How to cells in new embryos position themselves for further growth?
During its first several cell divisions, a new embryo must set its right from its left, and head from toe. Many studies and genetic analyses have focused on the role of morphogens in triggering cell migration and differentiation. Little attention has focused on the role of simple mechanical forces.
Quantitative, real-time measurement of developing organisms has been limited by the speed of available three-dimensional fluorescence microscopy methods. Moreover, existing approaches required light that would be phototoxic to sensitive organisms with repeated or prolonged exposure.
Mechanical Cues in the Early Embryogenesis of Caenorhabditis elegans
Rolf Fickentscher, Philipp Struntz, and Matthias Weiss
Biophysical Journal. 2013 Oct 105: 1805–1811. PMCID: PMC3797578.
Fickentscher, et al,1 took advantage of advances in imaging techniques over the last decade, using what’s called light-sheet or selective plane illumination microscopy (SPIM) to illuminate only a slice some 700 micrometers in thickness. The gentler light enabled repeated exposure without phototoxicity to growing organisms. A Hamamatsu ORCA-Flash4.0 sCMOS camera, oriented perpendicular to the plane of illumination, captured fluorescence signal from C. elegans embryos expressing GFP-tagged H2B histones and beta-tubulin. The bright signal from the nucleus and cytoskeleton enabled precise tracking of nuclei, cell division and spindle axes.
The high spatial and temporal resolution images showed that the trajectory of each cell during early embryogenesis is highly consistent among embryos. Using a simple mathematical model, the were able to predict cell arrangements up to the 12-cell stage based exclusively on mechanical forces between cells, and between cells and the embryo’s egg shell. The model reliably predicted the cells’ planar positioning and formation of the dorsal-ventral body axis.
Fickentscher, et al,1 relied on the sensitivity and fast frame rates of Hamamatsu’s ORCA-Flash4.0 sCMOS camera to track cell movement without overexposing sensitive developing embryos, using fluorescence microscopy. To explore options for luminescence studies, read how Takeaki Ozawa and colleagues use the ImagEM to detect GPCR binding in Illuminating Activity—in vitro and in vivo.