Condensin I binds chromatin early in prophase and displays a highly dynamic association with Drosophila mitotic chromosomes.
The condensed state of mitotic chromosomes is crucial for faithful genome segregation. Key factors implicated in the formation of mitotic chromosomes are the condensin I and II complexes. In Drosophila, condensin I appears to play a major role in mitotic chromosome organization. To analyze its dynamic behavior, we expressed Barren, a condensin I non-Structural Maintenance of Chromosomes subunit, as a fully functional enhanced green fluorescent protein (EGFP) fusion protein in the female and followed it during early embryonic divisions. We find that, in Drosophila, Barren-EGFP associates with chromatin early in prophase concomitantly with the initiation of chromosome condensation. Barren-EGFP loading starts at the centromeric region from where it spreads distally reaching maximum accumulation at metaphase/early anaphase. Fluorescence Recovery After Photobleaching analysis indicates that most of the bound protein exchanges rapidly with the cytoplasmic pool during prometaphase/metaphase. Taken together, our results suggest that in Drosophila, condensin I is involved in the initial stages of chromosome condensation. Furthermore, the rapid turnover of Barren-EGFP indicates that the mechanism by which condensin I promotes mitotic chromosome organization is inconsistent with a static scaffold model.
Oliveira
Raquel A
RA
Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
Heidmann
Stefan
S
Sunkel
Claudio E
CE
D000251:Adenosine Triphosphatases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D018797:Cell Cycle Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism*; D002875:Chromosomes / Q000378:metabolism* / Q000648:ultrastructure; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000737:chemistry / Q000196:embryology* / Q000235:genetics; D029721:Drosophila Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D008938:Mitosis; D046912:Multiprotein Complexes / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011418:Prophase
C103227:Barr protein, Drosophila; D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D046912:Multiprotein Complexes; C108312:condensin complexes; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D000251:Adenosine Triphosphatases