Actin-dependent intranuclear repositioning of an active gene locus in vivo

Abstract

Although bulk chromatin is thought to have limited mobility within the interphase eukaryotic nucleus, directed long-distance chromosome movements are not unknown. Cajal bodies (CBs) are nuclear suborganelles that nonrandomly associate with small nuclear RNA (snRNA) and histone gene loci in human cells during interphase. However, the mechanism responsible for this association is uncertain. In this study, we present an experimental system to probe the dynamic interplay of CBs with a U2 snRNA target gene locus during transcriptional activation in living cells. Simultaneous four-dimensional tracking of CBs and U2 genes reveals that target loci are recruited toward relatively stably positioned CBs by long-range chromosomal motion. In the presence of a dominant-negative mutant of β-actin, the repositioning of activated U2 genes is markedly inhibited. This supports a model in which nuclear actin is required for these rapid, long-range chromosomal movements.

Coilin: The first 25 years

“…61,69 CBs may be assembled on or transported toward active snRNA genes. 70 This transcription-dependent contact between snRNA genes and CBs was recently confirmed by the finding that coilin ChIP signals on snRNA genes is cell cycle specific, with the highest signal in S-phase when snRNA genes are actively transcribed. 33 Similarly, coilin binding to U7 snRNA brings histone genes to a close proximity of CBs.…”

Direct actin binding to A- and B-type lamin tails and actin filament bundling by the lamin A tail

“…The first site, AB-1, is shared and conserved in all lamins whereas the second site, AB-2, is unique to lamin A. F-actin bundles were detected by rhodamine-phalloidin labeling and by TEM imaging, suggesting lamin-mediated bundling was not an artifact of centrifugation in the high-and low-speed pelleting assays. These findings suggest potential concerted mechanisms for pathways that are known to require both polymerizable actin and A-type lamins, such as mRNA export, [36][37][38][39] intranuclear chromatin movement 40,41 and transcription. 5,[42][43][44] Although nuclei lack phalloidin-stainable F-actin, approximately 20% of actin in the nucleus is found in alternative polymeric state(s).…”

Induction of HoxB Transcription by Retinoic Acid Requires Actin Polymerization

“…A Nuclear-Targeted Dominant Negative Actin Mutant Blocks HoxB Induction by RA To further demonstrate a direct role of actin polymerization in gene regulation, we used two actin mutant constructs that contain a nuclear localization signal (NLS) that allows the nuclear localization of the mutant actin forms (Chuang et al, 2006;Dundr et al, 2007). Of these, mRFP-NLS-G13R is deficient in actin polymerization and blocks F-actin polymerization in a dominant-negative manner (Chuang et al, 2006), whereas mRFP-NLS-S14C favors nuclear actin polymerization (Chuang et al, 2006).…”