Fig. 2: The dynamics of the Brillouin shift at the cellular level.
From: Highly dynamic mechanical transitions in embryonic cell populations during Drosophila gastrulation
a Cell-by-cell profile of the BS (in GHz, left column) along 16 cells of the mesoderm (8 cells on each side of ventral midline, center columns) from the onset of gastrulation to ventral fold initiation. Cell position is shown along x-axis and within the first timepoint of the CaaX-eGFP column. White-dashed line indicates the quantified 16-cell area. Left column: line is the mean BS shift within each cell, grey area is standard error of the mean (SEM). Three slices in each of four embryos were quantified (N = 4). b Subcellular localisation of largest 4% of the BS dynamic range during VFF (enclosed with white-dashed line in right column; overlayed in left and center columns. Cell membranes: CaaX-eGFP, in magenta; nuclei: H2Av-mRFP, in cyan. White dashed line in CaaX-eGFP and H2Av-mRFP columns connects the apical side of nuclei across central mesodermal cells. c The progression of squamous morphogenesis in dorsal cells: from columnar (left/center-left; blue/white outlines), through a short columnar/cuboidal intermediate (center-right; blue/white outlines) to a squamous shape (right; blue/white outlines). Phase 1 and phase 2 were distinguished by the cuboidal intermediate timepoint (see Methods). Top panel: membranes labelled with CaaX-eGFP, bottom panel: BS map (in GHz). Asteriks (*) indicate excluded cells from analyses for being considered amnioserosa cells (6 cells). Scale bar is 25 μm. d Box-whiskers plot showing major/minor axes length ratio (N = 9) of columnar, cuboidal (max. circularity, see Methods) and squamous/elongated shapes. e Box-whiskers plot showing fold changes in apical-basal and stretching axes length from the end of cellularisation until cells reach maximum circularity value (phase 1), and from that timepoint until they become squamous (phase 2). Each dot is a quantified cell (N = 9). f Time course of the cell-by-cell means of the BS (yellow: normalisation to time = 0’: end of cellularisation), and the apical-basal (a, b, cyan) and stretching (magenta) axes lengths (in μm) during squamous morphogenesis. N = 7, (see Methods). Error bars: standard error of the mean (SEM). Box-whiskers plots: line is median, top/bottom edges are 1st and 3rd quartiles and whiskers indicate maximum and minimum values. Source data are provided as a Source Data file. BS is Brillouin shift. For statistical comparisons * is p < 0.05, ** is p < 0.01.
