype, position effect variegation (PEV), provide an informative system to study chromatin structure and genome packaging. In the fruit fly Drosophila melanogaster, the Y chromosome is entirely heterochromatic in all cell types except the male germline; as such, Y chromosome dosage is a potent modifier of PEV. However, neither Y heterochromatin composition, nor its assembly, has been carefully studied. Here, we report the mapping and characterization of eight reporter lines that show male-specific PEV. In all eight cases, the reporter insertion sites lie in the telomeric transposon array (HeT-A and TART-B2 homologous repeats) of the Y chromosome short arm (Ys). Investigations of the impact on the PEV phenotype of mutations in known heterochromatin proteins (i.e., modifiers of PEV) show that this Ys telomeric region is a unique heterochromatin domain: it displays sensitivity to mutations in HP1a, EGG and SU(VAR)3-9, but no sensitivity to Su(z)2 mutations. It appears that the endo-siRNA pathway plays a major targeting role for this domain. Interestingly, an ectopic copy of 1360 is sufficient to induce a piRNA targeting mechanism to further enhance silencing of a reporter cytologically localized to the Ys telomere. These results demonstrate the diversity of heterochromatin domains, and the corresponding variation in potential targeting mechanisms.

Direct interrogation of the role of H3K9 in metazoan heterochromatin function

“…Recent studies have illuminated the diversity of heterochromatin that exists throughout the genome (Haynes et al 2007;Riddle et al 2011;Wang et al 2014). These different types of heterochromatin may rely on H3K9me to differing extents.…”

Telomere fusion in Drosophila: The role of subtelomeric chromatin

“…Recent studies have shown that subtelomeric heterochromatin can silence genes embedded into the adjacent HTT array. 38 This effect is reminiscent of PEV and suggests that some heterochromatic proteins spread into the HTT array, impairing the expression of the inserted transgenes. These findings open the way to future studies aimed at the identification of the factors that modify the specific sensitivity of Ha-telomeres to the loss of peo function.…”

“…In contrast, the expression of transgenes inserted into the YS HTT arrays is enhanced by mutation in typical PEV suppressor genes. 38 These results suggest that the chromatin of the HTTs juxtaposed to heterochromatin shares some properties with constitutive heterochromatin and is different from the autosomal HTT and TAS chromatin types (Fig. 1).…”

“…w C transgenes inserted into the HTTs arrays of the 2L, 3L and 3R arms are not silenced, whereas the expression w C transgenes within the 4R or YS HTTs is impaired, leading to a variegated eye color phenotype. 37,38 In addition, w C transgenes embedded into the TAS and the YS HTT arrays respond differently to genetic modifiers. The effects on TPE of TAS-associated transgenes are ameliorated by mutation in a specific set of genes, most of which have no effect on PEV (see ref.…”

Two‐step cavitation in semi‐crystalline polymer during stretching at temperature below glass transition

“…INTRODUCTION Cavitation was observed in many semicrysalline polymers, such as polyethylene (PE), [1][2][3][4][5][6][7][8][9] isotactic polypropylene (iPP), [10][11][12][13][14][15][16][17][18] and poly(1-butene) (P1B), [19][20][21][22] when they underwent tensile deformation. The formation of cavities was generally accompanied by obvious macroscopic whitening of the stretched samples due to the significant difference in refractive index between the cavities and polymer matrix.…”