Nucleoli, sites of ribosome biogenesis and the largest structures in the human nucleus, form around nucleolar organiser regions (NORs) located on the short or p-arms of five different chromosomes referred to as acrocentric chromosomes (see McStay 2016). NORs comprise ribosomal genes (rDNA) arrays coding for the major RNA components of ribosomes. How multiple acrocentric p-arms gather together to form a nucleolus and how NORs partition within nucleoli are important but unanswered questions. Progress has been hampered by the inability to distinguish acrocentric p-arms from each other due to their shared DNA-sequences (Van Sluis et al 2019 and Floutsakou et al 2013), see also blog from the Genome Reference Consortium.
To circumvent this impasse, the McStay lab has developed powerful chromosome-engineering approaches on single human chromosomes held in mono-chromosomal somatic cell hybrids. These engineered chromosomes can then be reintroduced into human cells to test function in nucleolar formation (see Mangan and McStay 2021). Using this transformative technology and recently renewed funding from the SFI-HRB-Wellcome Research Partnership, we are currently addressing the following aims.
- Characterise chromosomal requirements for formation of large multivalent nucleoli.
- Identify factor(s) constraining NOR-territories (see Mangan and McStay 2021).
- Explore cellular responses to rDNA DSBs using genome-edited human NORs (see Van Sluis and McStay 2015).
- Construct a minimal NOR-bearing human chromosome by top-down chromosome-engineering.
Additionally we aim to explore tantalising links between rDNA genome-stability and cell-ageing. This work has added significance as nucleoli represent an important paradigm for understanding human genome organisation. This work is supported by an Investigator Award (223049/Z/21/Z) from the SFI-HRB-Wellcome Trust Biomedical Research Partnership.