A selective block of nuclear actin export stabilizes the giant nuclei of Xenopus oocytes

@article{Bohnsack2006ASB,
  title={A selective block of nuclear actin export stabilizes the giant nuclei of Xenopus oocytes},
  author={Markus T. Bohnsack and Theis St{\"u}ven and Christa Kuhn and Volker C. Cordes and Dirk G{\"o}rlich},
  journal={Nature Cell Biology},
  year={2006},
  volume={8},
  pages={257-263}
}
Actin is a major cytoskeletal element and is normally kept cytoplasmic by exportin 6 (Exp6)-driven nuclear export. Here, we show that Exp6 recognizes actin features that are conserved from yeast to human. Surprisingly however, microinjected actin was not exported from Xenopus laevis oocyte nuclei, unless Exp6 was co-injected, indicating that the pathway is inactive in this cell type. Indeed, Exp6 is undetectable in oocytes, but is synthesized from meiotic maturation onwards, which explains how… 

Nuclear actin depolymerization in transcriptionally active avian and amphibian oocytes leads to collapse of intranuclear structures

In experiments with the actin depolymerizing drugs cytochalasin D and latrunculin A, it was showed that disassembly of nuclear actin polymers led to chromosome condensation and their transportation to a limited space within the oocyte nucleus, strongly resembled the process of karyosphere formation during oocyte growth.

Chromatin tethering to the nuclear envelope by nuclear actin filaments: a novel role of the actin cytoskeleton in the Xenopus blastula

The Xenopus egg extract is devised and it is found that F-actin accumulates primarily at the sub-nuclear membranous region and is essential to maintain chromatin binding to the nuclear envelope in well-developed nuclei and contributes to chromosome alignment on the mitotic spindle at the following M phase.

Stabilization of actin filaments prevents germinal vesicle breakdown and affects microtubule organization in Xenopus oocytes

In Xenopus oocytes, extremely giant nuclei, termed germinal vesicles, contain a large amount of actin filaments most likely for mechanical integrity. Here, we show that microinjection of phalloidin,

Fascin regulates nuclear actin during Drosophila oogenesis

The novel finding that Drosophila oogenesis, or follicle development, is a model for studying the structure, regulation, and function of nuclear actin is established and Fascin is identified as a novel regulator ofnuclear actin.

Nuclear export of actin: A biochemical and structural perspective

A new single-step protocol for purification of profilin*β/γ-actin complexes from cytoplasmic extracts, which enabled us to purify a stable actin export complex and crystallize the actin nuclear export complex, which was successfully crystallized.

Active maintenance of nuclear actin by importin 9 supports transcription

It is demonstrated that cytoplasmic and nuclear actin pools are dynamically connected and the nuclear import and export mechanisms of actin are identified, which suggest an active transport mechanism in both directions.

Multiple Pools of Nuclear Actin

This work uses Drosophila oogenesis, that is, follicle development, to characterize nuclear actin, and finds that three different reagents—DNase I, anti‐actin C4, and anti-actin AC15—recognize distinct pools of nuclearActin.

Nuclear actin polymerization is required for transcriptional reprogramming of Oct4 by oocytes.

This is the first report showing that naturally stored actin in an oocyte nucleus helps transcriptional reprogramming in a polymerization-dependent manner, and an actin signaling protein, Toca-1, enhances Oct4 reactivation by regulating nuclear actin polymerization.

The nuclear F-actin interactome of Xenopus oocytes reveals an actin-bundling kinesin that is essential for meiotic cytokinesis

The data are consistent with the notion that NabKin/KIF14 directly link microtubules with F‐actin and that such link is essential for cytokinesis, which was previously shown to be essential for somatic cell division.

Steady‐state nuclear actin levels are determined by export competent actin pool

It is found that in cells growing under normal growth conditions, the levels of nuclear actin vary considerably from cell to cell, and the ratio of nuclear to cytoplasmic fluorescence intensity, but not nuclear shape, size, cy toplasm size, or their ratio, correlates negatively with both import and export rate of actin.
...

References

SHOWING 1-10 OF 47 REFERENCES

Exportin 6: a novel nuclear export receptor that is specific for profilin·actin complexes

Exportin 6 (Exp6) is identified as a novel family member from higher eukaryotes and it is shown that it mediates nuclear export of profilin·actin complexes and functions not only as the nucleotide exchange factor for actin, but also as a cofactor of actin export.

Diffusible and bound actin in nuclei of xenopus laevis oocytes

Actin in the nucleus: what form and what for?

Mediators of nuclear protein import target karyophilic proteins to pore complexes of cytoplasmic annulate lamellae.

It is demonstrated that annulate lamellae can represent distinct sites within the cytoplasm of transient accumulation of nuclear proteins and that the AL pore complex shares functional binding properties with the NPC.

Confocal microscopy of F-actin distribution in Xenopus oocytes

Disruption of F-actin in stage VI oocytes with cytochalasin resulted in distortion and apparent rotation of the GV in the animal hemisphere, suggesting that actin plays a role in maintaining the polarised organisation of amphibian oocytes.

Actin- and protein-4.1-containing filaments link nuclear pore complexes to subnuclear organelles in Xenopus oocyte nuclei

It is suggested that protein 4.1 and actin contribute to the structure of a network of heterogeneous filaments that link nuclear pore complexes to subnuclear organelles, and possible functions for PLFs in nuclear assembly and intranuclear traffic are discussed.

Exportin 7 defines a novel general nuclear export pathway

It is shown that RanBP16 exports p50RhoGAP from the nucleus and thereby confines this activity to the cytoplasm, and it is demonstrated that Exp7‐dependent nuclear export signals differ fundamentally from the leucine‐rich, CRM1‐dependent ones: First, they are not just short linear sequences, but instead include folded motifs and basic residues are critical for Exp7 recruitment.

Actin is part of pre-initiation complexes and is necessary for transcription by RNA polymerase II

A fundamental role for actin in the initiation of transcription by RNA polymerase II is suggested after it was demonstrated that antibodies directed against β-actin, but not muscle actin, inhibited transcription in vivo and in vitro.