Nucleolar association of pEg7 and XCAP-E, two members ofXenopus laeviscondensin complex in interphase cells

Abstract

Cell cycle dynamics and localization of condensins — multiprotein complexes involved in late stages of mitotic chromosome condensation —were studied in Xenopus laevis XL2 cell line. Western blot analysis of synchronized cells showed that the ratio of levels of both pEg7 and XCAP-E to β-tubulin levels remains almost constant from G1 to M phase. pEg7 and XCAP-E were localized to the mitotic chromosomes and were detected in interphase nuclei. Immunostaining for condensins and nucleolar proteins UBF,fibrillarin and B23 revealed that both XCAP-E and pEg7 are localized in the granular component of the nucleolus. Nucleolar labeling of both proteins is preserved in segregated nucleoli after 6 hours of incubation with actinomycin D (5 mg/ml), but the size of the labeled zone was significantly smaller. The data suggest a novel interphase function of condensin subunits in spatial organization of the nucleolus and/or ribosome biogenesis.

Diverse Mitotic and Interphase Functions of Condensins in Drosophila

“…This contrasts with previously published results in which the barr L305 allele was shown to suppress 5F24(25,2) variegation in adult female progeny (Lupo et al 2001) but is nonetheless consistent with more recent findings concerning the lack of any discernible effect of dcap-g mutations on regulation of gene expression by the Fab-7 Polycombgroup response element (Dej et al 2004). However, as the w m4h inversion places the white gene near the bobbed multicopy rDNA array within pericentric heterochromatin, it is possible that the PEV assay performed with w m4h flies may be more sensitive to mutations affecting condensin components if such proteins are enriched at rDNA loci as in other species (Freeman et al 2000;Cabello et al 2001;Bhalla et al 2002;Uzbekov et al 2003;D'Amours et al 2004;Wang et al 2004) and since various condensin proteins in Drosophila have been shown to be enriched at mitotic centromeres (Steffensen et al 2001;Savvidou et al 2005). To evaluate whether the effects of condensin mutations on PEV were specific to particular chromosomal regions, additional crosses were performed between selected alleles and flies carrying transgenic white reporter genes at different chromosomal loci.…”

Distinct functions of condensin I and II in mitotic chromosome assembly

“…Condensin II and I associate with chromosomes in prophase and prometaphase, respectively Based on immunofluorescence (IF) microscopy experiments, condensin I has been reported to be located in the nucleus of interphase cells (Cabello et al, 2001;Uzbekov et al, 2003); however, the complex has also been found to be cytoplasmic (Ball et al, 2002;Cabello et al, 2001;Maeshima and Laemmli, 2003;Schmiesing et al, 2000;Steffensen et al, 2001;Uzbekov et al, 2003). The latter finding was surprising considering the genetic evidence that condensin subunits are required for chromosome condensation in prophase (Hagstrom et al, 2002;Kaitna et al, 2002;Hudson et al, 2003), i.e.…”

DrosophilaCAP-D2 is required for condensin complex stability and resolution of sister chromatids

“…Differential localisation of condensin subunits during interphase in Drosophila suggests that CAP-D2 may be sequestered away from SMCs to regulate activity or may be utilized for a function other than that required of other condensin subunits during interphase. It has recently been shown in Xenopus that CAP-D2 (pEg7) along with SMC2 (XCAP-E) localise in the granular compartment of the nucleolus, suggesting that these subunits may be involved in nucleolar organisation and/or ribosome biogenesis (Uzbekov et al, 2003). In S. cerevisiae, the CAP-D2 orthologue Ycs4 is nuclear during interphase, implicated in suppressing inter-repeat rDNA recombination and required for silencing at the mating-type loci (Bhalla et al, 2002).…”