Assessing photoperturbation using THG imaging of cellularization dynamics in <i>Drosophila</i> embryos.

<p>Principle of cellular front invagination (CFI) speed measurement: (A), transmitted light imaging (wild-type embryo); (B), two-photon imaging (GFP-moesin-tagged embryo, outlining the cell boundaries); (C) and movie 1, THG imaging (wild-type embryo). The images in (A) – (C) are a zoom over the dorsal equatorial region of different embryos, corresponding approximately to the blue square in (D) on a THG image. Images (A) to (C) share the same scale bars. Top, phase 3 of cellularization; middle, phase 4 of cellularization; bottom, kymographs (YT projections) obtained from the time-lapse XY images, showing the propagation of the CFI over time. The dotted black time indicates the limit between phase 3 and phase 4, and the position of the CFI is indicated by a red (resp. green) line in phase 3 (resp. 4). Kymographs shown here as an example were obtained from time-lapse acquisitions with (A) 2 images/min; (B), 1 image/min; (C), 3 images/min. (E), CFI speed calibration as a function of temperature using transmitted light imaging. Errors bars are the standard deviations from 3 different embryos per temperature point.