The cell cycle is the self-reproduction process of the cell, which primarily consists of the duplication and the segregation of genomic DNA. While being the universal minimal unit of growth and heredity, in multicellular organisms, the cell cycle must be coordinated with other developmental processes to generate functional tissues and organs. A collapse of such coordination may lead to tissue degeneration and tumour development. Our lab uses advanced genetics of the multicellular model organism Drosophila melanogaster (fruit fly) to decipher molecular mechanisms that integrate the cell cycle to developmental and homeostatic processes in multicellular organisms. We will further extend our findings into humans by investigating the function of the analogous mechanisms in human cell and tissue culture.
As key effectors that orchestrate the coordination, we mainly focus on a set of evolutionarily conserved proteins commonly referred to as ‘cell cycle regulators’. In particular, we have been studying the function of the anaphase-promoting complex/cyclosome (APC/C), a multisubunit ubiquitin ligase that is 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 to G1/G0 phase.
The current ongoing projects in our lab include the following:
1. Cell-Cycle Regulation of Developmental Signal Transduction and 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 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 Role of Coupling of Centrosome Cycle to Cell Cycle in Cell 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. Regulation of G1/G0 Length in Cellular Quiescence and Genome Stability
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.
- Gambarotto D, Pennetrier C, Rynaiawec JM, et al. Plk4 regulates centriole asymmetry and spindle orientation in neural stem cells. Developmental Cell. in press.
- Kimata Y. APC/C Ubiquitin Ligase: Coupling Cellular Differentiation to G1/G0 Phase in Multicellular Systems. Trends in Cell Biology. in press. online publication Apr. 2019
- 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.
- 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.