Histochemistry and Cell Biology

, Volume 138, Issue 3, pp 515–530 | Cite as

Nucleoplasmic/nucleolar translocation and identification of a nuclear localization signal (NLS) in Dictyostelium BAF60a/SMARCD1 homologue Snf12

  • Andrew Catalano
  • Danton H. O’Day
Original Paper


Dictyostelium is a model eukaryote for the study of several cellular processes; however, comparatively little is known about its nucleolus. Identification of nucleolar proteins is key to understanding this nuclear subcompartment, but only four have been identified in Dictyostelium. As discussed in this article, a potential relationship between nucleolar NumA1 and BAF60a/SMARCD1 suggested BAF60a may also reside in the nucleolus. Here, we identify BAF60a homologue Snf12 as the fifth nucleolar protein in Dictyostelium. Immunolocalization experiments demonstrate that Snf12 is nucleoplasmic, but translocates to nucleoli upon actinomycin-D-induced transcription inhibition (0.05 mg/mL, 4 h). Translocation was accompanied by a microtubule-independent protrusion of nucleolar Snf12 regions from the nucleus followed by detection of Snf12 in cytoplasmic circles for at least 48 h. Residues 372KRKR375 are both necessary and sufficient for nucleoplasmic localization of Snf12 and represent a functional nuclear localization signal (NLS), similar to recently identified NLSs in other Dictyostelium proteins. Since nucleolar and nucleoplasmic proteins redistribute during mitosis, we investigated Snf12 dynamics during this time. Dictyostelium undergoes closed mitosis, meaning its nuclear envelope remains intact. Despite this, during metaphase and anaphase Snf12 redistributed throughout the cytoplasm before reaccumulating in the nucleus during telophase, unlike the previously reported nucleoplasmic redistribution of nucleolar NumA1. The nuclear exit of Snf12 was independent of its putative nuclear export signal and not inhibited by exportin inhibition, suggesting that the redistribution of nuclear proteins during mitosis in Dictyostelium is mediated by other mechanisms. Snf12 is the second Dictyostelium nucleolar protein for which its dynamics during mitosis have been investigated.


Snf12 Nucleoplasm Nucleolus Nuclear localization signal Dictyostelium Actinomycin-D 





Nuclear localization signal


Nucleolar localization signal





This work was supported by the Natural Sciences and Engineering Research Council of Canada (DHO’D; A6807).

Supplementary material

418_2012_973_MOESM1_ESM.tif (697 kb)
Supplementary Fig. 1 N-GFP-Snf12 and C-GFP-Snf12 localize to spore nuclei. Cells expressing either GFP alone, N-GFP-Snf12 (not shown), or C-GFP-Snf12 were allowed to develop into fruiting bodies. Both N-GFP-Snf12 and C-GFP-Snf12 were detected in the nucleus of spore cells whereas GFP alone was detected throughout the entire spore, as demonstrated by colocalization with calcofluor. No fluorescence was detected in stalk cells. Merged image shows overlay of GFP fluorescence (GFP fluor.; green) and calcofluor (blue). Scale bar represents 2 μm. (TIFF 697 kb)


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  1. 1.Department of Cell and Systems BiologyUniversity of TorontoTorontoCanada
  2. 2.Department of BiologyUniversity of Toronto at MississaugaMississaugaCanada

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