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EMBO reports 9, 5, 440–445 (2008)
doi:10.1038/embor.2008.32
AOP Published online: 28 March 2008
'Insulator bodies' are aggregates of proteins but not of insulators
Anton Golovnin1, 2, Larisa Melnikova1, Ilya Volkov3, Margarita Kostuchenko1, Alexander V Galkin4 & Pavel Georgiev1
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1 Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov Street, Moscow 119334, Russia
2 Centre for Medical Studies of Oslo University, 34/5 Vavilov Street, Moscow 119334, Russia
3 Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 32 Vavilov Street, Moscow 119991, Russia
4 Department of Molecular Immunogenetics of Cancer, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov Street, Moscow 119334, Russia
To whom correspondence should be addressed
Pavel Georgiev Tel: +7 499 1359734; Fax: +7 499 1354105; E-mail: georgiev_p@mail.ru
Received 7 September 2007; Accepted 8 February 2008; Published online 28 March 2008.
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Abstract
Chromatin insulators are thought to restrict the action of enhancers and silencers. The best-known insulators in Drosophila require proteins such as Suppressor of Hairy wing (Su(Hw)) and Modifier of mdg4 (Mod(mdg4)) to be functional. The insulator-related proteins apparently colocalize as nuclear speckles in immunostained cells. It has been asserted that these speckles are 'insulator bodies' of many Su(Hw)–insulator DNA sites held together by associated proteins, including Mod(mdg4). As we show here using flies, larvae and S2 cells, a mutant Mod(mdg4) protein devoid of the Q-rich domain supports the function of Su(Hw)-dependent insulators and efficiently binds to correct insulator sites on the chromosome, but does not form or enter the Su(Hw)-marked nuclear speckles; conversely, the latter accumulate another (C-truncated) Mod(mdg4) mutant that cannot interact with Su(Hw) or with the genuine insulators. Hence, it is not the functional genomic insulators but rather aggregated proteins that make the so-called 'insulator bodies'.
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