CYTODEV · Functions of the midbody ring in embryogenesis and tumorigenesis

Functions of the midbody ring in embryogenesis and tumorigenesis

Project objectives: The main goal of project 326632 CYTODEV was to uncover developmental functions of the cytokinetic midbody and its remnant, a cellular organelle that forms during cell division and who’s functions outside cell division is poorly understood. One key aspect in terms of technology transfer was the implementation of 3D cell and object tracking as well as lineaging at the host institution. Project work performed and results: Overall, CYTODEV was successful concerning the implementation of automated tracking as well as towards elucidating developmental functions of the midbody. Most notably, in the course of the project, we have - uncovered a stereotyped inheritance pattern for midbody remnants in C. elegans - identified a function for the midbody remnant in early axial patterning - implemented algorithms for automated segmentation of cell membranes and midbodies - established national and international collaborations - published our results in the leading journal for developmental biology (Singh D & Pohl C, Dev Cell 28:253-67, 2014) In the course of the project, we have performed tracking of midbodies during wild type development and found that midbody remnant inheritance follows a gradient of cortical contractility from anterior (high) to posterior (low). However, instead of analyzing midbody remnant inheritance in different fate mutants, we have decided to analyze the mechanism of stereotyped midbody remnant inheritance in the early embryo. We uncovered that rotational cortical flow orthogonal to the anteroposterior axis during the division of the AB blastomere in the two-cell embryo positions the cytokinetic midbody remnant of the previous division asymmetrically at the future ventral side of the embryo. In the neighboring P1 blastomere, astral microtubules contact a transient PAR-2-dependent actin coat that forms asymmetrically onto the midbody remnant-P1 interface. Ablation of the midbody remnant or perturbation of rotational cortical flow reveals that microtubule-midbody remnant contacts are crucial for P1 spindle rotation and dorsoventral axis formation. Thus, our findings suggest a mechanism for dorsoventral patterning that relies on coupling of anteroposterior polarity, rotational cortical flow, midbody remnant positioning, and spindle orientation. We have been invited to review our findings (Singh D &Pohl C, Commun Integr Biol 7:e28533, 2014) and presented them at an international conference. Moreover, we have started to analyze a broad range of mutants where this process is altered and have identified a mechanisms that ensures correct midbody remnant placement despite random rotational flow directionality. Additionally, we have started a collaboration with the University of Tennessee, Knoxville, U.S.A. In the course of this collaboration, we will further investigate the use of membrane and midbody segmentation to identify roles of the midbody during apical polarization that occurs during organogenesis. Expected final results and impact: The project could demonstrate that midbody remnants are not just passive structures but participate in polarization events during development. We will continue on identifying additional functions of midbody remnants since it has become clear that they fulfill similar functions in higher vertebrates. Thus, the immediate impact of our study is to provide new mechanistic insights into the role of this neglected organelle with implications for human development and disease. Since our research project was very successful, we have decided to focus on pushing investigations in the direction of investigating the regulation of the new type of cortical contractile flow that we identified. We find that this flow is induced and is part of a mechanical stress response during cell division. We will soon present a study that describes this in detail and also demonstrates its relevance for mammalian cells. Outreach activities I have organized several outreach activities, including a public lecture, a lecture and lab experience for junior high school kids; I supervised several high-school students during lab internships and presented my research at a public state fair. Moreover, we presented our project at several occasions where the public was invited to visit our research institution. All these events allowed us to highlight how basic research on non-vertebrate model organisms can advance several fields of biomedical research. Results of this project can be found at http://www.bmls.de/Developmental_Cell_Biology/aboutus.html.

Data: CORDIS, © European Union