The “cell cycle” is the self-reproduction process of cells, which primarily consists of the duplication and the segregation of genomic DNA. While being the universal minimal unit of heredity, in multicellular organisms, the cell cycle must coordinate with cellular differentiation and morphogenesis to generate functional tissues and organs. A collapse of such coordination leads to tissue degeneration and tumour development. Our lab uses advanced genetics of the model organism Drosophila melanogaster (fruit fly) and mammalian cells to decipher molecular mechanisms that integrate the cell cycle to developmental and homeostatic processes in multicellular organisms.
As key effectors of such a coordination mechanism, we are interested in the role of a set of evolutionarily conserved proteins commonly referred to as ‘cell cycle regulators’. In particular, we have been focusing on the anaphase-promoting complex/cyclosome (APC/C), a multisubunit ubiquitin ligase known to target numerous proteins for ubiquitin-mediated degradation during the cell cycle. Mounting evidence including our recent studies highlights the pivotal role of the APC/C in coupling cell fate determination and cellular differentiation with G1/G0 cell cycle phase.
Our current interests are focused on, but not limited to, the following specific aspects:
1. The Cell-Cycle Regulation of Developmentally Controlled Transcription
A wide spectrum of cell behaviour, including cell division and differentiation, is essentially dictated by developmentally regulated transcription, which, in turn, is determined by the complex choreography of cell signalling and transcription factors. We have recently found that the APC/C suppresses the transcriptional activity of the conserved extracellular signalling pathway, the Wingless (Wg)/Wnt pathway, upon the G1 arrest prior to retinal differentiation during Drosophila eye development (Martins et al., 2017 Developmental Cell). This inhibition of Wnt signalling is mediated by the degradation of a positive Wnt modulator and a conserved centrosomal kinase, Nek2. This study highlighted a novel role of cell cycle regulators in modulating the activity of developmental signalling to coordinate cell fate determination with cell cycle progression. We are therefore extending this study by pursuing the following projects:
- Elucidating the function of Nek2 in the cell cycle regulation of Wnt signalling and the centrosome during Drosophila development
- Investigating the role of the APC/C-Nek2 axis in Wnt regulation in human cells and mammalian intestinal epithelia
- Investigating the role of the G1/G0 phase on gene expression and patterning
In these projects, we are collaborating with Marc de la Roche (University of Cambridge), Andrew Fry (University of Leicester) and Robert Krauz (Gurdon Institute).
2. The Centrosome-Cell Cycle in Cellular Differentiation and Cell Polarity
The centrosome is a gigantic organelle serving as a major microtubule-organising centre in animal cells and, through the cytoskeletal organisation, provides a cell with directional and positional cues within the tissue. Importantly, dysfunction of the centrosome is associated with various genetic disorders, including microcephalies and ciliopathies, whilst supernumerary centrosomes are known as a hallmark of cancer cells. The APC/C is localised at the centrosome and controls the levels of some critical centrosome components in Drosophila tissues and human cells.
In the collaboration with David Glover’s lab and Pietro Lio’s lab (University of Cambridge), we conducted the proteomic analysis of in vivo APC/C-interacting proteins in developing Drosophila tissues(Haider et al., 2015 BioData Mine). We identified a conserved centrosomal component Spd2 as the centrosomal linker of the APC/C. Spd2 recruits the APC/C activator Fzr/CDH1 onto the centrosome upon mitotic exit to promote the degradation of Aurora A, a conserved centrosomal substrate of the APC/C. This interaction is critical for maintaining the homeostasis of neural stem cells in the developing adult brain (Meghini et al., 2016 Nature Comms). We also showed that Spd2 is also an APC/C substrate, suggesting the presence of a feedback mechanism for the centrosomal activity of the APC/C. Based on these findings, we are currently investigating:
- The role of Spd2 degradation in the asymmetric division of the Drosophila neural stem cell and branching of neurons
- The role of the dissociation of Fzr from the centrosome in stem cell survival
- The role of APC/C-dependent degradation of centrosomal components in the centrosome cycle
In these projects, we are collaborating with Renata Basto (Institute Curie), Sofia Arujo (University of Barcelona) and Hiroyuki Yamano (University College London)
3. The Mechanism of the Prolonged G1, G0, Phase
We are also interested in the role of prolonged G1 arrest, or the “G0” phase, which coincides with terminal differentiation and cellular quiescence. The APC/C co-activator, Fzr/Cdh1, is considered one of the master regulators of the progression of the G0 phase (Cappel et al., 2016 Cell). Using Drosophila genetics and genetic resources, we have been conducting gain-of-function and loss-of-function screens to identify the key cell cycle regulators that cooperate with Fzr/Cdh1 to regulate G0 progression in vivo. We are also generating fluorescent reporters that will enable visualisation of the precise order of molecular events that take place upon the entry and exit from G0.
- Martins T, Meghini F, Florio F, Kimata Y. The APC/C coordinates retinal differentiation with G1 arrest through the Nek2-dependent modulation of Wingless signalling. Developmental Cell. 2017 Jan. online publication Dec 2016.
- Meghini F, Martins T, Tait X (equally contributed), Fujimitsu K, Yamano H, Glover DM, Kimata Y. Targeting of Fzr/Cdh1 for timely activation of the APC/C at the centrosome during mitotic exit. Nature Comms. 2016 Aug 25;7:12607.
- Haider S, Lipinszki Z, Przewloka MR, Ladak Y, D’Avino PP, Kimata Y, Lio’ P, Glover DM. DAPPER: a data-mining resource for protein-protein interactions. BioData Min. 2015 Sep 24;8:30.
- Kimata Y, Kitamura K, Fenner N, Yamano H. Mes1 controls the meiosis I to meiosis II transition by distinctly regulating the anaphase-promoting complex/cyclosome coactivators Fzr1/Mfr1 and Slp1 in fission yeast. Mol Biol Cell. 2011 May; 22(9):1486-9
- Kimata Y, Baxter JE, Fry AM, Yamano H. A role for the Fizzy/Cdc20 family of proteins in activation of the APC/C distinct from substrate recruitment. Mol Cell. 2008 Nov 21; 32(4):576-83
- Kimata Y, Trickey M, Izawa D, Gannon J, Yamamoto M, Yamano H. A mutual inhibition between APC/C and its substrate Mes1 required for meiotic progression in fission yeast. Dev Cell. 2008 Mar; 14(3):446-54
- Hayes MJ, Kimata Y (equally contributed), Wattam SL, Lindon C, Mao G, Yamano H, Fry AM. Early mitotic degradation of Nek2A depends on Cdc20-independent interaction with the APC/C. Nat Cell Biol. 2006 Jun; 8(6):607-14