Accurate segregation of chromosomes during mitosis and meiosis is crucial for viability. The replicated copies of the each chromosome, the sister chromatids, must be physically attached to orient and bind to the microtubules of the spindle so that they segregate to opposite sides of the cell during division. The sister chromatids also must condense and resolve from each other to separate completely when they move to the poles of the spindle in anaphase. The cohesin protein complex is essential for sister-chromatid cohesion and the condensin complex is needed for resolution and condensation. Another protein complex, the chromosome passenger complex (CPC), also is involved in condensation as well as spindle attachment and stability and cytokinesis. The Drosophila MEI-S332 protein, isolated with previous NSF support, is the founding member of the Shugoshin family of proteins, conserved to humans, that plays a critical role in mitotic and meiotic chromosome segregation by protecting cohesin at the centromere until sister chromatids separate. MEI-S332 localizes to centromeres as the chromosomes condense in mitosis and meiosis, and it delocalizes as sister chromatids separate. MEI-S332 may control sister-chromatid cohesion in part by affecting the localization or activity of the PP2A-B' phosphatase. The relationship between MEI-S332 and the PP2A-B' phosphatase to which it binds will be investigated, and the function of PP2A-B' in mitosis and meiosis deciphered. Genes involved in MEI-S332 centromere localization will be identified by new genomic RNAi screening methodologies. The meiotic function of condensin and the CPC will be determined and the interactions between these complexes decoded by genetic and cytological experiments. These studies as well as an analysis of the effect of chromatin structure on these complexes will exploit new mutations in condensin, the CPC, and a histone kinase that controls histone modifications critical for meiosis.
The intellectual merit of this project is that it will define the regulation of the critical protein MEI-S332 in chromosome segregation, identify new proteins essential for segregation, and determine the interrelationship between essential protein complexes and the underlying chromatin. The broader impact is that the new proteins recovered are likely to be conserved, thus providing crucial insights into chromosome segregation in humans and plants that will have important implications for human health and agriculture. This laboratory has a record for training and mentoring women to enter scientific research, a commitment that will continue with this project.
