The Drosophila EAST protein associates with a nuclear remnant during mitosis and constrains chromosome mobility.

Drosophila EAST protein associates with an interior nonchromosomal compartment of the interphase nucleus. Because overexpression of east can dramatically alter nuclear architecture we investigated a potential role for EAST in changing chromosome organization during the cell cycle. Following nuclear envelope breakdown, EAST remains enriched in the mitotic remnant of the interphase nucleus until the onset of anaphase. Loss of east expression affects the accuracy of division cycles. In female meiosis, east mutations lead to abnormal segregation of nonexchange chromosomes. During the syncytial nuclear cycles, increased frequency of mitotic errors leads to the depletion of surface nuclei. In the post-syncytial cell cycles, abnormal congression of chromosomes in prometaphase delays the onset of anaphase. Loss of east expression also results in abnormal chromosome morphology in male meiosis. We propose that EAST constitutes a component of a nucleoskeleton that helps to constrain the mobility of chromosomes in interphase, mitosis and meiosis.