Epithelial organisation and integrity are crucial for the compartmentalisation of an organism and its organs and the regulation of information and energy flow. During early tissue morphogenesis, epithelial cells undergo a transition from a very dynamic and highly proliferative mesenchymal-like state to an immotile quiescent epithelial state. During this process cellular polarity changes from rear-front to apical-basal; a process essential for epithelial function. We are interested in the origin of cell cycle correlations during this process and in the mechanism leading to their desynchronisation. We therefore quantify cell cycle correlations on the tissue level over several generations both in vitro and in silico. Furthermore, we consider their impact on cell migration during tissue morphogenesis. We use Madin-Darby Canine Kidney (MDCK-2) cells as an in vitro model for epithelial tissue morphogenesis and study cell cycle dynamics and cell migration by fluorescence time-lapse microscopy, automated image analysis, and single cell tracking. We determine the narrow distribution of cell cycle periods at low cell density as the cause of the cell cycle correlations. A progressive desynchronisation occurs with each generation of cell divisions. At higher cell density, the desynchronisation process is further accelerated by contact inhibition of proliferation (CIP), resulting in a broadening of the cell cycle period distribution. We suggest that this growth control mechanism ensures the establishment and homeostasis of the emergent epithelial monolayer. Furthermore, we describe a mathematical model for free proliferation at low cell density. Our model confirms the origin of the cell cycle correlations and their progressive desynchronisation and predicts a stationary cell age distribution in case of unlimited growth. Finally, we quantify patterns of cell migration. We observe collective rotations of cell colonies at low cell density and find that changes in this behaviour correlate with mitoses. On the tissue level, synchronous cell divisions therefore involve perturbations of collective migration. Taken together, we conclude that cell cycle correlations in epithelial tissue development are a transient phenomenon and that cells progressively desynchronise by two independent mechanisms, one of stochastic nature, the other one due to contact inhibition of proliferation. In vitro, synchronous cell divisions during early tissue morphogenesis are capable of disturbing tissue morphodynamics, in particular the patterns of collective migration.
|Supervisor:||Hufnagel, Dr. Lars|
|Date of thesis defense:||12 August 2013|
|Date Deposited:||07 Nov 2013 13:56|
|Faculties / Institutes:||The Faculty of Bio Sciences > Dean's Office of the Faculty of Bio Sciences|
|Subjects:||570 Life sciences|
|Uncontrolled Keywords:||cell cyle correlations, epithelial tissue morphogenesis, single cell tracking, image analysis|