Video force microscopy reveals the mechanics of ventral furrow invagination in Drosophila
- aDepartment of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON, Canada N2L 3G1;
- bDepartment of Biology, University of Waterloo, Waterloo, ON, Canada N2L 3G1;
- cPhysics Department, King’s College London, London WC2R 2LS, United Kingdom;
- dDepartment of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235;
- eInstituto de Medicina Molecular, 1649-028 Lisbon, Portugal;
- fSkirball Institute of Biomolecular Medicine, New York Hospital, New York, NY 10016; and
- gMRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, United Kingdom
See allHide authors and affiliations
Edited by William A. Eaton, National Institutes of Health-National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, and approved October 20, 2010 (received for review May 13, 2010)

Abstract
The absence of tools for mapping the forces that drive morphogenetic movements in embryos has impeded our understanding of animal development. Here we describe a unique approach, video force microscopy (VFM), that allows detailed, dynamic force maps to be produced from time-lapse images. The forces at work in an embryo are considered to be decomposed into active and passive elements, where active forces originate from contributions (e.g., actomyosin contraction) that do mechanical work to the system and passive ones (e.g., viscous cytoplasm) that dissipate energy. In the present analysis, the effects of all passive components are considered to be subsumed by an effective cytoplasmic viscosity, and the driving forces are resolved into equivalent forces along the edges of the polygonal boundaries into which the region of interest is divided. Advanced mathematical inverse methods are used to determine these driving forces. When applied to multiphoton sections of wild-type and mutant Drosophila melanogaster embryos, VFM is able to calculate the equivalent driving forces acting along individual cell edges and to do so with subminute temporal resolution. In the wild type, forces along the apical surface of the presumptive mesoderm are found to be large and to vary parabolically with time and angular position, whereas forces along the basal surface of the ectoderm, for example, are found to be smaller and nearly uniform with position. VFM shows that in mutants with reduced junction integrity and myosin II activity, the driving forces are reduced, thus accounting for ventral furrow failure.
Footnotes
- 1To whom correspondence should be addressed. E-mail: brodland{at}uwaterloo.ca.
Author contributions: G.W.B., M.S.H., and A.J. designed research; G.W.B., V.C., P.G.C., J.V., F.U., and B.B. performed research; G.W.B., V.C., P.G.C., J.V., S.N., and F.U. contributed new reagents/analytic tools; G.W.B., V.C., J.V., B.B., and M.M. analyzed data; and G.W.B., V.C., M.S.H., B.B., and M.M. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1006591107/-/DCSupplemental.
Freely available online through the PNAS open access option.
Citation Manager Formats
Article Classifications
- Biological Sciences
- Biophysics and Computational Biology