Role of CIZ1 in X chromosome inactivation

CIZ1 is a nuclear matrix protein that plays a role in DNA replication by delivering cyclin-dependent protein kinases to their site of action on the nuclear matrix during late G1 phase. We recently showed that CIZ1 is recruited to the inactive X chromosome early in development, where it plays a role in recruitment of Xist RNA and the epigenetic silencing process. CIZ1-dependent acquisition of repressive chromatin marks is cell-cycle dependent raising questions about the mechanism of silencing and its relationship with the DNA replication function of CIZ1.

The project is timely because the link between CIZ1 and X-inactivation is not yet in the public domain and we have a significant head start, and novel because, to our knowledge, no competing group is currently working on this. We do now have collaborators in Oxford (Prof. Neil Brockdorff who is a world leader in this field), which presents significant opportunity to a student when thinking about their next steps. We also have a unique working hypothesis and some preliminary data (and working assays), which suggests that the role of CIZ1 is to move template from A to B inside the nucleus (Eg replication origins into replication factories, Xi into perinucleolar PRC domains). This raises many new questions about mechanism, which could involve intranuclear microtubules or LNCRNAs (both are novel).

This project will harness a rich archive of molecular tools (antibodies, genetically altered cell lines, constructs) to investigate this relationship, using cultured mammalian cells, synchronisation procedures, nuclear fractionation and quantitative immune-detection techniques. It is likely that the project will also use molecular biology techniques to generate a series of constructs that dissect Xist and NM-interaction domains in CIZ1.