Increased expression ofDrosophilaSu(var)3-7 triggers Su(var)3-9-dependent heterochromatin formation

Abstract

The Su(var)3-7 protein is essential for fly viability, and several lines of evidence support its key importance in heterochromatin formation: it binds to pericentric heterochromatin, it potently suppresses variegation and it interacts with HP1. However, the mode of action of Su(var)3-7 is poorly understood. Here we investigate in vivo the consequences of increased Su(var)3-7 expression on fly viability and chromatin structure. A large excess of Su(var)3-7 induces lethality, whereas lower doses permit survival and cause spectacular changes in the morphology of polytene chromosomes in males, and to a lesser extent in females. The male X is always the most affected chromosome: it becomes highly condensed and shortened, and its characteristic banding pattern is modified. In addition, Su(var)3-7 was found over the complete length of all chromosomes. This event coincides with the appearance of heterochromatin markers such as histone H3K9 dimethylation and HP1 at many sites on autosomes and, more strikingly, on the male X chromosome. These two features are strictly dependent on the histone-methyltransferase Su(var)3-9, whereas the generalised localisation of Su(var)3-7 is not. These data provide evidence for a dose-dependent regulatory role of Su(var)37 in chromosome morphology and heterochromatin formation. Moreover they show that Su(var)3-7 expression is sufficient to induce Su(var)3-9-dependent ectopic heterochromatinisation and suggest a functional link between Su(var)3-7 and the histone-methyltransferase Su(var)3-9

Heterochromatin remodeling by CDK12 contributes to learning in Drosophila

“…Consistent with previous reports that the X chromosome is a preferential target for heterochromatin enrichment (12,16), the accumulation of HP1 induced by CDK12 depletion was prominent on the X chromosome marked by acetylation of histone H4 on Lys16 in males ( Fig. 2A).…”

“…In this study, we have shown that the depletion of CDK12 induces heterochromatin accumulation within euchromatic arms, particularly on the X chromosome. Previous reports show that overexpression of Su(var)3-7 induces ectopic heterochromatin formation on the euchromatic arms, with preferential enrichment of HP1 and H3K9me2 in the male X chromosome (16). This pattern is associated with the dosage compensation complex, and it is distinct from CDK12 depletion-triggered heterochromatin enrichment.…”

A male‐specific effect of dominant‐negative Fos

“…This demonstrates an effect on female gene expression. Third, mutations shown to affect chromosome structure can impact dosage compensation (Delattre et al, 2004;Spierer et al, 2008), similar to the Fos bZip effect proposed here.…”

Misregulation of Sex-Lethal and Disruption of Male-Specific Lethal Complex Localization in Drosophila Species Hybrids

“…Interestingly, when the same cross was made using the Lhr D. simulans strain, the male X chromosome exhibited a bloated and diffuse appearance (Figure 2) in contrast to the same direction of cross without an attached X ( Figure 1D). This bloated type of chromosome morphology has also been observed in numerous mutant male larvae, for example, with ISWI (Corona et al 2002), HP1, and Su(var)3-7 (Delattre et al 2004;Spierer et al 2005) among others (see discussion in Pal Bhadra et al 2005). Whether there is a relationship to these defects is not known.…”