Cell adhesion, epithelial morphogenesis and cellular reorganisation

 Department of Biological Sciences, TIFR, Mumbai 400005, India

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UNDERSTANDING THE MOLECULAR, CELLULAR AND PHYSICAL BASES OF CELLULAR REORGANISATION

 

IN A NUTSHELL

Cells in multicellular organisms are organised in layers that have “self-organising” properties. Single cells within the layer can exhibit seemingly stochastic behaviours in response to (as yet unidentified) signals. Neighbouring cells in the layer can integrate signals from single cells and coordinate their behaviours to exhibit complex social behaviours so that the integrity of the layer is maintained.  Cells can therefore be thought of as possessing a rudimentary intelligence. The work in our lab seeks to understand the cellular, molecular and physical bases of cellular intelligence that facilitates cellular reorganisation using a combination of model organism genetics (in the fruitfly, Drosophila melanogaster), molecular-, cell- and systems biology and laser induced perturbations. This will enable an understanding of how epithelial homeostasis is maintained in the face of naturally occurring perturbations (cell division, cell delamination, cell death) as well as of mechanisms that operate to heal wounds and prevent misbehaviour such as cancer metastases.

 MORE SPECIFICALLY SPEAKING

The ability of cells to reorganize must rely on their ability to communicate with their neighbours, mediated in large part through the physical contact between cells. This physical contact is mediated by transmembrane molecules (notably adhesion molecules, of which cadherins and integrins are most predominant)  which organize the formation of two molecular networks on either side of ultrastructurally distinct cellular junctions. By so doing, they facilitate the transmission of both chemical signals and physical forces between cells and interfaces. These signals in turn determine what a cell decides to do.

The goal of the research being done in my lab is to understand the cell biological, molecular and physical bases of cellular reorganisation that results from the integration and tight coordination of cell behaviours in space and time. Specifically, we are trying to understand i) how inputs from adhesion molecules and mechanical stimuli (adhesion molecules are the best characterised mechanosensors, Vogel and Sheetz) are integrated by cells to result in specific changes in their shape/morphology and behaviour,  ii) how interactions between molecules influences the strength of adhesion, iii) the nature of the forces/physical constraints that the molecules exert to facilitate specific cell behaviours and iv) to visualize modulations in adhesion strength and the dynamics of molecular interactions  in real time in a living organism in relation to specific cell behaviours.

PERSPECTIVES

Our work lies at the interface between cell and developmental biology where many exciting advances have been facilitated by advances in microscopy (reviewed in Narasimha and Brown 2006) and extends to include biophysical approaches (laser   and mechanical perturbations, laser mediated protein inactivation) through collaborations with colleagues at TIFR (G.V.Shivashankar, NCBS). These multidisciplinary approaches are expected to provide a holistic understanding of the bases of cell behaviour in real-time in a living organism, working at the level of a single cell or a small group of cells in the context of a morphogenetic movement occurring during normal embryonic development (that resembles wound healing) and in a genetically induced perturbation of this behaviour that provides an excellent in vivo model for metastatic cell behaviour in cancers in a whole living organism.

MODEL SYSTEMS

Dorsal closure: normal , perturbed (Drosophila embryogenesis)

Development of an epithelial bilayer (Drososphila pupal wing)

Forming axon bundles (Drosophila Embryonic nervous system)

Formation of cell clusters (Drosophila eye)

Adhesion and layer formation (mouse ES cells)

 

TOOLS OF THE TRADE

Genetics (Drososphila) including targeted RNA interference screens

Molecular biology, Biochemistry

Microarray and Proteome analysis

Cell biology including 3D and 4D-real time confocal microscopy, FRAP, FRET

Mechanical and laser induced perturbations

Cell culture including establishment of  primary Drosophila tissue cultures, established Drosophila cell lines and mouse ES Cells

 

USEFUL READING:

1) Jacinto A, Woolner S, Martin P. 2002. Dynamic analysis of dorsal closure in Drosophila: from genetics to cell biology. Dev Cell. 3(1):9 -19.

2) Narasimha M, Brown NH. 2006. Confocal microscopy of Drosophila embryos. In “Cell biology: a laboratory manual”, Julio De Celis, Editor, Academic Press.

3) Narasimha M, Brown NH. 2004. Novel functions for integrins in epithelial morphogenesis. Curr Biol.14(5):381-5.

4) Narasimha, M and Brown, NH (2006). Integrins and associated proteins in Drosophila development. In ‘Integrins and development’. Landes Bioscience (Erik Danen, Editor) Published online @ http://www.eurekah.com/abstract.php?chapid=2406&bookid=181&catid=20.

5)Torgler, C., Narasimha, M., Knox, A.L., Vernon, M., Zervas, C and Brown, N.H. 2004.

Drosophila tensin stabilizes integrin contacts in Drosophila. Developmental Cell, 6, 357 -36

 

 

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