MITOTIC PHOSPHOEPITOPES ARE EXPRESSED IN KC CELLS, NEUROBLASTS AND ISOLATED CHROMOSOMES OF DROSOPHILA-MELANOGASTER

The progression of cells from metaphase to anaphase is thought to be r egulated by a checkpoint that delays entry into anaphase until all chr omosomes reach a stable hi-polar attachment at the metaphase plate, Pr evious work has suggested that the 3F3/2 kinetochore phosphoepitopes a re involved in this checkpoint system, We show that the 3F3/2 centrome re phosphoepitopes are present in Kc cells, third instar larval neurob lasts and isolated chromosomes of Drosophila melanogaster. In tissue c ulture cells and neuroblasts isolated from third instar larvae, centro mere labelling is detected from early prophase to the metaphase-anapha se transition hut absent once cells enter anaphase, During anaphase, t he antibody stains the spindle mid zone and during telophase the midbo dy is labelled until cells separate, In both cell types, the 3F3/2 ant ibody stains the centrosome from prophase to late telophase, The 3F3/2 staining is retained in Kc cells and third instar larval neuroblasts arrested at the prometaphase state with microtubule inhibitors. Also, two mitotic mutants that show abnormal spindle morphology retain the c entromere labelling in a metaphase-like configuration, suggesting that they activate the metaphase-anaphase checkpoint, Finally, mitotic chr omosomes isolated in the presence of a phosphatase inhibitor show phos phoepitopes at the primary constriction on the surface of each chromat id, however, chromosomes isolated in the absence of a phosphatase inhi bitor do not, Incubation of these chromosomes with ATP causes the reph osphorylation of the phosphoepitopes at the centromere.