Dividing in a tissue
Much of the work on cytokinesis has been done in either replicating singled celled organisms or the first embryonic development of multicellular organisms. From this we have learned a great deal about the mechanisms of ring constriction but cells in our body and other mulicellular organisms don't divide in isolation. Cells in tissues are connected to one another via cell-cell junctions, cell-cell junctions will be covered in the next section, but still divide rapidly. For example, the cells lining your small intestine are dividing so rapidly that the epithelial lining is turning over every 2-4 days! Cells in a tissue have all of the same cell autonomous obstacles to overcome when it comes to cytokinesis but they have many more additional problems and questions to be to solved with the added complexity of being in a tissue. Do dividing cells in a tissue communicate with their neighbors? Do neighboring cells actively participate in cell division? How does the dividing cell overcome the resistive force of neighboring cells? Do cells in a tissue need to produce more force to successfully divide or do neighboring cells become more compliant? Is and or how is the barrier of an epithelium maintained during cell division? Early studies using electron microscopy and immunostaining showed that epithelial cells remain in contact with one another during cell division \cite{Jinguji_1992,Baker1993}. This means that both the dividing cell and the neighboring cell are undergoing large shape changes during cell division. How are both cells responding to these mechanical inputs? Three very exciting papers showed that dividing cells in Drosophila tissue actually break their cell-cell junctions to invaginate the membrane \cite{Guillot2013,Founounou2013,Herszterg2013}. One of the papers even found that there was a loss of adhesion between the dividing cell and the neighboring cell \cite{Guillot2013}. This raises several interesting questions, are the forces from cytokinesis disrupting cell adhesion or is cell adhesion being regulated by non force dependent mechanism? Additionally, why is junction disengagement only happening in certain tissues \cite{Guillot2013}, but not others \cite{Jinguji1992,Baker1993,Founounou2013,Herszterg2013}? Is the barrier function of epithelial tissues being disrupted by forces from cytokinesis and what impacts does this have on the organism? Chapter two of my thesis address whether or not the epithelial barrier is maintained during cytokinesis and how cell-cell junctions respond to the mechanical cues from cytokinesis.