Characterization of phalloidin-negative nuclear actin filaments in U2OS cells expressing cytoplasmic actin-EGFP

Akira Nagasaki*, Kaoru Katoh, Masamichi Hoshi, Motomichi Doi, Chikashi Nakamura, Taro Q.P. Uyeda

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Actin is a major structural component of the cytoskeleton in eukaryotic cells, including fungi, plants, and animals, and exists not only in the cytoplasm as cytoskeleton but also in the nucleus. Recently, we developed a novel actin probe, β-actin-EGFP fusion protein, which exhibited similar monomeric to filamentous ratio as that of endogenous actin, in contrast to the widely used EGFP-β-actin fusion protein that over-assembles in cells. Unexpectedly, this novel probe visualized an interconnected meshwork of slightly curved beam-like bundles of actin filaments in the nucleus of U2OS cells. These structures were not labeled with rhodamine phalloidin, Lifeact-EGFP or anti-actin antibodies. In addition, immunofluorescence staining and expression of cofilin-EGFP revealed that this nuclear actin structures contained cofilin. We named these actin filaments as phalloidin-negative intranuclear (PHANIN) actin filaments. Since PHANIN actin filaments could not be detected by general detection methods for actin filaments, we propose that PHANIN actin filaments are different from previously reported nuclear actin structures.

Original languageEnglish
Pages (from-to)317-330
Number of pages14
JournalGenes to Cells
Issue number5
Publication statusPublished - 2022 May


  • GFP
  • GFP-actin fusion protein
  • actin
  • actin probe and cofilin
  • nuclear actin
  • phalloidin

ASJC Scopus subject areas

  • Genetics
  • Cell Biology


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