The role of non-histone proteins in chromosome structure and function during mitosis
The research from our laboratory focuses on three main aims.
1. Making the mitotic chromosome: How do mitotic chromosomes condense, and what is the role of histones and non-histone proteins in shaping them? 2. Segregating the chromosomes: How are centromere specification and kinetochore assembly controlled epigenetically? 3. Controlling the process: How does the chromosomal passenger complex (CPC) regulate chromosome segregation?
Our studies of mitotic chromosome structure this year have focused in three areas: the structure of mitotic chromosomes determined by 3d correlative light and electron microscopy (CLEM) using serial block face scanning EM, the role of condensin in mitotic chromosome architecture and segregation, and the role of histone modifications in driving chromatin compaction in mitosis. The 3D CLEM study led to the surprising conclusion that at least 30% of the mass of mitotic chromosomes is found in a very poorly studied compartment at the chromosome periphery. Studies of condensin function using rapidly degraded alleles and near perfect synchrony of mitotic entry, coupled with CLEM have shown that condensin is required for mitotic chromosome architecture and segregation, but not for compaction of the chromatin in mitosis. Instead, studies assembling chromatin from highly purified histones suggest that the spectrum of posttranslational modifications on the histones may be a key factor driving mitotic chromatin compaction.
Our studies of chromosome segregation have focused largely on the use of human synthetic artificial chromosomes to probe the role of epigenetics and mitotic transcription in centromere stability and function. We showed that removing the modification H3K4me2 from centromeres causes a loss of centomeric transcription and inactivation of the centromere. Induction of H3K9ac, a mark formed in response to transcription, is able to compensate for this loss of H3K4me2. These experiments led to a hypothesis that centromeric transcription and resulting H3K9ac provide a defence against invasion of the centromere by surrounding heterochromatin. We also moved beyond our studies of the synthetic artificial chromosome, publishing our first work using PREditOR (protein reading and editing of residues), a synthetic biology approach to using diverse mark:reader pairs to manipulate diverse cellular signalling pathways. This year, a pilot study showed that we can rapidly and efficiently remove all heterochromatin from cells using synthetic protein tools.
Our studies of mitotic regulation have led us to examine the effects of altering the dynamics of chromosome passenger complex association with centromeres. Interestingly, dampening CPC dynamics at centomeres causes a mitotic delay in response to activation of the spindle assembly checkpoint.
Our work is supported by a Wellcome Trust Principal Research Fellowship to Bill Earnshaw.
Wood, L, D.G. Booth, G. Vargiu, S. Ohta, F. deLima Alves1,5, K. Samejima, T. Fukagawa, J. Rappsilber and W.C. Earnshaw. (2016). Auxin/AID versus conventional knockouts: distinguishing the roles of CENP-T/W in mitotic kinetochore assembly and stability. OPEN BIOLOGY 6: 150230. PMID: 26791246; DOI: 10.1098/rsob.150230.
Molina O., G. Vargiu, M.A. Abad1, A. Zhiteneva, J. Arulanandam, H. Masumoto, N. Kouprina, V. Larionov and William C Earnshaw. (2016) Epigenetic engineering reveals a balance between histone modifications and transcription in kinetochore maintenance. NATURE COMMUN. 7:13334. PMID: 27841270; DOI: 10.1038/ncomms13334.
Booth D.G., A.J. Beckett, O. Molina, I. Samejima, H. Masumoto, N. Kouprina, V. Larionov, I.A. Prior and W.C. Earnshaw. (2016). 3D-CLEM reveals that a major portion of mitotic chromosomes is not chromatin MOL. CELL. 64:790-802. PMID: 27231315; DOI: 10.1016/j.molcel.2016.10.009