2 PROTEINS THAT CYCLE ASYNCHRONOUSLY BETWEEN CENTROSOMES AND NUCLEAR-STRUCTURES - DROSOPHILA CP60 AND CP190

Both the nucleus and the centrosome are complex, dynamic structures wh ose architectures undergo cell cycle-specific rearrangements, CP190 an d CP60 are two Drosophila proteins of unknown function that shuttle be tween centrosomes and nuclei in a cell cycle-dependent manner, These t wo proteins are associated in vitro, and localize to centrosomes in a microtubule independent manner, We injected fluorescently labeled, bac terially expressed CP190 and CP60 into living Drosophila embryos and f ollowed their behavior during the rapid syncytial blastoderm divisions (nuclear cycles 10-13), Using quantitative 3-D wide-held fluorescence microscopy, we show that CP190 and CP60 cycle between nuclei and cent rosomes asynchronously with the accumulation of CP190 leading that of CP60 both at centrosomes and in nuclei, During interphase, CP190 is fo und in nuclei, Immediately following nuclear envelope breakdown, CP190 localizes to centrosomes where it remains until telophase, thereafter accumulating in reforming nuclei. Unlike CP190, CP60 accumulates at c entrosomes primarily during anaphase, where it remains into early inte rphase, During nuclear cycles 10 and 11, CP60 accumulates in nuclei si multaneous with nuclear envelope breakdown, suggesting that CP60 binds to an unknown nuclear structure that persists into mitosis, During nu clear cycles 12 and 13, CP60 accumulates gradually in nuclei during in terphase, reaching peak levels just before nuclear envelope breakdown, Once in the nucleus, both CP190 and CP60 appear to form fibrous intra nuclear networks that remain coherent even after nuclear envelope brea kdown, The CP190 and CP60 networks do not co-localize extensively with each other or with DNA, This work provides direct evidence, in living cells, of a coherent protein network that may represent a nuclear ske leton.