Structural biology of cell division
Known among his colleagues and peers as JP, Jeyaprakash is a Wellcome Senior Research Fellow at the Wellcome Centre for Cell Biology, University of Edinburgh, UK. He completed his PhD on the understanding of molecular determinants of carbohydrate specificities of plant lectins in 2004 at the Indian Institute of Science, Bangalore with Prof. M. Vijayan. After his PhD, JP obtained Alexander von Humboldt and Marie-Curie Fellowships to work with Prof. Elena Conti at EMBL-Heidelberg and subsequently at the Max-Planck Institute of Biochemistry, Martinsried, Germany, where he became interested in understanding the molecular mechanisms of accurate cell division. In 2012, he started his independent research group supported by a Wellcome Career Development fellowship and was awarded a Wellcome Senior Research Fellowship in 2017. He has recently been awarded an ERC advanced grant (2022). JP’s lab is interested in understanding high-resolution mechanistic details of processes regulating centromere inheritance and chromosome segregation. His major contributions thus far include the structural characterisation of the Chromosomal Passenger Complex and the Ska complex, key protein assemblies involved in the physical attachment of chromosomes to spindle microtubules during cell division.
Maria Alba Abad Fernandaz, Thomas Davies, Lorenza Di Pompeo, Anjitha Gireesh, Bethan Medina, Paula Sotelo and Pragya Srivastava
Structural biology of cell division
Accurate distribution of chromosomes to the daughter cells during cell division requires selective stabilisation of chromosome-microtubule attachments, capable of supporting chromosome bi-orientation (where sister chromatids are attached to microtubules emanating from opposite spindle poles) and maintaining sister-chromatid cohesion until all sister-chromatids achieve bipolar attachment. Two chromosomal sites work at the heart of these processes: the centromere, defined by the enrichment of CENP-A (a Histone H3 variant) nucleosomes, and the inner centromere, which lies between the two sister-chromatids. The centromere acts as an assembly site for the kinetochore, where microtubules attach. Unlike canonical chromatin, CENP-A nucleosome undergo DNA replication-mediated dilution due to the distribution of existing CENP-A to the newly made DNA strand during each round of the cell cycle. To preserve centromere identity and hence to maintain the microtubule attachment site at the right place, CENP-A levels must be replenished during each cell cycle round. The inner centromere acts as a signalling/regulatory hub, recruiting factors that regulate kinetochore-microtubule attachments and control timely sister-chromatid separation.
We have a good understanding of the mechanisms controlling the assembly and function of the kinetochore. However, structural and molecular bases for the mechanisms underlying the maintenance of centromere identity and the establishment of the centromere-associated regulatory interaction network are just emerging. The overarching goal of our current work is to obtain high-resolution, mechanistic understanding of centromere/inner centromere assembly and their function in ensuring accurate segregation of chromosomes during cell division. This is crucial as defective chromosome segregation often results in aneuploidy, a chromosomal numerical aberration implicated in miscarriages, infertility, birth defects and several human cancers.
Exploiting our experience in integrating structure-function approaches (X-ray crystallography, cryo electron microscopy, Crosslinking/Mass Spectrometry, biochemical/biophysical methods with human cell-line based functional assays) to study chromosome segregation, we currently aim to address three important questions:
1. How is the inner centromere signalling/regulatory platform established?
2. How does the inner centromere recruit enzymatic activities to ensure accurate chromosome segregation?
3. How is the centromere identity preserved through generations of cell division?
Recently, we discovered that the Chromosomal Passenger Complex (CPC), which is a major centromere associated regulator of chromosome segregation has an intrinsic nucleosome binding activity essential for its chromosome association and function (Abad et al., 2019, J Cell Biol). We have also characterised the molecular basis for how CPC interacts with Sgo1, a key regulator of sister-chromatid cohesion (Abad et al., 2021, bioRXiv).
Our ongoing and future work will provide unprecedented details of centromere-mediated control of chromosome segregation and allow us to build a comprehensive mechanistic model for error-free chromosome segregation, a process that has been fascinating researchers for more than a century.
A. Overview of proposed pathways responsible for the centromere localization of the Chromosomal Passenger Complex (CPC; Borealin, Survivin, INCENP and Aurora B), a master regulator of chromosome segregation. Two histone phosphorylations, Histone H3 Thr3 (H3T3p) and Histone H2A Thr120 (H2AT20p), mediated by Haspin and Bub1 kinases respectively, recruit CPC to the inner centromere. CPC binds H3T3p directly via Survivin and H2AT120p indirectly via Sgo1.
B. Molecular basis for CPC-Sgo1 interaction: CPC-Sgo1 binding requires physical recognition of Histone H3 like N-terminal tail of Sgo1 by Survivin. Disrupting this interaction perturbs CPC centromere association and leads to chromosome missegregation.
Abad, M. A*., Gupta, T*., Hadders, M, A., Meppelink, A., Wopken, J. P., Blackburn, E., Zou, J., Buzuk, L., Kelly, D, A., McHugh, T., Rappsilber, J., Lens, S. M. A and Jeyaprakash, A. A. (2021) Molecular Basis for CPC-Sgo1 Interaction: Implications for Centromere Localisation and Function of the CPC. bioRxiv Doi: https://doi.org/10.1101/2021.08.27.457910 (*equal contribution)
Medina-Pritchard, B., Lazou, V., Zou, J., Byron, O., Abad, M. A., Rappsilber, J., Heun, P and Jeyaprakash, A. A. (2020) Structural Basis for Centromere Maintenance by Drosophila CENP-A Chaperone Cal1. EMBO J e103234. Doi:10.15252/embj.2019103234
Abad, M. A., Ruppert, J. G*., Buzuk, L*., Wear, M. A., Zou, J., Webb, K. M., Kelly, D. A., Voigt, P., Rappsilber, J., Earnshaw, W. C and Jeyaprakash, A. A. (2019) Direct Nucleosome Binding of Borealin Secures Chromosome Association and Function of the CPC. J Cell Biol 218, 3912-3925. (*equal contribution)