Determinants of Drosophila zw10 protein localization and function.

We have examined several issues concerning how the Drosophila l(1)zw10 gene product functions to ensure proper chromosome segregation. (a) We have found that in zw10 mutant embryos and larval neuroblasts, absence of the zw10 protein has no obvious effect on either the congression of chromosomes to the metaphase plate or the morphology of the metaphase spindle, although many aberrations are observed subsequently in anaphase. This suggests that activity of the zw10 protein becomes essential at anaphase onset, a time at which the zw10 protein is redistributed to the kinetochore region of the chromosomes. (b) The zw10 protein appears to bind to kinetochores in mitotically arrested cells, eventually accumulating to high levels within the chromosome mass. Our results imply that zw10 may act as part of a novel feedback pathway that normally renders sister chromatid separation dependent upon spindle integrity. (c) The localization of zw10 protein is altered by two mitotic mutations, rough deal and abnormal anaphase resolution, that specifically disrupt anaphase. These findings indicate that the zw10 protein functions as part of a multicomponent mechanism ensuring proper chromosome segregation at the beginning of anaphase.